Microsoft Plus! Drvspace.txt File Contents

The information in this article applies to:

• Microsoft Plus! for Windows 95

SUMMARY

The following information is a copy of the information in the Microsoft Plus! for Windows 95 Drvspace.txt file.

MORE INFORMATION

CONTENTS

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.

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.