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     Microsoft Plus! Readme for DriveSpace and Compression Agent
                          August 1995            
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            (c) Copyright Microsoft Corporation, 1995


This document supplements the Microsoft Plus! documentation. It 
provides complementary or late-breaking information about DriveSpace 3 
disk compression and the Compression Agent file-compression program.

------------------------
HOW TO USE THIS DOCUMENT
------------------------

To view Drvspace.txt on screen in Notepad, maximize the Notepad window.

To print Drvspace.txt, open it in Notepad or another word processor,
and then use the Print command on the File menu.


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CONTENTS
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USING COPY-PROTECTED SOFTWARE WITH DRIVESPACE 3
FREEING CONVENTIONAL MEMORY FOR RUNNING MS-DOS PROGRAMS
USING DISK TOOLS WITH SIDEKICK FOR WINDOWS
COMPRESSION AGENT AND THE WINDOWS SWAP FILE
AUTOMOUNTING COMPRESSED FLOPPY DISKS
FREQUENTLY-ASKED QUESTIONS


COMPRESSING AND UPGRADING DRIVES
================================

Using Copy-Protected Software With DriveSpace 3
-----------------------------------------------

If you use copy-protected software, contact the manufacturer
before you compress or upgrade your drive using DriveSpace 3. 
Some copy-protected software depends on the absolute physical
location of a "key" file, and will not work properly with
DriveSpace 3.

You might be able to work around this problem by uninstalling 
the copy-protected software and then reinstalling it after 
compressing or upgrading your drive.


If a Drive Becomes Inaccessible After You Compress Another Drive
----------------------------------------------------------------

If, after compressing a drive, your CD-ROM drive or another hard 
disk drive becomes inaccessible or "disappears", the drive letter
may have been changed when DriveSpace reserved drive letters for 
other purposes.

To restore the original drive letter:

1. Use the right mouse button to click the My Computer icon on
   the desktop, and then click Properties.

2. Click the Device Manager tab.

3. Click the + sign to the left of the Disk Drives item, click
   the drive you want to restore, and then click Properties.

4. Set the drive letter back to the original drive letter for
   that drive.

If the original drive letter is not available, it is probably
in use by the host drive. (You can change the host drive to
use a different letter. To do this, run DriveSpace, select
the host drive, and choose Change Drive Letter from the 
Advanced menu.)


FREEING CONVENTIONAL MEMORY FOR RUNNING MS-DOS PROGRAMS
=======================================================

Some MS-DOS-based programs (for example, networks or games) may 
not be able to run if DriveSpace 3 compression is installed, even
if you have not yet upgraded your drives to DriveSpace 3 format. 
Typically, this problem occurs only when Windows is not running,
and with programs that require a lot of conventional memory.

To get your program to run, you need to reconfigure your
system so that more conventional memory is available. 

The general steps involved are:

1. Make sure your Config.sys file contains commands like the 
   following:

        DEVICE=C:\WINDOWS\HIMEM.SYS
        DEVICE=C:\WINDOWS\EMM386.EXE NOEMS
        DOS=HIGH,UMB
        DEVICEHIGH=C:\WINDOWS\COMMAND\DRVSPACE.SYS /MOVE

   These commands make it possible for DriveSpace to use
   upper memory, which can free more conventional memory for
   your program.

   NOTE: If the Devicehigh command for Drvspace.sys contains
         the /L:0 switch, delete the /L:0 from that command.

   If your Config.sys file does not contain these commands,
   add them. (To check whether DriveSpace is using upper 
   memory, type Mem /C at the MS-DOS prompt.)

2. Restart your system, and then try running your program again.

3. If your program still does not run, disable any unnecessary
   drivers and memory-resident programs in your Autoexec.bat
   and Config.sys files.

   Try loading device drivers by using the Devicehigh command 
   instead of the Device command. For example: 

        DEVICEHIGH=C:\WINDOWS\IFSHLP.SYS

   Try loading memory-resident programs by using the Loadhigh
   command. For example:

        LOADHIGH DOSKEY

   Restart your computer, and then try running your program again.

4. If your program still does not run, you need to create
   a startup floppy disk that you can use to start your computer
   without DriveSpace. You can then run your program from your
   uncompressed (host) drive. For more information, see the
   following section.


Creating a Startup Disk for Running MS-DOS Programs
---------------------------------------------------

If your MS-DOS program does not run because there is not enough free
conventional memory, and you have carried out the procedure in the
previous section, you may need to create a special startup floppy 
disk. You can then use that disk to start your computer without
DriveSpace, and then run your program from your uncompressed drive.

To create your startup disk, you will need the Startup Disk wizard,
nocomp.exe, which is located in the System subfolder of the folder
that contains your Microsoft Plus! files.

1. Make sure there is enough free space on your host drive (or 
   another uncompressed drive) to install your program. 

   To create more free space on your host drive, use the Adjust 
   Free Space command in DriveSpace. (For other ways to free space,
   look up "Disk space, freeing" in the Help index.)

2. Run the Startup Disk wizard to create your startup floppy disk.
   
   NOTE: You will need a formatted or unformatted floppy disk that 
         fits in drive A.

3. After the Startup Disk wizard finishes creating your startup
   floppy disk, insert the disk in drive A, and then restart 
   your computer.

   Your computer will start without loading DriveSpace. This will 
   free memory for your program to use. 
 
   NOTE:  Your compressed drives will be temporarily unavailable. 
          They will become available again when you restart your
          computer normally.

4. Install your program on your host drive or on another 
   uncompressed drive.


USING DISK TOOLS WITH SIDEKICK FOR WINDOWS
==========================================

If Sidekick for Windows version 2.0 is running, you may be unable to 
run certain disk tools, such as DriveSpace or Disk Defragmenter.

