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:
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
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
For more information on ECR:
• Run DoubleSpace, choose Change Ratio from the Drive menu, and then
press the F1 function key.
• 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:
To view the ACR for the DOS directory, type the following at the
MS-DOS command prompt:
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
where "n.n" 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.