Date   : Wed, 24 Jun 2009 09:28:19 -0500
From   : jules.richardson99@... (Jules Richardson)
Subject: reading data from old hard disk

Phil Blundell wrote:
> On Tue, 2009-06-23 at 22:55 +0100, Ian Wolstenholme wrote:
>> If it's from an HDFS, can it not be connected up to the MDFS somehow?
> 
> Not easily, I don't think.  
> 
> The M2235 disk uses an ST-506 interface and is presumably formatted with
> 256-byte sectors since this is what its documentation seems to assume

ST506/412 drives were typically formatted 256x32 or 512x17 IIRC, although 
there was nothing that said you *had* to do this (a controller was free to use 
a lower - or even higher - SPT value if it wanted)

> Even leaving aside the sector size problem, you'd need to find a bridge
> board that would interface ST-506 to SCSI (not SASI) and that was
> completely transparent, without needing the host to send any special
> initialisation sequence.  I'm not sure if such things exist or not.

 From memory, the Xebec boards could be fitted with custom firmware to do the 
initialisation, or they could accept a Xebec-specific (SASI) command at 
startup to do it. I believe the OMTI boards always needed the user to do it 
via an OMTI-specific (SCSI/SASI*) command.

* I think the OMTI boards are all SASI, but I could be wrong. I've got a big 
book 'o bridge board manuals, but of course it's still stuck in England!

The Adaptecs (all?) worked by storing geometry on sector 0/0/0 (which should 
always be reachable regardless of real drive geometry) and then masking this 
sector from the user during normal operation. The Adaptec bridge manuals are 
probably on bitsavers - I don't recall what the exact mechanism was for 
'hiding' this configuration sector from the user during normal post-init ops.

There might be issues in moving an Adaptec-formatted drive to a Xebec/OMTI 
board (and vice-versa) and reading raw blocks - even assuming the low-level 
bitstream format's interchangeable.

cheers

Jules