Frequently Asked Questions - Part 1 of 3

Frequently Asked Questions (part 1/3)
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Archive-name: compression-faq/part1
Last-modified: Sep 5th, 1999

It is insufficiently considered that
men more often require to be reminded
than informed.
Samuel Johnson


This file is part 1 of a set of Frequently Asked Questions (FAQ) for
the groups comp.compression and comp.compression.research. If you
can't find part 2 or 3, see item 53 below. A copy of this FAQ is available
by ftp in ftp://rtfm.mit.edu/pub/usenet/news.answers/compression-faq/
files part1 to part3. This FAQ is also accessible in the World Wide Web at
http://www.faqs.org/faqs/compression-faq/part1/preamble.html or
http://www.cis.ohio-state.edu/hypertext/faq/usenet/compression-faq/top.html

Certain questions get asked time and again, and this is an attempt to
reduce the bandwidth taken up by these posts and their associated
replies. If you have a question, *please* check this file before you
post. It may save a lot of peoples time.

If you have not already read the overall Usenet introductory material
posted to "news.announce.newusers", please do. It is also available by
ftp in ftp://garbo.uwasa.fi/pc/doc-net/ (see item 2 below
about .zip).

If you don't want to see this FAQ regularly, please add the subject
line to your kill file. If you don't know what a kill file is, get by
ftp the file ftp://rtfm.mit.edu/pub/usenet/news.answers/
If you have corrections or suggestions for this FAQ, send them to
Jean-loup Gailly <jloup at gzip.org>. (Replace " at " with " (AT) ". This is
a protection against junk mail. Sorry for the inconvenience.)

Part 1 is oriented towards practical usage of compression programs.
Part 2 is more intended for people who want to know how compression works.
Part 3 is a long (but somewhat obsolete) list of image compression hardware.

Main changes relative to the previous version:

- LZO page moved [item 2]
- new url for the File Format Collection [items 2 & 54]
- new url for ACE [item 2]
- new pkzip version [item 3]
- fixed url for arithmetic coder [item 13]
- add url for DjVu, an image compression library [item 15]
- remove obsolete link [item 15]
- new url for DCT algorithms [item 15]
- add url for lossless image compression benchmarks [item 16]
- added urls for the MP3 audio compression standard, and for benchmarks
of lossless audio compression programs [item 26]

Contents
========

General questions:

[1] What are these newsgroups about?
[2] What is this .xxx file type?
Where can I find the corresponding compression program?
[3] What is the latest pkzip version?
[4] What is an archiver?
[5] What is the best general purpose compression program?
[7] Which books should I read?
[8] What about patents on data compression algorithms?
[9] Compression of random data (WEB, Gilbert and others)
[10] Fake compression programs (OWS, WIC)
[11] What is the V.42bis standard?
[12] I need source for the winners of the Dr Dobbs compression contest
[13] I need source for arithmetic coding

Image and audio compression:

[15] Where can I get image compression programs?
[16] What is the state of the art in lossless image compression?
[17] What is the state of fractal compression?
[18] I need specs and source for TIFF and CCITT group 4 Fax.
[19] What is JPEG?
[20] I am looking for source of an H.261/H.263 codec and MPEG
[25] Fast DCT (Discrete Cosine Transform) algorithms
[26] Are there algorithms and standards for audio compression?

Common problems:

[30] My archive is corrupted!
[31] pkunzip reports a CRC error!
[32] VMS zip is not compatible with pkzip!
[33] I have a problem with Stacker or DoubleSpace!

Questions which do not really belong to comp.compression:

[50] What is this 'tar' compression program?
[51] I need a CRC algorithm
[52] What about those people who continue to ask frequently asked questions?
[53] Where are FAQ lists archived?
[54] I need specs for graphics formats
[55] Where can I find Lenna and other images?
[56] I am looking for a message digest algorithm
[57] I have lost my password on a .zip file


Part 2: (Long) introductions to data compression techniques

[70] Introduction to data compression (long)
Huffman and Related Compression Techniques
Arithmetic Coding
Substitutional Compressors
The LZ78 family of compressors
The LZ77 family of compressors

[71] Introduction to MPEG (long)
What is MPEG?
Does it have anything to do with JPEG?
Then what's JBIG and MHEG?
What has MPEG accomplished?
So how does MPEG I work?
What about the audio compression?
So how much does it compress?
What's phase II?
When will all this be finished?
How do I join MPEG?
How do I get the documents, like the MPEG I draft?

[72] What is wavelet theory?
[73] What is the theoretical compression limit?
[74] Introduction to JBIG
[75] Introduction to JPEG
[76] What is Vector Quantization?
[77] Introduction to Fractal compression
[78] The Burrows-Wheeler block sorting algorithm


Part 3: (Long) list of image compression hardware

[85] Image compression hardware
[99] Acknowledgments


Search for "Subject: [#]" to get to question number # quickly. Some news
readers can also take advantage of the message digest format used here.

If you know very little about data compression, read question 70 in
part 2 first.

--------------------------------------------------------------------------------

Subject: [1] What are these newsgroups about?


comp.compression is the place to discuss about data compression, both
lossless (for text or data) and lossy (for images, sound, etc..).
comp.compression.research was created later to provide a forum for
current research on data compression and data compression algorithms;
this group is now moderated. If you are not experienced in data compression,
please post in comp.compression only.

An archive of this newsgroup since Oct 1993 is available in
ftp://spib.rice.edu/spib/news/comp.compression/

Excellent collections of compression based information are provided at
http://www.internz.com/compression-pointers.html and
http://www.sr3.t.u-tokyo.ac.jp/~arimura/compression_links.html

If you only want to find a particular compression program for a
particular operating system, please read first this FAQ and the
article "How to find sources" which is regularly posted in
news.answers.

If you can't resist posting such a request, other groups are probably
more appropriate (comp.binaries.ibm.pc.wanted, comp.os.msdos.apps,
comp.sources.wanted, comp.sys.mac.wanted, comp.archives.msdos.d, comp.dsp,
alt.graphics.pixutils). Please post your request in comp.compression
only as a last resource.

If your question is about graphics only (no compression), please
post to comp.graphics.misc, *after* reading the comp.graphics FAQ (see
item 54 below). For some unknown reason, many questions about
graphics are incorrectly posted to comp.compression.
For questions related to audio compression, check also comp.dsp.

Please do not post any program in binary form to comp.compression.
Very short sources can be posted, but long sources should be be posted
to the specialized source groups, such as comp.sources.* or alt.sources.
If the program is already available by ftp, just give the name of the
ftp site and the full path name of the file.

As for any newsgroups, do not post the same message separately to
comp.compression and comp.compression.research.

--------------------------------------------------------------------------------

Subject: [2] What is this .xxx file type?
Where can I find the corresponding compression program?


All the programs mentioned in this section are lossless. For most
programs, one US and one European ftp site are given. (ftp.simtel.net
and garbo.uwasa.fi) Many other sites (in particular wuarchive.wustl.edu)
have the same programs.

To keep this list to a reasonable size, many programs are not mentioned
here. When several programs can handle the same archive format, only one of
them is given. If you don't find a particular archiver here, look also in:
ftp://ftp.cs.tu-berlin.de/pub/msdos/mirrors/ftp.elf.stuba.sk/pc/
ftp://garbo.uwasa.fi/pc/arcers/
ftp://ftp.fh-koblenz.de/pub/Packers/

Sources for additional lossless data compressors can be found in
ftp://garbo.uwasa.fi/pc/programming/lds_11.zip
ftp://ftp.simtel.net/pub/simtelnet/msdos/arcutils/lz-comp2.zip
http://wwwvms.utexas.edu/~cbloom/index.html
ftp://ftp.imag.fr/pub/archive/compression/codecs/
ftp://garbo.uwasa.fi/pc/turbopas/ (sources in Pascal)
ftp://ftp.cs.uiowa.edu/pub/jones/compress/ (Splay tree compression)

For Macintosh programs, look on ftp://wuarchive.wustl.edu/systems/mac/info-mac/
or in http://hyperarchive.lcs.mit.edu/HyperArchive.html
For VM/CMS, look on ftp://vmd.cso.uiuc.edu/
For Atari, look on ftp://atari.archive.umich.edu
For Amiga, look on ftp://ftp.wustl.edu/pub/aminet/util/

A general purpose lossless data compression library is available in
ftp://ftp.cdrom.com/pub/infozip/zlib/ or zlib113.zip;
see http://infozip.cdrom.com/pub/infozip/zlib/ for more information.
Another library favoring speed over compression ratio is available at
http://wildsau.idv.uni-linz.ac.at/mfx/lzo.html

If you don't know how to use ftp or don't have ftp access, read the
article "How to find sources" which is regularly posted in news.answers.

If you can't find a program given below, a newer version probably exists in
the same directory. Tell me at <jloup at gzip.org>

A very short description of the compression algorithm is given for most
programs. For the meaning of LZ77, LZ78 and LZW, see question 70 in part 2 of
the FAQ. If you are looking for the file format of a specific compression
program, look at "The File Format Collection" in http://www.wotsit.org
and/or get the sources of the decompressor. For the format of uuencode, do
"man 5 uuencode" on a Unix box.

ext: produced by or read by

.ace: ACE
http://members.aol.com/mlemke6413/ace.htm

.arc, .ark: arc, pkarc for MSDOS. (LZW algorithm)
ftp://ftp.simtel.net/pub/simtelnet/msdos/arcers/pk361.exe
ftp://garbo.uwasa.fi/pc/arcers/

arc for Unix
ftp://ftp.ddj.com/packages/arc521e.tar.Z
ftp://garbo.uwasa.fi/unix/arcers/
Contact: Howard Chu <hyc (AT) highlandsun.com>

arc for VMS
ftp://wuarchive.wustl.edu/packages/compression/vax-vms/arc.exe

for Mac
ftp://wuarchive.wustl.edu/systems/mac/info-mac/cmp/

arc for Amiga
ftp://ftp.funet.fi/pub/amiga/fish/001-100/ff070/arc.lha

.arj: arj for MSDOS (LZ77 with hashing, plus secondary static Huffman
encoding on a block basis)
Contact: Robert K Jung <robjung (AT) world.std.com>
http://www.arjsoft.com
ftp://ftp.simtel.net/pub/simtelnet/msdos/arcers/arj250a.exe
ftp://garbo.uwasa.fi/pc/arcers/

unarj for Unix. Decompresses only. (There is no arj compressor for Unix.
Don't post a request.)
ftp://oak.oakland.edu/pub/misc/unix/
ftp://garbo.uwasa.fi/unix/arcers/

unarj for Mac
ftp://mac.archive.umich.edu/mac/util/compression/

unarj for Amiga
ftp://ftp.funet.fi/pub/amiga/utilities/archivers/

base64 (MIME encoding): This is *not* a compression issue but it keeps
coming as a question on comp.compression. So:
ftp://ftp.andrew.cmu.edu/pub/mpack/mpack-1.5-src.tar.Z (source)
ftp://ftp.andrew.cmu.edu/pub/mpack/mpack15d.zip (MSDOS exe)
ftp://wuarchive.wustl.edu/systems/mac/info-mac/cmp/ (Mac)
ftp://garbo.uwasa.fi/pc/decode/

.bck: VMS BACKUP. BACKUP is *not* a compression program. Do "help backup".

