Reading ESDI disks

Paul Berger phb.hfx at
Thu Feb 11 15:43:48 CST 2021

On 2021-02-11 4:31 p.m., Mattis Lind via cctalk wrote:
> Den tors 11 feb. 2021 kl 20:36 skrev Fred Cisin via cctalk <
> cctalk at>:
>> On Thu, 11 Feb 2021, Mattis Lind via cctalk wrote:
>>> What is the best way of dumping the contents of an ESDI disk?
>> Same as for ST506/412
> I usually use David Gessweins MFM emulator for dumping unknown MFM disks.
> It works perfectly!
>>> I have an original IBM Enhanced ESDI ISA controller board. Could that be
>>> used under Linux? Or NetBSD/FreeNSD? I googled but didn't find much.
>> Do you have suitable drivers?
>> Yes, ESDI has been used with Linux.
>> In some cases, probably including the IBM ESDI controller, it looks
>> similar to the computer as an ST506/412 setup.
>> Start with another drive, and get your controller, drive, and OS working
>> with each other as ordinary drive, BEFORE trying to read an alien disk
>> using them.  It is generally important to isolate variables, so that you
>> can determine whether problems are your setup or are problems with the
>> alien drive.
>>> Is there any other way of dumping the disk contents?
>> IS IT THE SAME controller that the drive was written with??
>> If so, no problem.
>> If not, PROBLEMS.
> The drive was written by the very same controller, yes. The controller was
> in a IBM RT PC that had a battery explosion. The ESDI controller may have
> survived along with the disk. So the question is there drivers for this
> board in anything else then a RT PC?
> Chuck is saying that the ESDI command set on the controller level is
> identical to ST506 controllers.  Anyone with experience of the "IBM
> Enhanced ESDI controller"?
> I did a fair bit of googling but it didn't turn up much when it came to
> Linux support. Of course,  if it is the same as the ST506 AT controller
> then it should work out of the box.
> But then I thought, perhaps this is a more generic problem. People having
> ESDI drives (well, SMD as well I guess) that there is no controller
> available for or could be made running due to drivers or whatever. So what
> if those drives could be read anyway.
> Interfacewise it shouldn't be that complex. One benefit of ESDI is that the
> clock extraction has already been done, so it is mostly a question on
> finding marks calculating CRC.
> /Mattis

I do seem recall using ESDI drives in a PC with 16 bit ISA slots but it 
is a long time ago but I am not sure if the controller used was the RT 
controller you have pictured, it seems to me the one used was a Western 
Digital controller.  I do know for sure PS/2 had a microchannel ESDI 
controller.  I suspect teh ESDI controller is at least similar to the AT 
ST-506 controller as some RTs had the AT ST-506 controller in them, in a 
former job I upgraded several 6150s that had the original NMOS processor 
to the newer CMOS enhanced processor and also changed disks from ST-506 
to to the huge 70MB ESDI drives.


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