Path: utzoo!attcan!uunet!ogicse!uwm.edu!psuvax1!psuvm!trl3
From: TRL3@psuvm.psu.edu (Tim Larson)
Newsgroups: comp.sys.cbm
Subject: Re: LZW in 64K
Message-ID: <90061.123838TRL3@psuvm.psu.edu>
Date: 2 Mar 90 17:38:38 GMT
References: <12000.25e95ff6@cc.nu.oz>
Organization: Penn State University
Lines: 30

For those implementing the LZW algorithm: I quote from a letter in Dr. Dobbs
Journal, March 1990, page 8.  The author is Robert S. Bramson of Unisys, the
owner of U.S. Patent 4,558,302 entitled "High Speed Data Compression and
Decompression Apparatus and Method."  (That is, Unisys is the owner.)

"As a concession to the modem industry, Unisys has agreed to license the
patent to modem manufacturers for use in modems conforming to the V42.bis
data compression standard promulgated by CCITT, for a one-time fee of $20,000.
This $20,000 license, however, is not a general license under all applications
of our patent but is limited to the specific appication discussed above."

"...Unisys is actively looking into the possibility that a large number of
software developers may be infringing one or more of our data compression
patents."

"Unisys is happy to accept inquiries from persons interested in acquiring a
license to U.S. Patent 4,558,302.  ...contact Mr. Edmund Chung of [Unisys']
licensing office, at 313-972-7114."

This is pretty scary stuff.  Many PD and shareware data compression schemes
(including the GIF image standard) are based wholly or in part on LZW.  LZW
schemes are aften written about in books and taught in classes on data
compression.  Futhermore, LZW is simply one of many variations of a specific
family of data compression algorithms.  What kind of issues do this patent
and Unisys' recent interest in it raise?  That letter was enough for me to
yank LZW algorithms out of our software until I get the scoop from Unisys.

Cheers!
-Tim Larson
trl3@psuvm.bitnet