.bz2: bzip2 by Julian Seward (Burrows-Wheeler block sorting, see item 78)
http://www.muraroa.demon.co.uk/

.cab: Microsoft Cabinets
http://www.ddj.com/ftp/1997/1997.05/cabinet.zip
ftp://ftp.mv.com/pub/ddj/1997/1997.05/cabinet.zip

.cpt: Compact Pro for Mac and Power PC
ftp://wuarchive.wustl.edu/systems/mac/info-mac/cmp/

For Unix:
http://hyperarchive.lcs.mit.edu/HyperArchive/Archive/cmp/macutil-20b1-unix.shar
ftp://ftp.cwi.nl/pub/dik/macutil2.0b3.shar.Z

For DOS:
ftp://ftp.scruz.net/users/aladdin/public/
ftp://garbo.uwasa.fi/pc/arcers/

.ddi: files made by DiskDupe (Pro)
ftp://ftp.tem.nctu.edu.tw/Msdos/arcutil/unddi11u.zip
ftp://ftp.tem.nctu.edu.tw/Msdos/arcutil/x2file15.zip

.exe: self-extracting MSDOS executable (creates files on disk when run)
Run the file, or try unzip, lha or arj on it.

.exe: compressed MSDOS executable (decompresses itself in memory then runs
the decompressed code). To get the original uncompressed .exe:
ftp://garbo.uwasa.fi/pc/execomp/
To create such files:
ftp://ftp.simtel.net/pub/simtelnet/msdos/execomp/lzexe91e.zip
ftp://nic.funet.fi/pub/msdos/windows/util/winlite1.zip (for Windows)

.gif: gif files are images compressed with the LZW algorithm. See the
comp.graphics FAQ list for programs manipulating .gif files. See
suffix .Z below for source of LZW.

.gz, .z: gzip (or pack, see .z below). gzip uses the same algorithm as
zip 2.0x (see below); it can also extract packed and compressed files.
Contact: Jean-loup Gailly <support at gzip.org>
http://www.gzip.org

For Unix, MSDOS, OS/2, VMS, Atari, Amiga, Primos:
ftp://prep.ai.mit.edu/pub/gnu/ (.shar or .tar.gz: source)
ftp://prep.ai.mit.edu/pub/gnu/ (MSDOS self-extract)
ftp://ftp.simtel.net/pub/simtelnet/msdos/compress/gzip124.zip (MSDOS)
ftp://garbo.uwasa.fi/unix/arcers/ (source)
ftp://ftp.cdrom.com/pub/infozip/MSDOS/ (MSDOS exe)
ftp://ftp.cdrom.com/pub/infozip/WIN32/ (WIN95 & NT)
ftp://ftp.cdrom.com/pub/infozip/OS2/ (OS/2)
ftp://ftp.cdrom.com/pub/infozip/VMS/ (VMS exe)
ftp://ftp.cdrom.com/pub/infozip/UNIX/SUN/ (Solaris 2)
http://www.gzip.org/gzip123mvs.zip (MVS exe)

For Mac:
ftp://ivo.cps.unizar.es//Graficos/Public/SPDsoft/MacGzip_FAT_1.1.cpt.hqx
http://persephone.cps.unizar.es/general/gente/spd/gzip/ (MacGzip page)

.ha: ha 0.99 (improved PPMC - 4th order Markov modeling)
Contact: Harri Hirvola <harri.hirvola (AT) vaisala.infonet.com>
ftp://garbo.uwasa.fi/pc/arcers/
ftp://ftp.nl.net/gopher/NLnet-connected/aipnl/
ftp://sunsite.unc.edu/pub/Linux/utils/compress/ha0999p-linux.tar.gz

.hap: Hamarsoft HAP archiver (Markov modeling + arithmetic coding)
Contact: feldmann (AT) xs4all.nl or feldmann (AT) pi.net
ftp://garbo.uwasa.fi/pc/arcers/
http://www.xs4all.nl/~feldmann

.hpk: hpack (archiver with strong encryption)
Contact: Peter Gutmann <pgut1 (AT) cs.aukuni.ac.nz>
ftp://src.doc.ic.ac.uk/computing/archiving/compress/hpack/

.hqx: Macintosh BinHex format.. (BinHex is *not* a compression program,
it is similar to uuencode but handles multiple forks.)
for Mac:
ftp://mac.archive.umich.edu/mac/util/compression/

for Unix:
http://hyperarchive.lcs.mit.edu/HyperArchive/Archive/cmp/mcvert-216.shar

for MSDOS:
ftp://ftp.simtel.net/pub/simtelnet/msdos/mac/
ftp://garbo.uwasa.fi/pc/unix/

.jam: JAM real-time compressor for MSDOS
ftp://garbo.uwasa.fi/pc/arcers/

.lha:
.lzh: lha for MSDOS (LZ77 with a trie data structure, plus secondary static
Huffman coding on a block basis)
ftp://ftp.simtel.net/pub/simtelnet/msdos/arcers/lha255e.exe
ftp://garbo.uwasa.fi/pc/arcers/

lharc for Unix. (LZ77 with hash table and binary trees, plus secondary
Huffman coding). See lha for Unix below.
Warning: lharc can extract .lzh files created by
lharc 1.xx but not those created by lha.

lharc for VMS. Same warning as for Unix lharc.
ftp://wuarchive.wustl.edu/packages/compression/vax-vms/lharc.exe

lha for Unix.
ftp://oak.oakland.edu/pub/misc/unix/
ftp://garbo.uwasa.fi/unix/arcers/
Contact: lha-admin (AT) oki.co.jp or oki (AT) fs.telcom.oki.ac.jp

lha for Mac
ftp://wuarchive.wustl.edu/systems/mac/info-mac/cmp/

lha for Amiga
ftp://ftp.funet.fi/pub/amiga/utilities/archivers/
lha for OS/2:
ftp://hobbes.nmsu.edu/pub/os2/util/archiver/lh2_222.zip

MIME: see base64 above

.pak: pak for MSDOS (LZW algorithm)
ftp://ftp.simtel.net/pub/simtelnet/msdos/arcers/pak251.exe
ftp://garbo.uwasa.fi/pc/arcers/

.pit: PackIt (Macintosh)
for Mac:
http://hyperarchive.lcs.mit.edu/HyperArchive/Archive/cmp/stuffit-lite-35.hqx

for Unix:
http://hyperarchive.lcs.mit.edu/HyperArchive/Archive/cmp/mcvert-216.shar
ftp://garbo.uwasa.fi/mac/arcers/

.pp: PowerPacker (Amiga)
ftp://ftp.funet.fi/pub/amiga/fish/501-600/ff561/

.rar: RAR Contact: Eugene Roshal <roshal (AT) creabel.com>
or Andrey Spasibozhko <as (AT) hq.icb.chel.su>
http://www.creabel.com/softronic/
MSDOS:
ftp://ftp.simtel.net/pub/simtelnet/msdos/arcers/ rar*.exe
ftp://garbo.uwasa.fi/pc/arcers/ rar*.exe
ftp://ftp.kiae.su/msdos/arcers/ rar*.exe
ftp://ftp.elf.stuba.sk/pub/pc/pack/ *rar2*.exe
Unix:
ftp://ftp.kiae.su/pub/unix/arcers/ rar*.exe
Mac
ftp://wuarchive.wustl.edu/systems/mac/info-mac/cmp/
ftp://ftp.creabel.com/pub/rar/
Amiga (Unrar):
ftp://ftp.creabel.com/pub/rar/

.sea: self-extracting archive (Macintosh)
Run the file to extract it. The self-extraction code can be
removed with:
ftp://mac.archive.umich.edu/mac/utilities/compressionapps/
ftp://ftp.scruz.net/users/aladdin/public/ (MS Windows, .sit only)

.sdn: used by the Shareware Distribution Network.
Try the decompressors for .pak or .arj (see above)

.shar: Shell archive. This is not a compression program. Use "sh foo.shar"
to extract on Unix.
ftp://garbo.uwasa.fi/pc/unix/ (MSDOS)
ftp://wuarchive.wustl.edu/systems/mac/info-mac/cmp/ (Mac)

.sit: Stuffit for Macintosh
for Mac:
http://hyperarchive.lcs.mit.edu/HyperArchive/Archive/cmp/stuffit-lite-35.hqx

for Amiga:
ftp://ftp.funet.fi/pub/amiga/utilities/archivers/

for MSDOS:
ftp://ftp.scruz.net/users/aladdin/public/
ftp://garbo.uwasa.fi/pc/arcers/

.?q?: Squeeze for MSDOS (do not confuse with other 'squeeze' below).
Static Huffman coding.
ftp://ftp.simtel.net/pub/simtelnet/msdos/starter/ (squeeze)
ftp://ftp.simtel.net/pub/simtelnet/msdos/starter/ (unsqueeze)

