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                              DriveSpace Tips
 
This topic provides tips for getting the most out of DriveSpace, and also
answers some common questions about DriveSpace. For additional information
about DriveSpace, see "Freeing Space by Using DriveSpace" in the Microsoft
MS-DOS User's Guide or the Microsoft MS-DOS User's Guide Addendum, or see
the <DRVSPACE> command.
 
What does DriveSpace do?
 
DriveSpace is a disk-compression program. It stores more files in less space
by storing those files more efficiently. Most files are stored fairly
inefficiently ── somewhat like a sponge that has a lot of air holes in it.
When you squeeze a sponge, it becomes temporarily smaller; but when you let
go of it, the sponge returns to its original shape and size. When you
compress a drive, DriveSpace "squeezes" the files on that drive until they
are as small as possible ── just like squeezing a sponge. A file stored on a
compressed drive stays "squeezed" until you use it. When the file is loaded
into memory, DriveSpace uncompresses the file so that it returns to its
original size, just as a sponge does when you let go of it. When you're
finished using the file, DriveSpace "squeezes" it again and stores it back
on the compressed drive.
 
When should I use DriveSpace?
 
You should use DriveSpace if you are running low on disk space and don't
want to invest in a larger hard disk drive. DriveSpace can dramatically
increase your available disk space. However, because DriveSpace uses at
least 33K of memory, it makes sense not to install DriveSpace unless you
need it.
 
How does DriveSpace "squeeze" a file?
 
Most files contain a lot of repeated data. When DriveSpace finds repeated
data in a file, it retains the first occurrence of that data, and replaces
any other occurrences of that data with a cross-reference to the first
occurrence. The cross-reference takes less space than the original data.
 
For example, the following phrase includes the repeated data "at ":
 
    The fat cat sat up.
 
DriveSpace compresses this sentence by replacing the repeated "at "
characters (including the space) with a cross-reference to the first "at ".
In this example, cross- references are represented by the # character:
 
    The fat c#s#up.
 
Why does DriveSpace compress some files more than others?
 
Some files contain more repeated data than others. For example, program
files are usually compiled so that they are stored as efficiently as
possible; program files are typically not as compressible as some other
types of files. Bitmap files and text files typically compress well, since
most such files contain a lot of repeated data. Files that were compressed
by using a standalone compression program such as PKZIP usually do not
compress any further; although you can store such files on a compressed
drive, there is little advantage to doing so.
 
Will DriveSpace slow down my system?
 
If you have a computer with a fast CPU and a fast hard disk, you probably
won't notice much difference in system speed after installing DriveSpace. If
you have a fast CPU and a slow hard disk, DriveSpace might actually improve
your system's speed. If your computer has a slow CPU, you may notice a
reduction in speed after compressing your drive.
 
What happens during DriveSpace Setup?
 
DriveSpace Setup configures your computer to run DriveSpace and compresses
the drive of your choice. DriveSpace Setup first runs ScanDisk to check your
hard disk for logical and physical errors. If necessary, it runs the
Microsoft Defragmenter to defragment the files on your disk. Finally, it
compresses the files on your drive. For more information about running
DriveSpace Setup, see "Freeing Space by Using DriveSpace" in the MS-DOS
User's Guide or the MS-DOS User's Guide Addendum.
 
Now that I've installed DriveSpace, why do I have an additional drive?
 
When DriveSpace Setup is complete, you will have an additional drive.
 
If you chose to create a new compressed drive, the additional drive is the
compressed drive you just created.
 
If you compressed an existing drive (for example, drive C) the additional
drive is an uncompressed drive. It is used to store files that must remain
uncompressed (such as the Windows swap file). The additional drive also
contains important system files such as IO.SYS, MSDOS.SYS, DRVSPACE.BIN,
DRVSPACE.INI and DRVSPACE.000.
 
CAUTION:  Do not delete or otherwise tamper with the hidden files on the new
          drive. If you do, you might lose your compressed drive and all the
          files it contains.
 
For more information about DriveSpace Setup, see the "Understanding Disk
Compression" section of "Freeing Space by Using DriveSpace" in the MS-DOS
User's Guide or the MS-DOS User's Guide Addendum,
 
Can I copy a file from a compressed drive to an uncompressed drive (such as
a floppy disk or a network drive)?
 
Yes. You can copy files between compressed drives and uncompressed drives
just as you would between two uncompressed drives. A file is actually
compressed only when it is stored on a compressed drive. When you copy a
file from your compressed drive, DriveSpace reads the file into memory and
uncompresses it. The file is then copied to the uncompressed drive in its
uncompressed state.
 
