TBBS 2.2 - Disk Compression Software

Contact:   eSoft, Inc. (Makers of TBBS)
           15200 E. Girard Ave., Suite 3000
           Aurora, CO  80014
           (303) 699-6565      Voice
           (303) 699-6872      Fax
           (303) 699-8222      BBS
           support@esoft.com   E-Mail

DISK COMPRESSION SOFTWARE
-------------------------

INTRODUCTION

Although the cost per megabyte for hard disk space has dropped in recent 
years, the demand for ever-greater disk capacity continues to rise.  In an 
effort to address this demand, many users turn to disk compression 
software such as "Stacker" from Stac Electronics.  In addition, Digital 
Research's DR-DOS as well as MS-DOS 6.0 feature basic disk compression 
options.  

DISK compression is different from FILE compression.  File compression, 
performed by programs such as ZIP, ARC, LHARC, ARJ, etc., is used "on
demand" to compress a specific set of files into a single, separate file.  
Disk compression, such as Stacker, Double Disk, etc., is used to compress 
ALL files on your hard disk "on the fly" automatically to increase the net 
amount of disk space available.

Disk compression software installs as a resident program (TSR).  They work 
by intercepting all disk I/O calls from programs that are running (like 
TBBS).  When a file is written to disk, the disk compressor uses 
compression algorithms to "squeeze" the data in the file.  When a file is 
read from the disk, the compressor steps in to "unsqueeze" the file back 
to its original state.  Disk compression software performs these 
operations automatically and transparently, and in a mode that is 
compatible with any program that uses DOS calls for its disk I/O.  The 
result is that a disk can hold more data than is otherwise possible, 
because the data stored there is compressed.  

Manufacturers of disk compression software claim up to a 100% increase 
(double) in storage capacity.  In reality, the exact increase is dependent 
on the types of data you store on your hard disk.  

QUESTIONS AND ANSWERS ABOUT DISK COMPRESSION AND TBBS


Q.  Is TBBS compatible with disk compression software?

A.  Yes -- with an explanation.

TBBS uses DOS I/O calls for all its disk I/O, and is therefore technically 
compatible with disk compression software.  In other words, TBBS can co-
exist successfully with disk compression software.

It is important to understand that the performance of your disk system is 
CRITICALLY IMPORTANT to TBBS' successful and efficient operation.  In 
fact, in most cases, disk performance is MORE IMPORTANT than the speed of 
the computer on which you run TBBS!  ANY resident software which stands in 
between TBBS and the disk provides an opportunity to interfere with TBBS 
and affect its performance.  Disk compression software is no exception.

Because of the way disk compression works, disk performance may actually 
increase when READING data FROM the disk.  However, when WRITING data TO 
the disk, performance may suffer.  Whether it suffers, and to what degree 
it suffers, is dependent on the speed of your PC, the loading of TBBS, how 
many lines you run, and other factors.  If your system is already heavily 
loading your hard disk, disk compression software may negatively affect 
TBBS' overall performance.  In most cases, the additional loading caused 
by the disk compression software (if any) will not be detectable.  The 
only way to tell is "try it and see."  Keep good back-ups in case it 
becomes necessary to un-install the disk compression software later.


Q.  Can I use disk compression to double the available space in my file 
areas?

A.  Not really.  Disk compression effectiveness is totally dependent on 
the source data.  Most BBS file areas consist of files that have already 
been compressed with file compression software such as ARC, ZIP, LHARC, 
etc.  Such files will not be compressed much (if at all) by disk 
compression software.  The net result will be little or no additional disk 
space for your file areas.


Q.  Can disk compression do anything for TBBS then?

A.  Do some degree, yes.  Your message base files will compress nicely, as 
will any text-based information you keep online.  You may wish to adjust 
your installation of the disk compression software so that files areas are 
on non-compressed drives, while everything else is on a compressed drive.


Q.  I'm running a disk cache.  Is this compatible with disk compression? 

A.  It's risky.  Most disk compression software vendors recommend NOT 
caching compressed drives.  The reason is that if there is some sort of 
cache failure, data recovery on a compressed drive is substantially more 
difficult than an non-compressed drive -- if it's not impossible.  Disable 
disk caching on compressed drives, or follow whatever special instructions 
your disk compression software recommends for disk caching.  


- END -
TBBS0004
Rev. 10/93

Copyright (C) 1994 eSoft, Inc., All Rights Reserved.  Permission granted
to distribute this file in its entirety, without modification, to any
interested party.  Any other use requires the written permission of
eSoft, Inc.

IMPORTANT:  The information herein is subject to change without notice.
Please call or write to confirm factual information of importance to you
or your organization.