.sqz: Squeeze for MSDOS (do not confuse with other 'squeeze' above)
LZ77 with hashing.
ftp://ftp.simtel.net/pub/simtelnet/msdos/arcers/sqz1083e.exe
ftp://garbo.uwasa.fi/pc/arcers/

.tar: tar is *not* a compression program. However, to be kind for you:
for MSDOS
ftp://ftp.simtel.net/pub/simtelnet/msdos/starter/
ftp://garbo.uwasa.fi/pc/unix/

for Unix
tar (you have it already. To extract: tar xvf file.tar)

for VMS
ftp://wuarchive.wustl.edu/packages/compression/vax-vms/tar.exe

for Macintosh
ftp://wuarchive.wustl.edu/systems/mac/info-mac/cmp/

for Amiga:
ftp://ftp.funet.fi/pub/amiga/fish/401-500/ff445/

.tar.Z, .tar-z, .taz: tar + compress
For Unix: zcat file.tar.Z | tar xvf -
with GNU tar: tar xvzf file.tar.Z
for MSDOS:
ftp://garbo.uwasa.fi/pc/unix/ (MSDOS exe)
ftp://ftp.kiae.su/msdos/arcers/tar*sr.zip (sources)
ftp://ftp.kiae.su/msdos/arcers/tar*_p.zip (MSDOS exe)
Other OS: first uncompress (see .Z below) then untar (see .tar above)

.tar.gz, .tgz, .tar-gz, .tar.z: tar + gzip
For Unix: gzip -cd file.tar.gz | tar xvf -
with GNU tar: tar xvzf file.tar.gz
for MSDOS:
ftp://ftp.simtel.net/pub/simtelnet/msdos/arcers/tar320g.zip
ftp://garbo.uwasa.fi/pc/unix/
for MSDOS, Windows 95, NT & OS/2:
ftp://garbo.uwasa.fi/pc/unix/
or http://till.home.ml.org/untgz.htm
for Windows 95 & Windows NT:
ftp://ftp.winzip.com/winzip/ or http://www.winzip.com

Other OS: first uncompress (see .gz above) then untar (see .tar above)

.td0: (compressed MS-DOS floppy image produced by TeleDisk)
ftp://ftp.simtel.net/pub/simtelnet/msdos/diskutil/teled212.zip

.uc2: UC2 for MSDOS and OS/2. (LZ77 with secondary static Huffman encoding on
a block basis, and dynamic dictionaries shared among files.)
Contact: desk (AT) aip.nl
ftp://garbo.uwasa.fi/pc/arcers/ (or uc2pro.exe)

.z: pack or gzip (see .gz above). pack uses static Huffman coding.
To extract, see .gz above.

.zip: pkzip 2.04g for MSDOS. (LZ77 with hashing, plus secondary static
Huffman coding on a block basis). Contact: support (AT) pkware.com
or http://www.pkware.com/
ftp://ftp.simtel.net/pub/simtelnet/msdos/zip/pkz204g.exe
ftp://garbo.uwasa.fi/pc/arcers/
ftp://ftp.simtel.net/pub/simtelnet/win95/compress/pk250w32.exe (WIN95)

arcutil 2.0 for VM/CMS (unzip only, not yet compatible with pkzip 2.04)
ftp://vmd.cso.uiuc.edu/public.477/arcutil.*

zip 1.1 for Unix, MSDOS, VMS, OS/2, ... (compatible with pkzip 1.10.
For corresponding unzip, see unzip 5.32 below).
ftp://ftp.cdrom.com/pub/infozip/src/

zip 2.2 and unzip 5.32 for Unix, MSDOS, VMS, OS/2, Amiga, ...
Compatible with pkzip 2.04g (LZ77 with hashing, plus secondary static
Huffman coding on a block basis). Contact: zip-bugs (AT) lists.wku.edu
See also http://infozip.cdrom.com/pub/infozip/
(On SGI, do not confuse with the editor also named 'zip'.)

ftp://ftp.cdrom.com/pub/infozip/src/ (source)
ftp://ftp.cdrom.com/pub/infozip/src/ (source)
ftp://ftp.cdrom.com/pub/infozip/MSDOS/ (MSDOS exe)
ftp://ftp.cdrom.com/pub/infozip/MSDOS/ (MSDOS exe)
ftp://ftp.cdrom.com/pub/infozip/WIN32/ (Win95 & NT)
ftp://ftp.cdrom.com/pub/infozip/WIN32/ (Win95 & NT)
[The Win95 version supports long file names; MSDOS version doesn't]
ftp://ftp.cdrom.com/pub/infozip/OS2/ (OS/2 exe 16&32 bit)
See also AMIGA, ATARI, MAC, UNIX, RISCOS, VMS... subdirectories.

ftp://ftp.icce.rug.nl/infozip/src/ (encryption source)

for Macintosh:
http://members.sitec.net/maczip/download/
ftp://mac.archive.umich.edu/mac/util/compression/
ftp://mac.archive.umich.edu/mac/util/compression/
ftp://ftp.cdrom.com/pub/infozip/MAC/
ftp://wuarchive.wustl.edu/systems/mac/info-mac/cmp/

WinZip by Nico Mak <support (AT) winzip.com> (uses Info-ZIP compress. code):
ftp://ftp.winzip.com/winzip/ or http://www.winzip.com (MS Windows)

.zoo: zoo 2.10 for MSDOS (algorithm copied from that of lha, see lha above)
ftp://ftp.simtel.net/pub/simtelnet/msdos/arcers/zoo210.exe
ftp://garbo.uwasa.fi/pc/arcers/

zoo 2.10 for Unix, VMS
ftp://oak.oakland.edu/pub/misc/unix/
ftp://garbo.uwasa.fi/unix/arcers/

zoo for Mac
ftp://mac.archive.umich.edu/mac/utilities/compressionapps/

zoo for Amiga
ftp://ftp.funet.fi/pub/amiga/utilities/archivers/

.??_: Microsoft compress.exe and expand.exe. compress.exe is available
in the Windows SDK (Software Development Kit) and in
ftp://ftp.microsoft.com/softlib/mslfiles/

.F: freeze for Unix (LZ77 with hashing, plus secondary dynamic Huffman
encoding)
ftp://wuarchive.wustl.edu/usenet/comp.sources.misc/volume35/freeze/
ftp://ftp.inria.fr/system/arch-compr/
Contact: Leonid A. Broukhis <leo (AT) zycad.com>

.Y: yabba for Unix, VMS, ... (Y coding, a variant of LZ78)
ftp://wuarchive.wustl.edu/usenet/comp.sources.unix/volume24/yabbawhap/
ftp://ftp.inria.fr/system/arch-compr/
Contact: Dan Bernstein <djb (AT) silverton.berkeley.edu>

.Z: compress for Unix ('the' LZW algorithm)
It is likely that your Unix system has 'compress' already. Otherwise:
ftp://wuarchive.wustl.edu/packages/compression/
(not in .Z format to avoid chicken and egg problem)

compress for MSDOS
ftp://ftp.simtel.net/pub/simtelnet/msdos/compress/comp430d.zip
ftp://garbo.uwasa.fi/pc/unix/
ftp://garbo.uwasa.fi/pc/source/comp430s.zip

compress for Macintosh
ftp://wuarchive.wustl.edu/systems/mac/info-mac/cmp/

compress for Amiga
ftp://ftp.funet.fi/pub/amiga/utilities/archivers/

compress for VAX/VMS
ftp://wuarchive.wustl.edu/packages/compression/vax-vms/lzcomp.exe
ftp://wuarchive.wustl.edu/packages/compression/vax-vms/lzdcmp.exe

--------------------------------------------------------------------------------

Subject: [3] What is the latest PKZIP version?

The latest official DOS version is 2.04g. The latest command line version
for Windows 95 is 2.50. The latest Windows 95 version is 2.70.
See http://www.pkware.com for more information.

Be warned that there are countless bogus PKZIP 1.20, 2.0, 2.02, 3.00B,
3.05, 4.1 and whatever scams floating around. They usually are hacks
of PKZIP 1.93A beta test version. Some of them are trojans and / or
carry computer viruses.

Note about pkzip 2.06 from a PKware employee:

Version 2.06 was released as an INTERNAL use only IBM version.
It is identical to 2.04G, but it has IBM names in the help
screens and such. That release is meant for IBM only.

If pkunzip indicates that you need version 2.8 to extract an
archive, your archive has been corrupted by a transfer not
made in binary mode (see item 30 below).
--------------------------------------------------------------------------------

Subject: [4] What is an archiver?


There is a distinction between archivers and other compression
programs:

- an archiver takes several input files, compresses them and produces
a single archive file. Examples are arc, arj, lha, zip, zoo.

- other compression programs create one compressed file for each
input file. Examples are freeze, yabba, compress, gzip. Such programs
are often combined with tar to create compressed archives (see
question 50: "What is this tar compression program?").

For a comparison of zip and gzip, see the gzip README file. (In short:
zip is an archiver, gzip is not; only zip is compatible with pkzip.)

--------------------------------------------------------------------------------

Subject: [5] What is the best general purpose compression program?


The answer is: it depends. (You did not expect a definitive answer,
did you?)

It depends whether you favor speed, compression ratio, a standard and
widely used archive format, the number of features, etc... Just as
for text editors, personal taste plays an important role. compress has
4 options, arj 2.30 has about 130 options; different people like
different programs. *Please* do not start or continue flame wars on
such matters of taste.

Several benchmarks of MSDOS archivers are available:
- ftp://ftp.simtel.net/pub/simtelnet/msdos/arcers/actest*.zip
and http://www.geocities.com/SiliconValley/Park/4264/act.html
by Jeff Gilchrist <jeffg (AT) cips.ca>
- ftp://garbo.uwasa.fi/pc/arcers/
by Jonathan Burt <jonathan (AT) jaburt.demon.co.uk>

Please do not post your own benchmarks made on your own files that
nobody else can access. If you think that you must absolutely post yet
another benchmark, make sure that your test files are available by
anonymous ftp.

