From: costello@stx.UUCP (Michael E. Costello)
Newsgroups: comp.sys.mac.apps
Subject: Re: AutoDoubler vs. More Disk Space Questions
Date: Fri, 17 Apr 92 13:09:34 GMT
Organization: BCS*Mac
Reply-To: stx!costello@world.std.com
X-Mailer: uAccess - Macintosh Release: 1.5v3

Let me throw this into the hopper. I have included an elucidation of
various aspects of MDS supplied to my by the author of MDS. Speaking
for myself, I have not used either product, so I'm passing this along
as-is.


In article <1992Apr15.233337.6697@cserver.plexus.COM> (comp.sys.mac.apps), craigh@cserver.plexus.COM (Craig Heilman) writes:
|  >	I know there's been a discussion going on about compression
|  >utilities, and I've found it very informative.  I am interested
|  >in purchasing one of two utilites, either AutoDoubler (AD) or More Disk
|  >Space (MDS), and I have some specific questions about the!

>
> 1) Does AD or MDS change a file's type?
>

More Disk Space does not change type or creator.  This means that applications
which use the standard file dialog box to open files can still open those 
files and that programs like On Location still work properly.  More Disk Space
does compress After Dark Modules and other items in the system folder for 
significant space savings.  Anti-virus programs like SAM virus clinic will 
work properly on MDS compressed applications, even without the presence of the
MDS software.

>
> 2) Does AD or MDS check for file integrity after compression (checksum)?
>

More Disk Space adds a checksum whenever it compresses a document.  If the 
checksum fails when the document is being read, the user is presented with an 
alert allowing the user to continue the decompression operation at his own 
risk or cancel it to allow a graceful read failure.

>
> 3) Does AD or MDS delete a file before saving the compressed verstion?
>

More Disk Space never deletes a file until the entire compression operation is
complete.  David Pogue was not quite acurate in his description of SuperDisk! 
compression.  With SuperDisk!, users have the option of compressing with 
tempfiles or without.  Because of the criticism from the Salient/Pogue team, 
we decided to eliminate the option and make every compression operation use a 
tempfile.  This gives up substantial functionality, especially on large files,
but it does quiet the strident Salient bunch.

More Disk Space goes a step further to provide more safety still.  At the 
user's option, it will verify _all_ write operations.  This will prevent the 
loss of data to bad media in situations where other programs would give no 
warning.

And since More Disk Space operates from its own bootable floppy disk, on 
global compression operations, you can be sure that it will not spread a virus
from one program to the next as it operates.

>
> 4) Does AD or MDS change a file's icon after compression?
>

More Disk Space does not change or even compress icons.  It is possible to add
or edit custom icons to compressed files without decompressing them or even 
having More Disk Space installed.

>
> 5) MDS states that it uses some type of standard compression, and
   this means that a file can be decompressed without MDS being 
   present.  Is this true?  If so, how "standard" is this algorithm
   (ie are they using an algorithm Apple will support in future system
   releases)?
>

More Disk Space employs Apple's resource compression scheme to achieve gains 
in speed and compatibility over other compression methods.  The resource 
compression scheme is currently used by the System, the Finder, ResEdit and 
TeachText.  The difference is the algorithm.  The More Disk Space algorithm 
compresses tighter than Apple's.  ResEdit uncompressed (Something most people 
never see) is about 900K.  With Apple's compression it's about 650K.  With MDS
it's about 550K.   On the basic System 7 file, MDS gains about 160K over 
Apple's current method.

The resource compression mechanism is proven and frozen according to senior 
mac guru Chris DeRossi.  New decompression resources may be added for better 
performance, though.  That is how More Disk Space works.

The More Disk Space transportable compressed applications (TCAs) don't 
actually decompress on systems without More Disk Space;  they just execute in 
compressed form.  Since the vers, icl8, icl4, icn#, ics4, ics8 resources are 
not compressed, Get Info commands work properly,  locking and unlocking the 
TCAs works properly and TCAs which save preferences work properly.   You can 
even use ResEdit on a system without MDS to open and edit TCAs.

I'll be happy to answer any other questions about More Disk Space or resource 
comrpession.

Justin Gray,
Alysis Software Corporation (makes More Disk Space)

______________________________________________________________________________


Michael Costello, Executive Director * costello@world.std.com * 617-631-8188
     BCS*Mac  *  The Boston Computer Society Macintosh User Group
Newsgroups: comp.sys.mac.apps