Dr. David Alan Gilbert (dg@px.uk.com)
Wed, 07 Apr 1999 13:47:52 +0100
marbud@tripnet.se wrote:
BE CAREFUL!
> I stumbled over two old DIGITAL SCSI hard disks (RF74-EA). The only
> information i can find about them is a price tag and the word DSCSI.
>
> I think DSCSI stands for Differential SCSI but searching for a
> suitable SCSI adapter i find cards supporting only low voltage
> differential (LVD) OR high voltage differential (HVD).
>
> Question 1: What is DSCSI! LVD or HVD?
On normal SCSI you have one wire per data signal and you also have a
ground signal.
On Differential SCSI there are two wires per data signal and the data is
measured
as the voltage difference of the two.
Differential SCSI has been around for a long time and provides for
longer
cable lengths and more reliability in really bad environments.
LVD is new - it uses lower voltages; but is still differential like
above -
it is used in the newest form of SCSI; Ultra-2 SCSI. You can have
longer
cable lenths and a higher speed.
Now the problem - you can NOT use an old Differential SCSI disc on a
normal
SCSI adapter - something will be DAMAGED (i.e. broken - i.e.
permenantly!).
I'm not sure about the LVD discs; but my underdstanding is that these
will
work with normal SCSI adapters safely - but it is definitly worth
checking first!
I'm not sure if the modern LVD controllers also support the old
Differential - I'm guessing
they dont.
> Question 2: Does differential (LVD or HVD) SCSI work with RedHat
> 5.2/Linux?
I see no reason why not.
> PS
> The SCSI connector on the disk looks just like the old ones (50
> pins..)
Yes - that is just to fool you - old differential discs have the same
connectors as normal non-differential ones. This just makes you think
that all is safe and well - before you plug it in and blow
one up.
Dave
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