Since all other benchmarks are for MSDOS only, here is one mainly for
Unix, on a 33Mhz Compaq 386. All programs have been run on Unix SVR4,
except pkzip and arj which only run on MSDOS.

The programs compared here were chosen because they are the most
popular or because they run on Unix and source is available. For ftp
information, see above. Three programs (hpack, comp-2 and ha) have
been added because they achieve better compression (at the expense of
speed) and one program (lzrw3-a) has been added because it favors
speed at the expense of compression:

- comp-2 is in ftp://ftp.coast.net/pub/Coast/disk2/msdos/ddjmag/
(inner zip file nelson.zip),
- hpack is in ftp://garbo.uwasa.fi/unix/arcers/
- ha 0.98 is in ftp://garbo.uwasa.fi/pc/arcers/
- lzrw3-a is in http://wwwvms.utexas.edu/~cbloom/src/lzrw.zip

The 14 files used in the comparison are from the standard Calgary
Text Compression Corpus, available in
ftp://ftp.cpsc.ucalgary.ca/pub/projects/text.compression.corpus/

The whole corpus includes 18 files, but the 4 files paper[3-6] are
generally omitted in benchmarks. It contains several kinds of file
(ascii, binary, image, etc...) but has a bias towards large files.
You may well get different ratings on the typical mix of files that
you use daily, so keep in mind that the comparisons given below are
only indicative.

The programs are ordered by decreasing total compressed size. For a
fair comparison between archivers and other programs, this size is
only the size of the compressed data, not the archive size.

The programs were run on an idle machine, so the elapsed time
is significant and can be used to compare Unix and MSDOS programs.

[Note: These benchmarks are now *very* old. I have to do them again
on more recent hardware with the latest programs. For recent results
on MSDOS, check http://www.geocities.com/SiliconValley/Park/4264/act.html ]

size lzrw3a compress lharc yabba pkzip freeze
version: 4.0 1.02 1.0 1.10 2.3.5
options: -m300000
------ ----- ------ ------ ------ ------ ------
bib 111261 49040 46528 46502 40456 41354 41515
book1 768771 416131 332056 369479 306813 350560 344793
book2 610856 274371 250759 252540 229851 232589 230861
geo 102400 84214 77777 70955 76695 76172 68626
news 377109 191291 182121 166048 168287 157326 155783
obj1 21504 12647 14048 10748 13859 10546 10453
obj2 246814 108040 128659 90848 114323 90130 85500
paper1 53161 24522 25077 21748 22453 20041 20021
paper2 82199 39479 36161 35275 32733 32867 32693
pic 513216 111000 62215 61394 65377 63805 53291
progc 39611 17919 19143 15399 17064 14164 14143
progl 71646 24358 27148 18760 23512 17255 17064
progp 49379 16801 19209 12792 16617 11877 11686
trans 93695 30292 38240 28092 31300 23135 22861
3,141,622 1,400,105 1,259,141 1,200,580 1,159,340 1,141,821 1,109,290
real 0m35s 0m59s 5m03s 2m40s 5m27s
user 0m25s 0m29s 4m29s 1m46s 4m58s
sys 0m05s 0m10s 0m07s 0m18s 0m08s
MSDOS: 1m39s


zoo lha arj pkzip zip hpack comp-2 ha
2.10 1.0(Unix) 2.30 2.04g 1.9 0.75a 0.98
ah 2.13(MSDOS) -jm -ex -6 a2
------ ------ ------ ------ ------- ------ ------ ------
bib 40742 40740 36090 35126 34950 35619 29840 26927
book1 339076 339074 318382 312490 312619 306876 237380 235733
book2 228444 228442 210521 206513 206306 208486 174085 163535
geo 68576 68574 69209 68706 68418 58976 64590 59356
news 155086 155084 146855 144545 144395 141608 128047 123335
obj1 10312 10310 10333 10306 10295 10572 10819 9799
obj2 84983 84981 82052 81132 81336 80806 85465 80381
paper1 19678 19676 18710 18531 18525 18607 16895 15675
paper2 32098 32096 30034 29568 29674 29825 25453 23956
pic 52223 52221 53578 52409 55051 51778 55461 51639
progc 13943 13941 13408 13341 13238 13475 12896 11795
progl 16916 16914 16408 16122 16175 16586 17354 15298
progp 11509 11507 11308 11200 11182 11647 11668 10498
trans 22580 22578 20046 19462 18879 20506 21023 17927
1,096,166 1,096,138 1,036,934 1,019,451 1,021,043 1,005,367 890,976 845,854
real 4m07s 6m03s 1m49s 1h22m17s 27m05s
user 3m47s 4m23s 1m43s 1h20m46s 19m27s
sys 0m04s 0m08s 0m02s 0m12s 2m03s
MSDOS: 1m49s 2m41s 1m43s 14m43s

Notes:

- the compressed data for 'zoo ah' is always two bytes longer than for
lha. This is simply because both programs are derived from the same
source (ar002, written by Haruhiko Okumura, available by ftp in
ftp://ftp.simtel.net/pub/simtelnet/msdos/arcers/ar002.zip).

- hpack 0.75a gives slightly different results on SunOS. (To be checked
with latest version of hpack).

- the MSDOS versions are all optimized with assembler code and were run
on a RAM disk. So it is not surprising that they often go faster than
their Unix equivalent.

--------------------------------------------------------------------------------

Subject: [7] Which books should I read?


[BWC 1989] Bell, T.C, Cleary, J.G. and Witten, I.H, "Text Compression",
Prentice-Hall 1989. ISBN: 0-13-911991-4. Price: approx. US$60
The reference on text data compression.

[Nel 1996] Mark Nelson & Jean-loup Gailly, "The Data Compression Book",
2nd edition. M&T Books, New York, NY 1996. ISBN 1-55851-434-1
541 pages. List price in the US is $39.95 including one PC-compatible
disk bearing all the source code printed in the book.
A practical introduction to data compression.
The book is targeted at a person who is comfortable reading C code but
doesn't know anything about data compression. Its stated goal is to get
you up to the point where you are competent to program standard
compression algorithms.

[Will 1990] Williams, R. "Adaptive Data Compression", Kluwer Books, 1990.
ISBN: 0-7923-9085-7. Price: US$75.
Reviews the field of text data compression and then addresses the
problem of compressing rapidly changing data streams.

[Stor 1988] Storer, J.A. "Data Compression: Methods and Theory", Computer
Science Press, Rockville, MD. ISBN: 0-88175-161-8.
A survey of various compression techniques, mainly statistical
non-arithmetic compression and LZSS compression. Includes complete Pascal
code for a series of LZ78 variants.

[Stor 1992] Storer, J.A. "Image and Text Compression", Kluwer Academic
Publishers, 1992, ISBN 0-7923-9243-4

[Say 1996] Sayood, Khalid. "Introduction to Data Compression",
San Francisco: Morgan Kaufmann Publishers, 1996. ISBN 1-55860-346-8;
US&Canada $64.95. More info in http://www.mkp.com/pages/3468/index.html
The book covers both lossy and lossless compression techniques and their
applications to image, speech, text, audio, and video compression.

[HHJ 1997] Darrel Hankerson, Greg A. Harris, and Peter D. Johnson Jr.
"Introduction to Information Theory and Data Compression", 1997.
ISBN 0-8493-3985-5 http://www.dms.auburn.edu/compression/

[DS 1997] David Salomon, "Data Compression: The Complete Reference"
Springer, 1997, ISBN 0-387-98280-9. Price: US$ 39.95.

[BK 95] Bhaskaran V. and Konstantinides K., "Image and Video Compression
Standards: Algorithms and Architectures", Kluwer Academic Publishers, 1995.
ISBN 0-7923-9591-3

[ACG 1991] Advances in Speech Coding, edited by Atal, Cuperman, and Gersho,
Kluwer Academic Press, 1991.

[GG 1991] Vector Quantization and Signal Compression, by Gersho and Gray,
Kluwer Acad. Press, 1991, ISBN 0-7923-9181-0.

[CT 1991] Elements of Information Theory, by T.M.Cover and J.A.Thomas
John Wiley & Sons, 1991. ISBN 0-471-06259-6.

Review papers:

[BWC 1989] Bell, T.C, Witten, I.H, and Cleary, J.G. "Modeling for Text
Compression", ACM Computing Surveys, Vol.21, No.4 (December 1989), p.557
A good general overview of compression techniques (as well as modeling for
text compression); the condensed version of "Text Compression".

[Lele 1987] Lelewer, D.A, and Hirschberg, D.S. "Data Compression", ACM
Computing Surveys, Vol.19, No.3 (September 1987), p.261.
A survey of data compression techniques which concentrates on Huffman
compression and makes only passing mention of other techniques.


Bibliographies for Image Compression are available at
http://www.dip.ee.uct.ac.za/~brendt/bibliographies/


--------------------------------------------------------------------------------

Subject: [8] What about patents on data compression algorithms?


[Note: the appropriate group for discussing software patents is
comp.patents or misc.legal.computing, not comp.compression.]

Only a very small subset of all patents on data compression are mentioned
here; there are several hundred patents on lossless data compression alone.
All patents mentioned here are US patents, and thus probably not applicable
outside the US. The abstracts and claims of all recent US patents can be
obtained from http://patent.womplex.ibm.com/
See item 70, "Introduction to data compression" for the
meaning of LZ77, LZ78 or LZW.


(a) Run length encoding

- Tsukiyama has two patents on run length encoding: 4,586,027 and 4,872,009
granted in 1986 and 1989 respectively. The first one covers run length
encoding in its most primitive form: a length byte followed by the
repeated byte. The second patent covers the 'invention' of limiting the
run length to 16 bytes and thus the encoding of the length on 4 bits.
Here is the start of claim 1 of patent 4,872,009, just for pleasure:

1. A method of transforming an input data string comprising a plurality
of data bytes, said plurality including portions of a plurality of
consecutive data bytes identical to one another, wherein said data
bytes may be of a plurality of types, each type representing different
information, said method comprising the steps of: [...]

- O'Brien has patented (4,988,998) run length encoding followed by LZ77.


