🚀 go-pugleaf

In article <Bts2CG.MM0@watdragon.uwaterloo.ca> kcwellsc@watdragon.uwaterloo.ca (Ken Wellsch) writes:
>> An ST-225 is RD31 and *is* standard.  Make sure that it selects on DS0. 
>> You'll know you're right because it will light up when selected.
>
>The only point I would like to make about determining whether drive RDxx
>works okay is this:  my experience with Pro's and RD drives is that if
>the drive meets or exceeds the required # hds/cyls etc. it may appear
>to be working fine but you may well not be using more than say the drive
>it thinks it is.  Example, if an RD51 is not jumpered correctly, a Pro
>(with Venix) will happily think the drive is an RD50 (5Mb rather than
>10Mb).  So please if you find something works, check how much space you
>*really* have available, it may not be the actual drive's capacity at all.

I have heard some of this before, all too fuzzy though.

I have seen actual DEC RD51 drives that come with metallic cutable jumpers on 
the DS lines.  DS0, DS1, DS2 are intact and DS3 is cut.  This means that this
particular drive will select on 0 or 1 or 2 but not 3.  I have been told that
the reason for cutting the DS3 line is that in (presumably one of the PRO
models, because it ain't a DECmate or RB), the controller uses the incompatible
notion of *reading* back DS3 instead of potentially asserting it.  Thus, a
5 Meg has the DS3 set and a 10 Meg has it clear, so the machine "knows" what
size disk it is.  (This is back when there only were RD50 and RD51 supported.)

Is there anything to this?

cjl