Paul Koning pkoning at
Wed Jul 6 08:23:01 CDT 2005

>>>>> "Brad" == Brad Parker <brad at> writes:

 Brad> Vintage Computer Festival wrote:
 >> In the old days, IBM was stupid and didn't want anyone to learn
 >> about their computers.  They kept them locked up behind glass
 >> walls where one could only drool over them, and only let
 >> priveleged people touch them.  So

 Brad> My experience is the S/360 & 370's machines ran 24x7 and there
 Brad> was little time left over for hacking.  But if you got to be
 Brad> friends with the operators and read all the manuals and what
 Brad> source code you could find, you could do some pretty fun hacks.

I've had some operator time in college on a 360 model 44 (running
OS/PCP, which was unusual since most 44s ran an OS specific to that
machine -- it didn't normally have a full 360 instruction set).  It
belonged to a nearby grad school, and didn't run anywhere near 24x7.
So powering it on and off was part of the experience.

I had some fun hacks on it.  The console wasn't considered a normal
I/O device (it had no name so programs couldn't reference it in the
usual way).  But if you constructed a few of the relevant data
structures "by hand" you could read/write it just fine.  So I messed
up all the UI conventions by doing exactly that.

The other hack was a switch into supervisor mode from my application
(the WATFOR compiler, actually...) to install a patch into the kernel
to capture an interrupt (some operator panel button).  It was really
easy, quite obvious from reading the manuals.  I found out later in
grad school that the same security bug was still around in OS/MVS
21.x.  Didn't use it there (verified it existed but resisted the
temptation to exploit it).

Lastly, there was the 360 program for reading and printing PDP-11 DOS
formatted tapes... including search by name, something OS/360 could
not do even for native tapes...  I wish I still had that program, but
no such luck, not even a listing.

So yes, you could hack those machines if they weren't too large and
you were in the right spot.  But I'll agree that I'd grab a PDP-11 way
before I'd be tempted by a 360.


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