(b) LZ77

- Waterworth patented (4,701,745) the algorithm now known as LZRW1,
because Ross Williams reinvented it later and posted it on
comp.compression on April 22, 1991. (See item 5 for the ftp site
with all LZRW derivatives.) The *same* algorithm has later been
patented by Gibson & Graybill (see below). The patent office failed
to recognize that the same algorithm was patented twice, even though
the wording used in the two patents is very similar.

The Waterworth patent is now owned by Stac Inc, which won a lawsuit
against Microsoft, concerning the compression feature of MSDOS 6.0.
Damages awarded were $120 million. (Microsoft and Stac later
settled out of court.)

- Fiala and Greene obtained in 1990 a patent (4,906,991) on all
implementations of LZ77 using a tree data structure. Claim 1 of the
patent is much broader than the algorithms published by Fiala and
Greene in Comm.ACM, April 89. The patent covers the algorithm
published by Rodeh and Pratt in 1981 (J. of the ACM, vol 28, no 1,
pp 16-24). It also covers the algorithms used in lharc, lha and zoo.

- Notenboom (from Microsoft) 4,955,066 uses three levels of
compression, starting with run length encoding.

- The Gibson & Graybill patent 5,049,881 covers the LZRW1 algorithm
previously patented by Waterworth and reinvented by Ross Williams.
Claims 4 and 12 are very general and could be interpreted as
applying to any LZ algorithm using hashing (including all variants
of LZ78):

4. A compression method for compressing a stream of input data into
a compressed stream of output data based on a minimum number of
characters in each input data string to be compressed, said
compression method comprising the creation of a hash table, hashing
each occurrence of a string of input data and subsequently searching
for identical strings of input data and if such an identical string
of input data is located whose string size is at least equal to the
minimum compression size selected, compressing the second and all
subsequent occurrences of such identical string of data, if a string
of data is located which does not match to a previously compressed
string of data, storing such data as uncompressed data, and for each
input strings after each hash is used to find a possible previous
match location of the string, the location of the string is stored
in the hash table, thereby using the previously processed data to
act as a compression dictionary.

Claim 12 is identical, with 'method' replaced with 'apparatus'. Since
the 'minimal compression size' can be as small as 2, the claim could
cover any dictionary technique of the LZ family. However the text of the
patent and the other claims make clear that the patent should cover the
LZRW1 algorithm only. (In any case the Gibson & Graybill patent is likely
to be invalid because of the prior art in the Waterworth patent.)

- Phil Katz, author of pkzip, also has a patent on LZ77 (5,051,745)
but the claims only apply to sorted hash tables, and when the hash
table is substantially smaller than the window size.

- IBM patented (5,001,478) the idea of combining a history buffer (the
LZ77 technique) and a lexicon (as in LZ78).

- Stac Inc patented (5,016,009 and 5,126,739) yet another variation of LZ77
with hashing. The '009 patent was used in the lawsuit against Microsoft
(see above). Stac also has a patent on LZ77 with parallel lookup in
hardware (5,003,307).

- Robert Jung, author of 'arj', has been granted patent 5,140,321 for one
variation of LZ77 with hashing. This patent is very close to the
LZRW3-A algorithm, also previously discovered by Ross Williams. LZRW3-A was
posted on comp.compression on July 15, 1991. The patent was filed two months
later on Sept 4, 1991. Microsoft has patented a similar idea (two level
table with pseudo-LRU managment of slots inside the level-2 table) in
5,455,577 (filed in 1993).

- Chambers 5,155,484 is yet another variation of LZ77 with hashing.
The hash function is just the juxtaposition of two input bytes,
this is the 'invention' being patented. The hash table is named
'direct lookup table'.


(c) LZ78

- One form of the original LZ78 algorithm was patented (4,464,650) by
its authors Lempel, Ziv, Cohn and Eastman. This patent is owned
by Unisys.


- The LZW algorithm used in 'compress' is patented by IBM (4,814,746)
and Unisys (4,558,302). It is also used in the V.42bis compression
standard (see question 11 on V.42bis below), in Postscript Level 2, in
GIF and TIFF. Unisys sells the license to modem manufacturers for a
onetime fee (contact: Welch Patent Desk, Unisys Corp., P.O. Box 500,
Bluebell, PA 19424 Mailcode C SW 19). CompuServe is licensing the
usage of LZW in GIF products for 1.5% of the product price, of which
1% goes to Unisys; usage of LZW in non-GIF products must be licensed
directly from Unisys. For more information, see http://www.unisys.com/
or email to lzw_info (AT) unisys.com.

The IBM patent application was first filed three weeks before that of
Unisys, but the US patent office failed to recognize that they
covered the same algorithm. (The IBM patent is more general, but its
claim 7 is exactly LZW.)

- Klaus Holtz also claims that patent 4,366,551 for his "autosophy"
data compression method covers LZ78 and LZW. According to Holtz, most of
the largest V.42bis modem manufacturers have paid for patent licenses.

- AP coding is patented by Storer (4,876,541). (Get the yabba package
for source code, see question 2 above, file type .Y) Storer also
claims that his patent covers V.42bis.


(d) arithmetic coding

- IBM holds many patents on arithmetic coding (4,122,440 4,286,256 4,295,125
4,463,342 4,467,317 4,633,490 4,652,856 4,792,954 4,891,643 4,901,363
4,905,297 4,933,883 4,935,882 5,045,852 5,099,440 5,142,283 5,210,536
5,414,423 5,546,080). It has patented in particular the Q-coder
implementation of arithmetic coding. The JBIG standard, and the arithmetic
coding option of the JPEG standard requires use of the patented algorithm.
No JPEG-compatible method is possible without infringing the patent, because
what IBM actually claims rights to is the underlying probability model (the
heart of an arithmetic coder). (See item 75 for details.)

See also below details on many other patents on arithmetic coding (4,973,961
4,989,000 5,023,611 5,025,258 5,272,478 5,307,062 5,309,381 5,311,177
5,363,099 5,404,140 5,406,282 5,418,532). The list is not exhaustive.


(e) predictor

- The 'predictor' algorithm was first described in the paper

Raita, T. and Teuhola, J. (1987), "Predictive text compression by hashing",
ACM Conference on Information Retrieval

This algorithm has been patented (5,229,768) by K. Thomas in 1993. It
is used in the Internet Draft "PPP Predictor Compression Protocol" (see
ftp://venera.isi.edu/internet-drafts/).

(f) compression of random data

- The US patent office no longer grants patents on perpetual motion machines,
but has recently granted a patent on a mathematically impossible process
(compression of truly random data): 5,533,051 "Method for Data Compression".
See item 9.5 of this FAQ for details.


As can be seen from the above list, some of the most popular compression
programs (compress, pkzip, zoo, lha, arj) are now covered by patents.
(This says nothing about the validity of these patents.)

Here are some references on data compression patents. Some of them are
taken from the list ftp://prep.ai.mit.edu/pub/lpf/patent-list.

3,914,586
Data compression method and apparatus
filed 10/25/73, granted 10/21/75
General Motors Corporation, Detroit MI
Duane E. McIntosh, Santa Ynez CA
Data compression apparatus is disclosed is operable in either a bit
pair coding mode of a word coding mode depending on the degree of
redundancy of the data to be encoded.

3,976,844
Data communication system for transmitting data in compressed form
filed Apr. 4, 1975, granted Aug. 24, 1976
inventor Bernard K. Betz, assignee Honeywell Information Systems, Inc.
[encode differences with previous line]

4,021,782
Data compaction system and apparatus
inventor Hoerning
filed 04/30/1975, granted 05/03/1977
[A primitive form of LZ77 with implicit offsets (compare with previous record)]

4,054,951
Data expansion apparatus
inventor R.D. Jackson, assignee IBM
filed Jun. 30, 1976, granted Oct. 18, 1977
[Covers only decompression of data compressed with a variant of LZ77.]

4,087,788
Data compression system
filed 1/14/77, granted 5/2/78
NCR Canada LTD - NCR Canada Ltee, Mississauga CA
Brian J. Johannesson, Waterloo CA
A data compression system is disclosed in which the left hand boundary
of a character is developed in the form of a sequence of Freeman
direction codes, the codes being stored in digital form within a
processor.

4,122,440
Method and means for arithmetic string coding
assignee IBM
filed 1977/03/04, granted 1978/10/24
[This is the basic idea of arithmetic coding. Note that the patent is
expired now.]

4,286,256
Method and means for arithmetic coding using a reduced number of operations.
granted Aug 25, 1981
assignee IBM

4,295,125
A method and means for pipeline decoding of the high to low order pairwise
combined digits of a decodable set of relatively shifted finite number of
strings
granted Oct 13, 1981
assignee IBM

4,366,551
Associative Memory Search System
filed June 16, 1975, granted Dec. 28, 1982.
inventor Klaus Holtz, assignee Omni Dimensional Networks.

4,412,306
System for minimizing space requirements for storage and transmission of
digital signals
filed May 14, 1981, granted Oct. 25, 1983
inventor Edward W. Moll

4,463,342
A method and means for carry-over control in a high order to low order
combining of digits of a decodable set of relatively shifted finite number
strings.
granted Jul 31, 1984
assignee IBM

4,491,934
Data compression process
filed May 12, 1982, granted Jan. 1, 1985
inventor Karl E. Heinz

4,464,650
Apparatus and method for compressing data signals and restoring the
compressed data signals
inventors Lempel, Ziv, Cohn, Eastman
assignee Sperry Corporation (now Unisys)
filed 8/10/81, granted 8/7/84
A compressor parses the input data stream into segments where each
segment comprises a prefix and the next symbol in the data stream
following the prefix. [This is the original LZ78 algorithm.]

