26 Dec
2015
26 Dec
'15
9:54 a.m.
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Mike Ross
Sent: 26 December 2015 01:55
To: General Discussion: On-Topic and Off-Topic Posts
<cctalk at classiccmp.org>
Subject: IBM channel-attached DASD emulation
I've recently been poking about with various bits of emulation with hardware
interfaces... Dave's MFM emulator; various SCSI-to-USB or SCSI-to-SDcard
devices; my Setasi RP12 Massbus disk emulator; the Sigma Seven Lisa
widget/ProFile emulator etc.
What about IBM channel-attached DASD?
The Channel Protocols and Electrical Characteristics of the channel are reasonably well
documented. E.g.
http://bitsavers.trailing-edge.com/pdf/ibm/370/channel/GA22-6974-4_360_370_…
but IBM DASD are complex in that the physical block size can differ from track to track,
and can be changed by the user.
There are various CPUs lying around in private collections and museums
- System/360s; System/370s; System/3 Model 15s; all used channel-attached
DASD: and working reliable disks are much rarer than the damn CPUs!
The ICL2960 at TNMOC at Bletchley used similar disks. It now has emulated disk attached.
I don't think there are any working S/360's or even any that are complete enough
to be restored.
The same goes for real S/370. There might be 30xx or 43xx boxes but those are not 370/s..
Questions:
1. There are or were various 3rd party companies producing rather obscure
emulated DASD replacement subsystems - Virtualblue and Bustech are two
names that come to mind. Has anyone looked into the possibility of using
them to emulate older devices that would be usable on the above vintage
CPUs?
These seem rarer than the original DASD and less well understood. Probably as hard to keep
running as the originals.
2. To those with hardware design experience: how big a task do you reckon it
would be to do this as a home-brew with modern hardware - exactly as Dave
did with his MFM emulator? Is it feasible? Do the entire thing in software - Pi
or Arduino or FPGA - with appropriate driver electronics to drive a channel
interface?
The later IBM channel runs at 4Mbytes/second. Not sure software could keep up.
I've BCC'd some experts with experience - Rich Alderson; William Donzelli;
Henk Stegeman - in the hope that they'll be able to contribute.
What do people reckon would be the best target for emulation? 3340 springs
to mind initially... would that work on machines as old as System/360s? It's
about the *only* option for 5415 DASD...
I think the hard bit is getting the channel protocol working, once that?s running I think
emulating many models of DASD would be possible.
As someone else mentioned Hercules already has code that allows disk files to contain DASD
images in various sector sizes.
It may be possible to use this to talk to a real channel. Implementing some of the channel
protocol in FPGA might be necessary.
But I think finding a real S/360 would be harder...
..... but some one has an FPGA implementation...
http://www.ljw.me.uk/ibm360/
(To digress briefly - a modern reimplementation of
something like the Setasi
Massbus disk emulator would also be very useful; Rich - weren't LCM
working on something like that?)
Mike
http://www.corestore.org
'No greater love hath a man than he lay down his life for his brother.
Not for millions, not for glory, not for fame.
For one person, in the dark, where no one will ever know or see.'
Dave
G4UGM