from Dave Cortesi (10/2004)
... the /30 was the smallest of the line to support the 360 API.
There was also a 360/20, but it had a different instruction set.
The /20 was intended as a machine to upgrade customers who ran "unit
record" accounting shops based on the 402 and 407 punched card
accounting machines. These customers were assumed not to be interested
in general programming or in using tapes or disks.
The /20 was optimized for reading cards and printing reports, and was
almost exclusively programmed in RPG -- a language that embodied all
the concepts implemented in the 402 and 407, based on sequential
processing of pre-sorted records. Although the /20 was called a "360,"
used SLT, and had the same cabinet styling, it was not a 360 in the
sense of being upward-compatible with the /30, /40, etc.
The 360/30 was intended to be the natural upgrade for accounts with a
1401 system. The 1401 was a general-purpose computer with what was at
the time seen as a massive base of existing software. To that end, the
360/30 could be had with an optional 1401 emulator feature to run 1401
software in binary (well, in decimal actually) direct from tape or card
decks. Early on, short-sighted customers and salespeople ordered a lot
of 360/30s with 16K of memory -- because that was the maximum the 1401
could have, and who would need more?
But if your system had the full 64K, DOS/360 let you "partition" it
into two or even three partitions and load 2 or 3 concurrent jobs.
While it did actually work, this was very seldom actually done. The JCL
to accomplish it was tricky; plus each program had to be linked to the
hard starting address of the partition in which it would run; plus, the
reader and printer had to be assigned to a single partition, there was
no spooling software in DOS; and all console output came out on the one
console typewriter, mixed together line by line.
Concurrent jobs did become feasible in 360/30s and 360/40s a couple of
years after introduction when two software guys in the SF Bay Area --
sorry I don't remember their names -- implemented a spooling add-on for
DOS, giving each of the three partitions a virtual reader, punch, and
printer, multiplexed onto the real hardware.
I don't remember the names of those two guys, but I do remember the
day I was introduced to the brilliant idea of SPOOL: Simultaneous
Peripheral Output OnLine.
from John Fryatt (March 2005)
I was just digging around for IBM System/360 stuff and found your site.
I operated a 360/30 in the 70's. It had 32k of core memory built in,
plus another 32k in a third-party add-on box. This 32k stood about 5'
tall and 2'6" square!
The model 30 was *not* the smallest 'real' 360. Another local company,
whose machine we used at night, had a 360/25. This ran the same
instruction set as the 30 as we loaded our programs into it.
We originally ran the BOS operating system, then upgraded to DOS. We
also later got a spooler, GRASP, so we could run three partitions,
although GRASP itself occupied one of them.
BOS was very limited - all console messages, for instance, were
four-character codes which had to be looked up in book to make sense of.
Of course, the old hands knew them anyway, but if any problem occurred
there was little you could do except re-IPL the machine. DOS was a great
improvement.
Odd things spring to mind, like the 2311 disk drives jigging around as
the heads moved in and out. These drives were very heavy engineering by
todays standards. Also, the machine room was very noisy - you got used
to it and didn't notice until you powered the system down at the
weekend, and thought you'd one suddenly deaf!
The 1403 line printer had a great feature, which was a powered lid that
opened when the box of paper was almost used up. The resulting
cacophony, as all the little slugs in the print train hammered on the
ribbon and paper reminded the ops to load a new box.
For a long time we did data input using punched paper tape, which was
pretty archaic even then, but did eventually move to key-to-disk
equipment and data input via magnetic tapes.
One trivial detail I could never work out the reason for was that on the
model 30 the lights on the console were behind number-shaped cut-outs,
whereas every other model 360 I saw had little round plug-in lights on
the console.
from Dan Espen (October 2007)
While the comment about the 360/25 being a lower end model is correct,
the 360/25 was introduced quite a bit after the initial 360 line.
Another reason 16K wasn't enough for the 360/30 is that you could pack
a lot more logic into the 16K of the 1401 than the 360/30 even when
coding both machines in autocoder/assembly language. I made that
comment to my boss when we considering a 360 and had the IBM reps
show up and challenge me in front of him. I was able to explain in
detail why that was true. I was around 20 years old at the time.
Ed Thelen says - I bet that was fun! I'm glad I wasn't in the shoes of
those IBM reps :-((
[Follow up]
A little fun and a little disappointing that my boss wouldn't believe me.
Found out when I left that they had IBM checking up on everything I did. Being young
it took me a while to realize how clueless a boss can be.
from Charlie Cleveland Dec 2007
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Hi Ed,
WOW !!!
I just read your 360/30 page. I am amazed at the memories it conjured.
Gosh, I haven't heard the term ' IPL' in decades.
While going to school to learn programming (1970, they had a 360/30),
I was working as an operator at a shop (they had a 360/25) in the Wash DC area.
After graduating, I acquired a position as an operator at an insurance company (360/30).
A year and a half later, I finally landed a programming position (COBOL)
with a contracting firm (very fortunate for me as this company was started by the people
who worked with Grace Hopper, the "Mother of Computers"). During this time,
I realized that the 360/30 was by far the most widespread machine in the DC area.
I recall the 1401 emulation both as an operator as well as a contractor.
As an operator, I used the '// FETCH' JCL (I don't recall the parameters) to initiate
the 1401 emulation. You also had to turn off the I/O check at the CPU (this was
because the 1401 allowed a multi-punch in rows 4 thru 7 whereas the 360 did not).
As a contractor, I had to convert some systems from 1401 to 360. I recall, in the 1401 world,
the sign (+, -) was located in the high order byte, wherein the 360 and
all subsequent worlds, the sign is located in the low order byte.
I remember the partitioning and spooling. It seems to me, we used two programs in this area,
DEBE and DITTO. I believe DEBE was a print spooler and DITTO was a general utility (not sure).
One short story during my time with the insurance company as an operator:
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From time to time I had to go into the stock room for printer paper. I noticed
there was a small box on the top of one of the shelves. After several month's, I decided
to check it out. After blowing off a 1/4" of dust (this box was ancient even in 1971), I realized
that I had found an "IBM Port-a-Punch". I asked the DP manager if I could have it and he said OK.
Over 36 years later, I still have it here in my office in the original box.
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What a wonderful site this is.
Thank you so much for the moment of fond memories you have inspired.
au,
Charlie Cleveland
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