4,467,317
High-speed arithmetic compression using using concurrent value updating.
granted Aug 21, 1984
assignee IBM

4,494,108
Adaptive source modeling for data file compression within bounded memory
filed Jun. 5, 1984, granted Jan. 15, 1985
invntors Glen G. Langdon, Jorma J. Rissanen
assignee IBM
order 1 Markov modeling

4,558,302
High speed data compression and decompression apparatus and method
inventor Welch
assignee Sperry Corporation (now Unisys)
filed 6/20/83, granted 12/10/85
re-examined: filed 12/14/92, granted 4/1/94.
The text of the original 1985 patent can be ftped from
ftp://ftp.uni-stuttgart.de/pub/doc/comp-patents/US4558302.Z
There is also a European Patent 0,129,439 1/2/89 for DE, FR, GB, IT
and patent pending for Japan.

4,560,976
Data compression
filed 6/5/84, granted 12/24/85
Codex Corporation, Mansfield MA
Steven G. Finn, Framingham, MA
A stream of source characters, which occur with varying relative
frequencies, is encoded into a compressed stream of codewords, each
having one, two or three subwords, by ranking the source characters by
their current frequency of appearance, encoding the source characters
having ranks no higher than a first number as one subword codewords,
source characters having ranks higher than the first number but no
higher than a second number as two subword codewords, and the
remaining source characters as three subword codewords.

4,586,027
Method and system for data compression and restoration
inventor Tsukimaya et al.
assignee Hitachi
filed 08/07/84, granted 04/29/86
patents run length encoding

4,597,057
System for compressed storate of 8-bit ascii bytes using coded strings
of 4-bit nibbles.
inventor Snow, assignee System Development corporation.
filed 12/31/1981, granted 06/24/1986.
Compression using static dictionary of common words, prefixes and suffixes.

4,612,532
Data compression apparatus and method
inventor Bacon, assignee Telebyte Corportion
filed Jun. 19, 1984, granted Sep. 16, 1986
[Uses followsets as in the pkzip 0.92 'reduce' algorithm, but the
followsets are dynamically updated. This is in effect a sort of order-1
Markov modeling.]

4,622,545
Method and apparatus for image compression and Manipulation
inventor William D. Atkinson
assignee Apple computer Inc.
filed 9/30/82
granted 11/11/86

4,633,490
Symmetrical adaptive data compression/decompression system.
granted Dec 30, 1985
assignee IBM

4,652,856
A multiplication-free multi-alphabet arithmetic code.
granted Feb 4, 1986
assignee IBM

4,667,649
Data receiving apparatus
filed 4/18/84, granted 6/30/87
inventors Kunishi et al.
assignee Canon Kabushiki Kaisha, Tokyo Japan
compression of Fax images.

4,682,150
Data compression method and apparatus
inventors Mathes and Protheroe,
assignee NCR Corporation, Dayton OH
A system and apparatus for compressing redundant and nonredundant
binary data generated as part of an operation of a time and attendance
terminal in which the data represents the time an employee is present
during working hours.

4,701,745
Data compression system
inventor Waterworth John R
assignee Ferranti PLC GB, patent rights now acquired by Stac Inc.
filed 03/03/1986 (03/06/1985 in GB), granted 10/20/1987
Algorithm now known as LZRW1 (see above)
I claim:
1. A data compression system comprising an input store for receiving
and storing a plurality of bytes of uncompressed data from an outside
source, and data processing means for processing successive bytes of
data from the input store;
the data processing means including circuit means operable to check
whether a sequence of successive bytes to be processed identical with
a sequence of bytes already processed, and including hash generating
means responsive to the application of a predetermined number of
bytes in sequence to derive a hash code appropriate to those bytes, a
temporary store in which the hash code may represent the address of a
storage location, and a pointer counter operable to store in the
temporary store at said address a pointer indicative of the position
in the input store of one of the predetermined number of bytes;
output means operable to apply to a transfer medium each byte of data
not forming part of such an identical sequence; and
encoding means responsive to the identification of such a sequence to
apply to the transfer medium an identification signal which identifies
both the location in the input store of the previous occurrence of the
sequence of bytes and the number of bytes contained in the sequence.

4,730,348
Adaptive data compression system
inventor MacCrisken, assignee Adaptive Computer Technologies
filed Sep. 19, 1986, granted Mar. 8, 1988
[order-1 Markov modeling + Huffman coding + LZ77]

4,758,899
Data compression control device
inventor Tsukiyama, assignee Hitachi
filed 11/20/1985, granted 07/19/1988
Limits compression to ensure that tape drive stays busy.

4,792,954
Concurrent detection of errors in arithmetic data compression coding
assignee IBM
filed 1986/10/31, granted 1988/12/20

4,809,350
Data compression system
filed Jan. 30, 1987, granted Feb. 28, 1989
inventor Yair Shimoni & Ron Niv
assignee Elscint Ltd., Haifa, Israel
[Image compression via variable length encoding of differences with
predicted data.]

4,814,746
Data compression method
inventors Victor S. Miller, Mark N. Wegman
assignee IBM
filed 8/11/86, granted 3/21/89
A previous application was filed on 6/1/83, three weeks before the
application by Welch (4,558,302)
Communications between a Host Computing System and a number of remote
terminals is enhanced by a data compression method which modifies the
data compression method of Lempel and Ziv by addition of new character
and new string extensions to improve the compression ratio, and
deletion of a least recently used routine to limit the encoding tables
to a fixed size to significantly improve data transmission efficiency.

4,841,092
continued in 5,003,307

4,853,696
Code converter for data compression/decompression
filed 4/13/87, granted 8/1/89
inventor Amar Mukherjee, Maitland FL
assignee University of Central Florida, Orlando FL
Another hardware Huffman encoder:
A code converter has a network of logic circuits connected in reverse
binary tree fashion with logic paths between leaf nodes and a common
root node.

4,872,009
Method and apparatus for data compression and restoration
inventor Tsukimaya et al.
assignee Hitachi
filed 12/07/87, granted 10/03/89
This patent on run length encoding covers the 'invention' of limiting
the run length to 16 bytes and thus the encoding of the length on 4 bits.

4,876,541
Stem [sic] for dynamically compressing and decompressing electronic data
filed 10/15/87, granted 10/24/89
inventor James A. Storer
assignee Data Compression Corporation
A data compression system for encoding and decoding textual data,
including an encoder for encoding the data and for a decoder for
decoding the encoded data.

4,891,643
Arithmetic coding data compression/de-compression by selectively
employed, diverse arithmetic encoders and decoders.
file 1986/09/15, granted 1990/01/02
assignee IBM

4,901,363
System for compressing bi-level data
assignee IBM
[arithmetic coding]

4,905,297
Arithmetic coding encoder and decoder system.
granted Feb 27, 1990
assignee IBM

4,906,991
Textual substitution data compression with finite length search window
filed 4/29/1988, granted 3/6/1990
inventors Fiala,E.R., and Greene,D.H.
assignee Xerox Corporation
extended in 5,058,144

4,933,883
Probability adaptation for arithmetic coders.
granted Jun 12, 1990
assignee IBM

4,935,882
Probability adaptation for arithmetic coders.
granted Jun 19, 1990
assignee IBM

4,941,193
Barnsley, fractal compression.

4,943,869
Compression Method for Dot Image Data
filed 1988-05-04, granted 1990-07-24
assignee Fuji Photo Film Co.
Lossy and lossless image compression schemes.

4,955,066
Compressing and Decompressing Text Files
filed 10/13/89, granted 09/04/90
inventor Notenboom, L.A.
assignee Microsoft
Now extended as 5,109,433
[Noted in signon screen of Word 5.5 and on the outside of the MS-DOS 5.0
Upgrade.]
A method of compressing a text file in digital form is disclosed.
A full text file having characters formed into phrases is provided by an
author. The characters are digitally represented by bytes. A first pass
compression is sequentially followed by a second pass compression of the
text which has previously been compressed. A third or fourth level of
compression is serially performed on the compressed text. For example, in
a first pass, the text is run-length compressed. In a second pass, the
compressed text is further compressed with key phrase compression. In a
third pass, the compressed text is further compressed with Huffman
compression. The compressed text is stored in a text file having a Huffman
decode tree, a key phrase table, and a topic index. The data is
decompressed in a single pass and provided one line at a time as an output.
Sequential compressing of the text minimizes the storage space required for
the file. Decompressing of the text is performed in a single pass. As a
complete line is decompressed, it is output rapidly, providing full text to
the user.

4,973,961
Method and apparatus for carry-over control in arithmetic coding.
granted Nov 27, 1990
assignee AT&T

4,988,998
Data compression system for successively applying at least two data
compression methods to an input data stream.
inventor O'Brien
assignee Storage Technology Corporation, Louisville, Colorado
filed Sep 5, 1989, granted Jan 29, 1991.
Run length encoding followed by LZ77.

4,989,000
Data string compression using arithmetic encoding with simplified probability
subinterval estimation
filed 1989/06/19, granted 1991/01/29]
[shift & add instead of multiply]

5,001,478
Method of Encoding Compressed Data
filed 12/28/89, granted 03/19/91
inventor Michael E. Nagy
assignee IBM
1. A method of encoding a compressed data stream made up of a sequence of
literal references, lexicon references and history references, which
comprises the steps of:
assigning to each literal reference a literal identifier;
assigning to each history reference a history identifier;
assigning to each lexicon reference a lexicon identifier;
and emitting a data stream with said identifiers assigned to said references.
Gordon Irlam <gordoni (AT) cs.adelaide.edu.au> says:
The invention can probably be best understood by considering the
decompressor. It consists of a history buffer, and a lexicon buffer, both
of which are initially empty. The history buffer contains the last n
symbols emitted. Whenever a history buffer reference is to be output the
string so referenced is subsequently moved to the lexicon buffer for future
reference. Thus the history buffer keeps track of strings that may be
repeated on a very short term basis, while the lexicon buffer stores items
for a longer time. Furthermore a history reference involves specifying
both the offset and length within the history buffer, whereas a lexicon
reference simply specifies a number denoting the string. Both buffers have
a finite size.

