Abstract of INFO-MAC archived Text file
   'cmp/driver-level-compression.txt'
  Uploaded 05/16/1993   17466 bytes

Date: Sun, 16 May 1993 14:00:10 -0500 
From: tonyh@msc.cornell.edu (Tony Huang)
Subject: [*] Review of eDisk and TimesTwo 

This is a review of the only two driver-level compression programs
currently available. It also addresses a number of other compression
related issues. I'll update this document when new information or new
product in this category (such as Stacker for Macintosh) becomes available.
I welcome any comment or suggestion, and espeicially your experience with
these products.

To the Moderators: please replace the file times-two.txt that I previous
submitted with this one.

Tony Huang
tonyh@msc.cornell.edu
Review of eDisk and TimesTwo
----------------------------

A little more than six months ago, Golden Triangle introduced TimesTwo, the
first driver-level compression program for the Mac. It remained the only
product of its kind until now. After a two-month delay, Alysis is finally
shipping eDisk (To be fair, TimesTwo was delayed for over three months
after the initial announcement). Despite the distinction of being the only
two driver-level compression programs currently on the market, the two
programs are quite different in a number of respects. The following is a
review of these two programs (Comparisons with other file-level compression
programs are also made where appropriate).

I. Driver-level Compression vs. File-level Compression

File-level compression programs for the Mac have been around for a while.
They compress (and decompress) data on a file-by-file basis. They basically
fall into two categories. In the first category are programs like StuffIt
and DiskDoubler.  With these programs, the user has to decide which file
(or files) to compress and initiate the action. In the second category are
programs that compress and decompress files automatically in the
background. Programs such as AutoDoubler, More Disk Space, SpaceSaver
belong to this second category. To operate in the background, these
programs typically require the installation of a control panel in your
System folder (More Disk Space patches the System file directly by
installing its own resources). Because of this requirement compatibility is
a problem. There is always the potential of conflict with another INIT
(also known as system Extension or Startup document) or control panel with
INIT code, or with the way a particular application works. These conflicts
may or may not be the fault of file-level compression but the potential is
there and is unavoidable at the file level. Another problem with file-level
compression is the lack of total transparency while moving files from disk
to disk (especially across a network).

Driver-level compression solves all these problems, theoretically. Since