  
PSS ID Number: Q95533
Article last modified on 01-03-1996
PSS database name: MSDOS
 
6.00 6.20 6.21 6.22 | 95
 
MS-DOS              | WINDOWS

Largest possible DoubleSpace/DriveSpace Drive is 512MB
 

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The information in this article applies to:
 
 - Microsoft MS-DOS operating system versions 6.0, 6.2, 6.21, 6.22
 - Microsoft Windows 95
 - Microsoft Plus! for Windows 95
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SUMMARY
=======
 
The versions of DoubleSpace and DriveSpace included with MS-DOS and Windows
95 support cluster sizes up to 8K. This limits the size of a DoubleSpace or
DriveSpace compressed volume file (CVF) to 512 MB.
 
Because DriveSpace 3 (the version of DriveSpace included with Microsoft
Plus!) can use cluster sizes up to 32K, the maximum size for a DriveSpace 3
CVF is 2 GB.
 
MORE INFORMATION
================
 
The following calculations are used to determine the limits stated above:
 
DoubleSpace and DriveSpace
--------------------------
 
   # of clusters with FAT16      max cluster size      max CVF size
   ------------------------  *  ------------------  =  ------------
        65536 clusters          8192 bytes/cluster        512 MB
 
DriveSpace 3
------------
 
   # of clusters with FAT16      max cluster size       max CVF size
   ------------------------  *  -------------------  =  ------------
        65536 clusters          32768 bytes/cluster        2 GB
 
DriveSpace 3 achieves a higher compression ratio by compressing and storing
data in clusters up to 32K in size, and by offering two new levels of
compression called HiPack and UltraPack. For information about the HiPack
and UltraPack compression methods, search for "HiPack" and "UltraPack" in
DriveSpace 3 online Help.
 
DriveSpace 3 can also store more data than earlier versions of DriveSpace
and DoubleSpace because of improved fragmentation handling. In DoubleSpace
and DriveSpace CVFs, the data for a cluster must be stored in contiguous
sectors. When the volume is highly fragmented, it is possible to have many
free sectors, but not enough contiguous sectors to store a cluster (up to
16 sectors in a DoubleSpace or DriveSpace CVF, and up to 64 sectors in a
DriveSpace 3 CVF). DriveSpace 3 stores data for a fragmented cluster in a
linked list of sectors when there are not enough continuous sectors to
store the entire cluster. In addition, DriveSpace 3 stores small
directories in a single sector, while DoubleSpace and DriveSpace require 16
sectors.
 
All versions of DoubleSpace and DriveSpace use Sector Allocation
Granularity to increase data storage capacity. For additional information
about this topic, please see the following article in the Microsoft
Knowledge Base:
 
   ARTICLE-ID: Q98407
   TITLE     : How DoubleSpace Uses Sector Allocation
 
For information about cluster sizes, please see the following article in
the Microsoft Knowledge Base:
 
   ARTICLE-ID: Q67321
   TITLE     : FAT Type and Cluster Size Depends on Logical Drive Size
 
For information about DoubleSpace and DriveSpace in MS-DOS, please see
Chapter 5 of the "Microsoft MS-DOS 6 User's Guide," or see Appendix E of
the "Microsoft MS-DOS 6.22 User's Guide."
 
KBCategory: kbenv kbtool
KBSubcategory: win95 msdos winplus dblspace drvspace
Additional reference words: 95 6.00 6.20 6.21 6.22
=============================================================================
Copyright Microsoft Corporation 1996.


 
