Microsoft KB Archive/96391

= DoubleSpace Estimated & Actual Compression Ratios =

Article ID: 96391

Article Last Modified on 1/1/2001

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APPLIES TO


 * Microsoft MS-DOS 6.0 Standard Edition
 * Microsoft MS-DOS 6.2 Standard Edition
 * Microsoft MS-DOS 6.22 Standard Edition
 * Microsoft Windows 95

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This article was previously published under Q96391



SUMMARY
This information applies to both Microsoft DoubleSpace and Microsoft DriveSpace. For MS-DOS 6.22, use DRVSPACE in place of DBLSPACE for commands and filenames.

This article discusses common questions and issues with DoubleSpace actual compression ratio (ACR) and estimated compression ratio (ECR). The following three subjects are covered:


 * Actual Compression Ratio
 * Estimated Compression Ratio
 * Viewing and Changing the Compression Ratio



Actual Compression Ratio
The actual compression ratio (ACR) represents the compression ratio for data that already exists on a drive. The ACR varies over time depending on the type of files you store on your hard disk.

The ACR is calculated by dividing the sum of the uncompressed data size by the physical space consumed after the data is compressed. For example, if a disk with 100 megabytes (MB) of uncompressed data is compressed and occupies 50 MB of disk space, the compression ratio is 2:1. The formula is as follows:   100MB/50MB =2.0 NOTE: 2.0 is written as 2.0:1 (that is, 2 to 1)

Estimated Compression Ratio
The estimated compression ratio is a number that DoubleSpace uses to calculate the amount of free space on a compressed drive. Changing the ECR doesn't change the compression algorithm or the ACR. It simply changes the value that DoubleSpace uses to estimate the free disk space.

You may need to increase the compression ratio if you are trying to store several new highly compressible files and you are low on disk space.

For more information on ECR:


 * Run DoubleSpace, choose Change Ratio from the Drive menu, and then press the F1 function key. -or-


 * Type help dblspace /ratio at the MS-DOS command prompt.

Viewing and Changing the Compression Ratio
To view the ACR and ECR for a drive, type dblspace at the MS-DOS command prompt, select the drive you are interested in, and then press the ENTER key.

To view the ACR for a file or directory, use the DIR /C or DIR /CH command. For example, to see the ACR for COMMAND.COM, type the following at the MS-DOS command prompt:

dir c:\command.com /ch

To view the ACR for the DOS directory, type the following at the MS-DOS command prompt:

dir \dos /ch

NOTE: DIR /C reports the ACR of the compressed data based on an 8-kilobyte (K) cluster size. DIR /CH reports the ACR based on the compressed data based on the host drive cluster size. Use this number when you compare the ACR and ECR.

To set the ECR to the ACR value, type dblspace /ratio at the MS-DOS command prompt.

To set the ECR to a specific value, type the following at the MS-DOS command prompt:

dblspace /ratio=n.n

where &quot;n.n&quot; is the ECR value.

NOTE: Changing the size of the host drive changes the ECR from the default value (2.0:1) to the ACR value.

Additional query words: 6.00 double space dblspace 6.20

Keywords: KB96391

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