Hardware compression takes place after the backup software has transfered
data to the tape device. Software compression is done by the backup software
before data is transfered. Back in the 286/386/486 days, most people prefered
to use hardware because of the extra overhead required to do the compression.
With PII processors and above, you should see no difference in throughput
between the two.

As far as not getting 24 Gb on a 12/24 drive, see http://seer.support.veritas.com/docs/199542.htm
"Ray Li" wrote:
>
>I am using HP DAT24e DAT tape recorder for data backup with Backup Exec
v7.3.
> In job definition, it has option of hardware or software compression.
What
>are the differencies between hardware and software compressions? Although
>I am using DAT24 tape but seems never achieved close to 24 GB, 12-13 GB
normally.
> Any suggested solutions?
>
>Thanks,
>
>Ray