Compression function DAT 20/40

[Andreas_42]

I am a novice here, please help me with this question, thanks a lot.
How can a hp DAT 20/40 tape achieve its compressed capacity? I tried to changed the compressed-switch in the OS driver settings (Windows Server 2003) but all fields aren't rewriteable. The Hardware Switch 1 and to 2 (Comnpression enabled at power on, no host control) are also not functional. Can somebody help me ?

[Cameron Todd]

I thought that most tapes drives normally have on-board hardware compression switched on by default, regardless of the backup software on the host.

How well the compression works depends on what sort of files are being backed up. ZIP's and executables will not compress well so would estimate that actual capacity would not be much better than the raw figure, whereas text, document and (some) database files would compress well and the actual capacity of the tape would rise to closer to the theoretical maximum compressed capacity.

What sort of real results are you getting with your backups in terms of tape capacity?