On Fri, Oct 24, 2003 at 09:43:38AM +0100, Tony wrote:
> Hi,
> 
> Good idea. I have done this now. Went and downloaded the manual
> and there are two DIP switches that are relevant. I quote from
> the manual:
> 
> -------
> Data Compression (switches 1 and 2)
> 
> If switch 1 is ON (default), HW data compression is enabled. If
> switch 1 is OFF, HW data compression is disabled. 
> 
> If dip switch 2 is ON (default), then SCSI commands can be used
> to enable or disable HW data compression. To prevent HW data
> compression from being enabled or disabled by SCSI commands, set
> DIP switch 2 to OFF
> -------
> 
> That all sounds pretty straight forward. I turned dip switches 1
> & 2 OFF so that HW compression is disabled and can't be turned
> on again by the software.
> 
> I would hope that if I have physically set these switches, that
> even putting in a tape that was previously written on with
> compression enabled could not over-ride the DIP switch settings.
> 

I would not make that assumption.
The manual description of the effect of SW-2 refers to the ability
of software to change the compression setting, not the ability of
the hardware itself to change the setting.  Otherwise you would
not be able to 'read' tapes previously compressed.  Certainly
not a desireable trait.

I would 'expect', but not assume, that after switching to HW
compression ON during a read, subsequent writes would still be 
compression OFF if SW-2&1 and is off.  But one never knows does one?

BTW the manual for my drive has similar dip switch settings.  
SW-1 is refered to as the "power on state".  So the drive must
be power cycled to restore that state after a switch change.
SW-2 is described as enabling/disabling software control of
the compression state.  But it doesn't say the hardware can't
change the state.

-- 
Jon H. LaBadie                  jon AT jgcomp DOT com
 JG Computing
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