IBM channel-attached DASD emulation

Tom Gardner t.gardner at
Sun Dec 27 14:15:15 CST 2015

Actually the DASD themselves are easy to emulate when fully buffered and
error free as IBM does today in its mainframes.


What is really hard to emulate is the Storage Control Unit and the
appropriate set of CCWs associated with a specific Storage Control Unit and
attached DASD. If I were doing this I might start with the 2314 DASF; it
might run on any Selector or Block Multiplexor channel and since the tracks
would be fully buffered in memory there really is no performance issue since
there would be no seek time or latency time.  For the command set to emulate
see, Initial CKD implementation
on Wikipedia or the 2314 reference manual.   If there was more than one
device on the channel u might have some serious hogging issues 


The 29MB/spindle or 232 MB/facility might be a limitation on some of the
newer systems, but it is possible to modify IBM's Oss to change the
characteristic of a DASD to almost anything by changing the device
characteristics in a table of such - that's how the PDMs attached double
capacity 2314s and 3350s; they redefined an unused device, e.g. 2311, to
have the characteristics of these non-IBM supported devices.  In this case
all one might have to do is redefine the 2314 characteristics


The full step which would be really really interesting would be to build an
emulator that could operate as a Selector/2314/2318r, BMux/3380-2/3350
and/or (Bmux and Escon) /3990/3390.  All together IBM implemented 83 CCWs
for its CKD DASD, most but not all of which would have to executed by such
an emuiator.




-----Original Message-----
From: Paul Koning [mailto:paulkoning at] 
Sent: Saturday, December 26, 2015 11:15 AM
To: General Discussion: On-Topic and Off-Topic Posts
Subject: Re: IBM channel-attached DASD emulation



> On Dec 26, 2015, at 4:54 AM, Dave Wade < <mailto:dave.g4ugm at>
dave.g4ugm at> wrote:


> ...

> but IBM DASD are complex in that the physical block size can differ from
track to track, and can be changed by the user.


>From sector to sector, actually.  And sectors can have key fields along with
the data -- the device will find a sector by key match on a track.  





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