Date   : Thu, 12 Nov 2009 00:12:38 +0000
From   : afra@... (Phill Harvey-Smith)
Subject: Leicester RCM Show (RM Nimbuses)

Alex Taylor wrote:
> 2009/11/11 Phill Harvey-Smith <afra@...>:
> 
>> Looking at your disk controler board, it looks like it *may* be
>> capable of being upgraded to run a hard disk, by addition of some
>> extra chips.
> 
> I remember two of mine being floppy-only, and one having a hard-disk 
> capable card (without the hard disk, unfortunately, although the
> front panel boldy stated "20MB", with a little red window for the
> LED). The cards were the same, only the floppy-only ones were missing
> the appropriate chips.

Yeah that is how one of mine is, I believe that one has a Rodime drive
in, which replaced the Seagate ST225N when it quit !

> The hard disk socket seemed quite narrow - was this SASI and does it 
> use a smaller connector?

I believe that the controler end is a 34 way connector as a Floppy would 
have , and at the drive end it has a 50 way like original SCSI. However 
the cable is divided pretty much up the middle with half of the cable 
going to either end of the 50 way, with a gap in the middle.

The other cabling odity is that the floppy connector on the controler is 
a 40 pin, like an IDE cable, which carries both the standard 34 way data 
and the +5V/+12V at one end. This was because the first drives used in 
the Nimbus where weird YE-data 3.5" units which 1/2 height (e.g. as tall 
as a CD-ROM !) and had a 40 way edge connector on them. Later they 
switched to standard format drives, and a cable that only had a 34 way 
cable on it, and a seperate power connector for the drive. It is 
important to get the cable the right way round at the controler end or 
you can end up shorting the PSU :(

Cheers.

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.