16 Dec
2015
16 Dec
'15
1:35 p.m.
From the IBM 360/40 functional characteristics:
When IPL is initiated, the selected input device starts reading. The
first 24
bytes read are placed in storage locations 0-23. Storage protection,
program
controlled interruption, and a possible incorrect length indication are
ignored. The double word read into location 8 is used as the channel
command
word (ccw) for a subsequent I/O operation.
When chaining is specified in this ccw, the operation proceeds with the
ccw in
location 16. Either command chaining or data chain- ing may be specified.
After the input operation is performed, the I/O ad- dress is stored in
bits 21-31
of the first word in storage. Bi~s 16-20 are made zero. Bits 0-15 remain
unchanged. The CPU subsequently fetches the double word in location 0
as a new
psw and proceeds under control of the new psw. The load light is turned
off.
When the I/O operations and psw loading are not completed sat- isfactorily,
the CPU idles, and the load light remains on.
I think that the 24 bytes besides covering useful locations in the
bottom of memory may be the minimum record size for the half inch drives.
So you may see 24 bytes or you may see 80. I've been used to seeing a
two "card" boot somewhere, but that isn't the discussion here, since we
are talking probably a cms file. Also may be off in the weeds, as far
as this is concerned.
if you bring up a copy of the VM/370, and convert this to an AWS tape,
on some available CMS drive, you should be able to read it in with some
command line incantation. How you would edit it from there with the
public domain VM/370's editing is anyones guess. XEDIT is licensed, so
you won't have something easy to use to edit and save it if it is a text
file.
By the time you figure all that out, assuming you don't regularly use
either VM/370 or MVS 3.8 on Hercules, or have access to IBM facilities
to use actual IBM products, coding and squinting at your results will
probably produce the result faster. I'm guessing you already have it in
process anyway.
thanks
JIm
On 12/16/2015 12:35 PM, Chuck Guzis wrote:
On 12/16/2015 12:03 PM, jwsmobile wrote:
Does the first block have a PSW looking thing in
the appropriate
start, and an I/O program to boot the next record from the boot
device?
Not to my eye--it starts off thusly:
02 c3 d4 e2 c6
Looks more like 02 "CMSF"
--Chuck