If I compress a drive and then add more files to it, do I need to recompress
the drive?
 
No. Whenever you copy a file to a DriveSpace drive, DriveSpace saves the
file in compressed form. It doesn't matter whether the file was on the drive
when you compressed the drive.
 
If I'm using DriveSpace, what should I do to maintain my system?
 
In general, maintaining a computer that's running DriveSpace is just like
maintaining an uncompressed system. To ensure the safety of your data and
the stability of your system, do the following frequently (for example, once
a week):
 
♦  Back up your data files regularly. You can back up your files by using
   either Backup for MS-DOS or Backup for Windows. For more information, see
   the following section. Also, see the chapter "Managing Your System" in
   the MS-DOS User's Guide.
 
♦  Check your hard disk regularly for logical and physical errors. To check
   and repair a drive, use the ScanDisk program. For more information, see
   <SCANDISK>.
 
♦  Check your computer's memory and hard disk for viruses. Viruses can
   damage data, and can even prevent your computer from starting or running
   properly. To check for viruses, use Anti-Virus. Be sure to check all your
   drives ── compressed and uncompressed drives. For more information, see
   the chapter "Managing Your System" in the MS-DOS User's Guide.
 
♦  Defragment your hard disk drive periodically. (Since defragmentation can
   take a long time, you might want to do it at the end of the day.) For
   more information, see the chapter "Managing Your System" in the MS-DOS
   User's Guide.
 
♦  Set up Undelete so that you can restore any files that you accidentally
   delete. For information about setting up Undelete, see the chapter
   "Managing Your System" in the MS-DOS User's Guide.
 
How should I back up my files if I'm using DriveSpace?
 
You should back up and restore the files on a compressed drive just as you
would the files on an uncompressed drive. (For information about using
Microsoft Backup, see the chapter "Managing Your System" in the MS-DOS
User's Guide.)
 
When backing up the files on the host drive (the uncompressed drive that
contains the compressed volume file (CVF) for your compressed drive), you
typically do not need to back up any files that have names in the form
DRVSPACE.nnn (for example, DRVSPACE.000). The DRVSPACE.nnn file essentially
contains your compressed drive. Although it is possible to back up the
DRVSPACE.nnn file, doing so is redundant if you have also backed up the
files on that compressed drive. In general, it's best to back up the files
on your compressed drive directly, rather than by backing up the associated
CVF (the DRVSPACE.nnn file). This is because backing up only the CVF does
not allow you to restore individual files or directories later. When you
restore the backup copy of a DRVSPACE.nnn file, it replaces the entire
compressed drive with the backup copy. This means that you will lose all
changes to all files on that drive that were made since the backup copy was
created.
 
I installed DriveSpace and now I'm running out of memory. What can I do?
 
If you have an 80386 or higher computer, run <MemMaker> after installing
DriveSpace. MemMaker can move portions of DriveSpace out of conventional
memory, which makes more memory available for running programs. Also, make
sure the BUFFERS command in your CONFIG.SYS file is set to no more than 10
buffers. For more information about BUFFERS and DriveSpace, see <BUFFERS>.
 
If you have an 80286 or higher computer with at least 1 MB of memory, make
sure your CONFIG.SYS file contains a DOS=HIGH command, a DEVICE command for
HIMEM.SYS and a DEVICE command for DRVSPACE.SYS. (MS-DOS Setup and
DriveSpace Setup normally add these commands to your CONFIG.SYS file.) With
these commands, MS-DOS and parts of DriveSpace can load into the high memory
area. (For information about loading DoubleSpace into the HMA, see
<DBLSPACE──Notes>.)
 
Is it all right to run SMARTDrive if I'm using DriveSpace?
 
SMARTDrive and DriveSpace are designed to work together. If Setup determines
that your computer has enough memory to run SMARTDrive, it automatically
installs SMARTDrive by adding a SMARTDRV command to your AUTOEXEC.BAT file.
In particular, you should run SMARTDrive if you are running DriveSpace and
you use Windows; in that case, using SMARTDrive can significantly speed up
your computer.
 
SMARTDrive is designed to speed up your system and safeguard your data. By
default, Setup configures SMARTDrive so that write-caching is disabled. (If
SMARTDrive was originally configured to allow write-caching, Setup will not
change your configuration.) Write-caching provides much faster performance
than read-only caching, but is not as conservative. For more information
about SMARTDrive, see <SMARTDRV>.
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