5,003,307
Data compression apparatus with shift register search means
filed Oct. 6, 1989, granted Mar. 26, 1991
inventors George Glen A, Ivey Glen E, Whiting Douglas L
assignee Stac Inc
continuation of 4,841,092

5,016,009
Data compression apparatus and method
filed 01/13/1989, granted 05/14/1991
inventors George Glen A, Ivey Glen E, Whiting Douglas L
assignee Stac Inc
LZ77 with offset hash table (extended in 5,126,739)

5,023,611
Entropy encoder/decoder including a context extractor.
granted Jun 11, 1991
assignee AT&T

5,025,258
Adaptive probability estimator for entropy encoder/decoder.
granted Jun 18, 1991
assignee AT&T

5,045,852
Dynamic model selection during data compression
assignee IBM
[arithmetic coding]

5,049,881
Apparatus and method for very high data rate-compression incorporating
lossless data compression and expansion utilizing a hashing technique
inventors Dean K. Gibson, Mark D. Graybill
assignee Intersecting Concepts, Inc.
filed 6/18/90, granted 9/17/91
[covers lzrw1, almost identical with Waterworth 4,701,745]

5,051,745
String searcher, and compressor using same
filed 8/21/90, granted 9/24/91
inventor Phillip W. Katz (author of pkzip)
In the string search method and apparatus pointers to the string to be
searched are indexed via a hashing function and organized according to the
hashing values of the string elements pointed to. The hashing function is
also run on the string desired to be found, and the resulting hashing value
is used to access the index. If the resulting hashing value is not in the
index, it is known that the target string does not appear in the string
being searched. Otherwise the index is used to determine the pointers which
correspond to the target hashing value, these pointers pointing to likely
candidates for matching the target string. The pointers are then used to
sequentially compare each of the locations in the string being searched to
the target string, to determine whether each location contains a match to
the target string.
In the method and apparatus for compressing a stream of data symbols, a
fixed length search window, comprising a predetermined contiguous portion
of the symbol stream, is selected as the string to be searched by the
string searcher. If a string to be compressed is found in the symbol
stream, a code is output designating the location within the search window
of the matching string and the length of the matching string.

5,065,447 (continued in 5,347,600)
Method and apparatus for processing digital data
filed Jul. 5, 1989, granted Nov. 12, 1991
inventors Michael F. Barnsley and Alan D. Sloan
[Patents image compression with the "Fractal Transform"]

5,099,440
Probability adaptation for arithmetic coders

5,109,433
Compressing and decompressing text files
inventor Notenboom
assignee Microsoft
extension of 4,955,066

5,126,739
Data Compression Apparatus and Method
filed Nov. 27, 1990, granted June 30, 1992.
inventor Whiting et. al
assignee Stac Inc
LZ77 with offset hash table (extension of 5,016,009)

5,140,321
Data compression/decompression method and apparatus
filed 9/4/91, granted 8/18/92
inventor Robert Jung
assignee Prime Computer

5,142,283
Arithmetic compression coding using interpolation for ambiguous symbols
filed 1990/07/10, granted 1992/08/25
assignee IBM

5,155,484
Fast data compressor with direct lookup table indexing into history buffer
filed 9/13/1991, granted 10/13/1992
inventor Chambers, IV, Lloyd L., Menlo Park, California
assignee Salient Software, Inc., Palo Alto, California (02)
Uses a 64K hash table indexed by the first two characters of
the input string. Includes several claims on the LZ77 file format
(literal or pair offset,length).

5,179,378
file Jul. 30, 1991, granted Jan. 12, 1993
inventor Ranganathan
assignee University of South Florida
Method and apparatus for the compression and decompression of data
using Lempel-Ziv based techniques.
[This covers LZ77 hardware compression with a systolic array of
processors working in parallel.]

5,210,536
Data compression/coding method and device for implementing said method
assignee IBM
[PPM + arithmetic coding]

5,229,768
Adaptive data compression system
granted Jul. 20, 1993
inventor Kasman E. Thomas
assignee Traveling Software, Inc.
A system for data compression and decompression is disclosed. A series of
fixed length overlapping segments, called hash strings, are formed from an
input data sequence. A retrieved character is the next character in the input
data sequence after a particular hash string. A hash function relates a
particular hash string to a unique address in a look-up table (LUT). An
associated character for the particular hash string is stored in the LUT at
the address. When a particular hash string is considered, the content of the
LUT address associated with the hash string is checked to determine whether
the associated character matches the retrieved character following the hash
string. If there is a match, a Boolean TRUE is output; if there is no match,
a Boolean FALSE along with the retrieved character is output. Furthermore, if
there is no match, then the LUT is updated by replacing the associated
character in the LUT with the retrieved character. [...]
[This algorithm is used in the Internet draft
"PPP Predictor Compression Protocol".]

5,272,478
Method and apparatus for entropy coding
assignee Ricoh
[arithmetic coding with finite state machine]

5,307,062
Coding system
filed 1992/12/15, granted 1994/04/26
assignee Mitsubishi
[binary arithmetic coding, see also 5,404,140]

5,309,381
Probability estimation table apparatus
filed 1992/04/08, granted 1994/05/03
assignee Ricoh
[arithmetic coding]

5,311,177
Code transmitting apparatus with limited carry propagation
filed 1992/06/19, granted 1994/05/10
assignee Mitsubishi
[arithmetic coding]

5,347,600 (continuation of 5,065,447)
Method and apparatus for compression and decompression of digital image
filed 10/23/1991, granted 09/13/1994
inventors Barnsley and Sloan

5,363,099
Method and apparatus for entropy coding
[arithmetic coding with state machine]

5,384,867 (continued in 5,430,812)
filed 10/23/1991, granted 01/24/1995
Fractal transform compression board
inventors Barnsley et al.

5,404,140
Coding system
filed 1994/01/13, granted 1995/04/04
assignee Mitsubishi
[binary arithmetic coding, see also 5,307,062]

5,406,282
Data coding and decoding with improved efficiency
assignee Ricoh
[PPM & arithmedic coding]

5,414,423
Stabilization of probability estimates by conditioning on prior decisions
of a given context
assignee IBM
arithmetic coding]

5,416,856
Method of encoding a digital image using iterated image transformations
to form an eventually contractive map
filed 1992/03/30, granted 1995/05/16
inventors Jacobs, Boss and Fisher

5,418,532
Method and system for efficient, multiplication-free arithmetic coding
filed 1993/05/13, granted 1995/05/23.
inventors Lei & Shaw-Min
assignee Bell Communications Research, Inc. (Livingston, NJ).

5,430,812 (continuation of 5,384,867)
Fractal transform compression board
filed 1994/05/18, granted 1995/07/04
inventors Barnsley et al.

5,455,577
Method and system for data compression
filed 1993/03/12, granted 1995/10/03
inventors Slivka & Rashid, assignee Microsoft
LZ77 with two-level search data structure

5,533,051
Method for Data Compression
filed 1993/03/12, granted 1996/07/02
inventor David C. James, assignee The James Group
This is a patent on compression of random data, see item 9.5 below.

Japan 2-46275
Coding system
granted Feb 26, 1990
[Patents one form of arithmetic coding.]


--------------------------------------------------------------------------------

Subject: [9] Compression of random data (WEB, Gilbert and others)


[Note from the FAQ maintainer: this topic has generated and is still generating
the greatest volume of news in the history of comp.compression. Read this
before posting on this subject.

I intended to remove the WEB story from the FAQ, but similar affairs come up
regularly on comp.compression. The advertized revolutionary methods have all
in common their supposed ability to compress random or already compressed data.
I will keep this item in the FAQ to encourage people to take such claims with
great precautions.]


9.1 Introduction

It is mathematically impossible to create a program compressing without loss
*all* files by at least one bit (see below and also item 73 in part 2 of this
FAQ). Yet from time to time some people claim to have invented a new algorithm
for doing so. Such algorithms are claimed to compress random data and to be
applicable recursively, that is, applying the compressor to the compressed
output of the previous run, possibly multiple times. Fantastic compression
ratios of over 100:1 on random data are claimed to be actually obtained.

Such claims inevitably generate a lot of activity on comp.compression, which
can last for several months. Large bursts of activity were generated by WEB
Technologies and by Jules Gilbert. Premier Research Corporation (with a
compressor called MINC) made only a brief appearance but came back later with a
Web page at http://www.pacminc.com. The Hyper Space method invented by David
C. James is another contender with a patent obtained in July 96. Another large
burst occured in Dec 97 and Jan 98: Matthew Burch <apoc (AT) pipeline.com> applied
for a patent in Dec 97, but publicly admitted a few days later that his method
was flawed; he then posted several dozen messages in a few days about another
magic method based on primes, and again ended up admitting that his new method
was flawed. (Usually people disappear from comp.compression and appear again 6
months or a year later, rather than admitting their error.)

Other people have also claimed incredible compression ratios, but the programs
(OWS, WIC) were quickly shown to be fake (not compressing at all). This topic
is covered in item 10 of this FAQ.


9.2 The counting argument

[This section should probably be called "The counting theorem" because some
people think that "argument" implies that it is only an hypothesis, not a
proven mathematical fact. The "counting argument" is actually the proof of the
theorem.]

The WEB compressor (see details in section 9.3 below) was claimed to compress
without loss *all* files of greater than 64KB in size to about 1/16th their
original length. A very simple counting argument shows that this is impossible,
regardless of the compression method. It is even impossible to guarantee
lossless compression of all files by at least one bit. (Many other proofs have
been posted on comp.compression, please do not post yet another one.)

Theorem:
No program can compress without loss *all* files of size >= N bits, for
any given integer N >= 0.

Proof:
Assume that the program can compress without loss all files of size >= N
bits. Compress with this program all the 2^N files which have exactly N
bits. All compressed files have at most N-1 bits, so there are at most
(2^N)-1 different compressed files [2^(N-1) files of size N-1, 2^(N-2) of
size N-2, and so on, down to 1 file of size 0]. So at least two different
input files must compress to the same output file. Hence the compression
program cannot be lossless.

The proof is called the "counting argument". It uses the so-called pigeon-hole
principle: you can't put 16 pigeons into 15 holes without using one of the
holes twice.

Much stronger results about the number of incompressible files can be obtained,
but the proofs are a little more complex. (The MINC page http://www.pacminc.com
uses one file of strictly negative size to obtain 2^N instead of (2^N)-1
distinct files of size <= N-1 .)