To work around this problem, first exit Sidekick, and then try 
running the disk tool again.

For an update to Sidekick that fixes this problem, contact the 
manufacturer.


COMPRESSION AGENT AND THE WINDOWS SWAP FILE
===========================================

When Compression Agent recompresses the files on your compressed
drive, it automatically skips the Win386.swp file. (This file,
known as the Windows swap file, provides virtual memory for 
Windows and applications to use.) There is no need to specifically
exclude the Win386.swp file from compression by using Compression
Agent's Exceptions dialog box.


AUTOMOUNTING COMPRESSED FLOPPY DISKS
====================================

DriveSpace 3 automatically mounts compressed floppy disks and
other removable media when Windows 95 is running.

However, when Windows is not running (for example, if you restart
your computer in MS-DOS mode), automounting is disabled. To
mount a compressed floppy disk yourself, you can use ScanDisk.
For example, to mount the compressed floppy disk in drive A, 
type the following at the command prompt:

    C:\> SCANDISK /MOUNT A:


FREQUENTLY-ASKED QUESTIONS
==========================

This section answers some common questions about how Windows
and DriveSpace report space usage on DriveSpace 3 drives.
 

Why do my files seem to take up more space on a DriveSpace 3 drive?
-------------------------------------------------------------------

The space on each drive is divided into units called clusters.
Each file or folder is stored in one or more clusters. When 
Windows stores a file on your drive, it allocates just enough 
clusters to hold the entire file. Because all the clusters on 
a particular drive are the same size, a portion of the last 
cluster for each file will probably be unused. For example, 
on a drive that uses 8K clusters, each file uses at least 
one 8K cluster, even if that file is only 1K in size. 

Windows keeps track of used space on a per-cluster basis:
when Windows reports how much space is used by a file, it 
includes the unused space at the end of the file's last 
cluster. For example, Windows would report that a 1K file
uses 8K of space.

Larger drives have larger cluster sizes. In order to support 
very large (2GB) drives, DriveSpace 3 uses 32K clusters.
This means that even a very small file still uses 32K of
space. As a result, when you view the properties for your 
drive, the amount of used space might appear to be higher 
than before you compressed the drive with DriveSpace 3.


Does this mean that more space is wasted on DriveSpace 3 drives?
----------------------------------------------------------------

No. On the contrary, DriveSpace 3 stores files much more 
efficiently than on an uncompressed drive. In addition 
to saving space by compressing the data in each file, 
DriveSpace 3 also saves space by allocating smaller amounts 
of physical disk space for each file. Although Windows 
still keeps track of files in units of clusters (which is 
why your files may appear to take up more space), DriveSpace 
actually uses 512-byte units when allocating physical space 
for each file. This means that no more than 512 bytes of 
actual disk space is wasted when allocating a file on a 
DriveSpace 3 drive.


What is "reduced overhead"?
---------------------------

When you view the properties for a compressed drive and 
click on the Compression tab, you'll typically see that some 
disk space was saved due to "reduced overhead." This 
is due to the fact that DriveSpace actually stores files in 
512-byte increments, rather than in larger clusters, as 
would happen on an uncompressed drive. Reduced overhead 
reflects the amount of space saved by using this more 
efficient allocation, relative to the amount of space that 
would have been required to store the same files on the 
same drive if it was uncompressed. Reduced overhead does 
NOT include the savings from the actual compression of your 
data.


What do the numbers on the Compression tab mean?
------------------------------------------------

The Compression tab of the property sheet for a drive 
shows how your files are being compressed and how much 
space each type of compression is saving. 

For each type of compression, the compression ratio is 
computed by dividing the amount of data stored in that type 
of compression by the amount of physical disk space actually 
used to store the data. For example, if you have 100MB of 
data stored in UltraPack format, and its compression ratio 
is 2.5 to 1, then DriveSpace 3 is storing that data using 
only 40MB of physical space on your hard disk. As a result, 
the Gain column indicates that you've saved 60MB of space by 
using UltraPack compression.  

The overall compression ratio for a drive is an average of 
all the compression types, plus the savings from Reduced 
Overhead. It represents the ratio between the amount of 
space that would have been required to store the same files on 
the same drive if it were not compressed, and the amount of 
physical disk space that DriveSpace is actually using to store 
those files.


Why isn't the compression ratio for UltraPack higher?
-----------------------------------------------------

UltraPack compression generally achieves the highest 
possible compression. However, because DriveSpace can read 
and write data stored in HiPack format more quickly than 
data stored in UltraPack, it uses HiPack format unless 
using UltraPack can save a significant amount of disk 
space. Because only the data that is most difficult to 
compress will be stored in UltraPack format, the ratio 
shown for UltraPack may actually be lower than that for HiPack.


Why are some files not compressed at all?
-----------------------------------------

On many drives, a significant amount of data will be listed 
as being uncompressed. There are several reasons that
particular files may not be compressed:

 * Files that are smaller than 512 bytes are never 
   compressed. (DriveSpace 3 compresses a file only 
   if it can save at least 512 bytes of disk space by 
   doing so.)

 * Space used on your drive to store folders is never 
   compressed.

 * The Windows swap file is never compressed. (This file
   provides virtual memory by using space on your hard 
   disk.)

 * Certain files may not be compressed if you have 
   configured Compression Agent to prevent it from 
   compressing those files.

 * Files that are already compressed, such as JPEG or ZIP 
   files, typically can't be compressed any further by 
   DriveSpace, so they are listed as uncompressed.  

 * Some files that do not compress well, such as program 
   files (.EXE and .DLL files), may have portions that do 
   not compress at all. These portions are listed as
   uncompressed.