This argument applies of course to WEB's case (take N = 64K*8 bits). Note that
no assumption is made about the compression algorithm. The proof applies to
*any* algorithm, including those using an external dictionary, or repeated
application of another algorithm, or combination of different algorithms, or
representation of the data as formulas, etc... All schemes are subject to the
counting argument. There is no need to use information theory to provide a
proof, just very basic mathematics. [People interested in more elaborate proofs
can consult http://wwwvms.utexas.edu/~cbloom/news/nomagic.html ]

In short, the counting argument says that if a lossless compression program
compresses some files, it must expand others, *regardless* of the compression
method, because otherwise there are simply not enough bits to enumerate all
possible output files. Despite the extreme simplicity of this theorem and its
proof, some people still fail to grasp it and waste a lot of time trying to
find a counter-example.

This assumes of course that the information available to the decompressor is
only the bit sequence of the compressed data. If external information such as a
file name, a number of iterations, or a bit length is necessary to decompress
the data, the bits necessary to provide the extra information must be included
in the bit count of the compressed data. Otherwise, it would be sufficient to
consider any input data as a number, use this as the file name, iteration count
or bit length, and pretend that the compressed size is zero. For an example of
storing information in the file name, see the program lmfjyh in the 1993
International Obfuscated C Code Contest, available on all comp.sources.misc
archives (Volume 39, Issue 104).

A common flaw in the algorithms claimed to compress all files is to assume that
arbitrary bit strings can be sent to the decompressor without actually
transmitting their bit length. If the decompressor needs such bit lengths
to decode the data (when the bit strings do not form a prefix code), the
number of bits needed to encode those lengths must be taken into account
in the total size of the compressed data.

Another common (but still incorrect) argument is to assume that for any file,
some still to be discovered algorithm might find a seed for a pseudo-random
number generator which would actually generate the whole sequence of bytes
contained in the file. However this idea still fails to take into account the
counting argument. For example, if the seed is limited to 64 bits, this
algorithm can generate at most 2^64 different files, and thus is unable to
compress *all* files longer than 8 bytes. For more details about this
"magic function theory", see http://www.dogma.net/markn/FAQ.html#Q19

Yet another popular idea is to split the input bit stream into a sequence of
large numbers, and factorize those numbers. Unfortunately, the number of bits
required to encode the factors and their exponents is on average not smaller
than the number of bits of the original bit stream, so this scheme too cannot
compress all data. Another idea also related to primes is to encode each
number as an index into a table of primes and an offset relative to the indexed
prime; this idea doesn't work either because the number of bits required to
encode the index, the offset and the separation between index and offset
is on average not smaller than the number of bits of the original bit stream.

Steve Tate <srt (AT) cs.unt.edu> suggests a good challenge for programs
that are claimed to compress any data by a significant amount:

Here's a wager for you: First, send me the DEcompression algorithm. Then I
will send you a file of whatever size you want, but at least 100k. If you
can send me back a compressed version that is even 20% shorter (80k if the
input is 100k) I'll send you $100. Of course, the file must be able to be
decompressed with the program you previously sent me, and must match
exactly my original file. Now what are you going to provide
when... er... if you can't demonstrate your compression in such a way?

So far no one has accepted this challenge (for good reasons).

Mike Goldman <whig (AT) by.net> makes another offer:

I will attach a prize of $5,000 to anyone who successfully meets this
challenge. First, the contestant will tell me HOW LONG of a data file to
generate. Second, I will generate the data file, and send it to the
contestant. Last, the contestant will send me a decompressor and a
compressed file, which will together total in size less than the original
data file, and which will be able to restore the compressed file to the
original state.

With this offer, you can tune your algorithm to my data. You tell me the
parameters of size in advance. All I get to do is arrange the bits within
my file according to the dictates of my whim. As a processing fee, I will
require an advance deposit of $100 from any contestant. This deposit is
100% refundable if you meet the challenge.


9.3 The WEB 16:1 compressor

9.3.1 What the press says

April 20, 1992 Byte Week Vol 4. No. 25:

"In an announcement that has generated high interest - and more than a
bit of skepticism - WEB Technologies (Smyrna, GA) says it has
developed a utility that will compress files of greater than 64KB in
size to about 1/16th their original length. Furthermore, WEB says its
DataFiles/16 program can shrink files it has already compressed."
[...]
"A week after our preliminary test, WEB showed us the program successfully
compressing a file without losing any data. But we have not been able
to test this latest beta release ourselves."
[...]
"WEB, in fact, says that virtually any amount of data can be squeezed
to under 1024 bytes by using DataFiles/16 to compress its own output
multiple times."

June 1992 Byte, Vol 17 No 6:

[...] According to Earl Bradley, WEB Technologies' vice president of
sales and marketing, the compression algorithm used by DataFiles/16
is not subject to the laws of information theory. [...]
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

9.3.2 First details, by John Wallace <buckeye (AT) spf.trw.com>

I called WEB at (404)514-8000 and they sent me some product
literature as well as chatting for a few minutes with me on the phone.
Their product is called DataFiles/16, and their claims for it are
roughly those heard on the net.

According to their flier:

"DataFiles/16 will compress all types of binary files to approximately
one-sixteenth of their original size ... regardless of the type of
file (word processing document, spreadsheet file, image file,
executable file, etc.), NO DATA WILL BE LOST by DataFiles/16."
(Their capitalizations; 16:1 compression only promised for files >64K
bytes in length.)

"Performed on a 386/25 machine, the program can complete a
compression/decompression cycle on one megabyte of data in less than
thirty seconds"

"The compressed output file created by DataFiles/16 can be used as the
input file to subsequent executions of the program. This feature of
the utility is known as recursive or iterative compression, and will
enable you to compress your data files to a tiny fraction of the
original size. In fact, virtually any amount of computer data can
be compressed to under 1024 bytes using DataFiles/16 to compress its
own output files muliple times. Then, by repeating in reverse the
steps taken to perform the recusive compression, all original data
can be decompressed to its original form without the loss of a single
bit."

Their flier also claims:

"Constant levels of compression across ALL TYPES of FILES"
"Convenient, single floppy DATA TRANSPORTATION"

From my telephone conversation, I was assured that this is an
actual compression program. Decompression is done by using only the
data in the compressed file; there are no hidden or extra files.


9.3.3 More information, by Rafael Ramirez <rafael.ramirez (AT) channel1.com>:

Today (Tuesday, 28th) I got a call from Earl Bradley of Web
who now says that they have put off releasing a software version of
the algorithm because they are close to signing a major contract with
a big company to put the algorithm in silicon. He said he could not
name the company due to non-disclosure agreements, but that they had
run extensive independent tests of their own and verified that the
algorithm works. [...]

He said the algorithm is so simple that he doesn't want anybody
getting their hands on it and copying it even though he said they
have filed a patent on it. [...] Mr. Bradley said the silicon version
would hold up much better to patent enforcement and be harder to copy.

He claimed that the algorithm takes up about 4K of code, uses only
integer math, and the current software implementation only uses a 65K
buffer. He said the silicon version would likely use a parallel
version and work in real-time. [...]


9.3.4 No software version

Appeared on BIX, reposted by Bruce Hoult <Bruce.Hoult (AT) actrix.gen.nz>:

tojerry/chaos #673, from abailey, 562 chars, Tue Jun 16 20:40:34 1992
Comment(s).
----------
TITLE: WEB Technology
I promised everyone a report when I finally got the poop on WEB's
16:1 data compression. After talking back and forth for a year
and being put off for the past month by un-returned phone calls,
I finally got hold of Marc Spindler who is their sales manager.

_No_ software product is forth coming, period!

He began talking about hardware they are designing for delivery
at the end of the year. [...]


9.3.5 Product cancelled

Posted by John Toebes <toebes (AT) bnr.ca> on Aug 10th, 1992:

[Long story omitted, confirming the reports made above about the
original WEB claims.]

10JUL92 - Called to Check Status. Was told that testing had uncovered a
new problem where 'four numbers in a matrix were the same
value' and that the programmers were off attempting to code a
preprocessor to eliminate this rare case. I indicated that he
had told me this story before. He told me that the
programmers were still working on the problem.

31JUL92 - Final Call to Check Status. Called Earl in the morning and
was told that he still had not heard from the programmers. [...]
Stated that if they could not resolve the problem then there would
probably not be a product.

03AUG92 - Final Call. Earl claims that the programmers are unable to
resolve the problem. I asked if this meant that there would
not be a product as a result and he said yes.


9.3.6 Byte's final report

Extract from the Nov. 95 issue of Byte, page 42:

Not suprisingly, the beta version of DataFiles/16 that reporter Russ Schnapp
tested didn't work. DataFiles/16 compressed files, but when decompressed, those
files bore no resemblance to their originals. WEB said it would send us a
version of the program that worked, but we never received it.

When we attempted to follow up on the story about three months later, the
company's phone had been disconnected. Attempts to reach company officers
were also unsuccessful. [...]


9.4 Jules Gilbert

As opposed to WEB Technologies, Jules Gilbert <jules (AT) aasp.net> does not
claim to compress *all* files, but only "random or random-appearing" files.
Here are some quotes from a few of Mr Gilbert's articles, which can be helpful
to get a better idea of his claims. No comments or conclusions are given; if
you need more information contact Mr. Gilbert directly.

From: coffee (AT) spock.ici.net (Jules Gilbert)
Newsgroups: comp.compression
Subject: Re: No Magic Compressors, No Factoring Compressors, Jules Gilbert
is a liar
Date: 14 May 1996 03:13:31 -0400
Message-ID: <4n9bqr$89k (AT) spock.ici.net>

[...]
I will, in front of several Boston area computer scientists ('monitors'),
people I choose but generally known to be fair and competent, under
conditions which are sufficient to prevent disclosure of the method and fully
protect the algorithm and other aspects of the underlying method from
untoward discovery, use two computers, (which I am permitted to examine but
not alter) with both machine's running Linux, and with the file-systems and
Linux OS freshly restored from commercial CD-ROM's do the following:

On one machine (the '