Bob Lester wrote:
> Do you know if the 360/75 was a common machine at the time?
> I worked as an operator on a 360/75J (and a 360/30).
The System/360 Model 75 was not an UNcommon machine (as were
the Models 91, 95, 85 and 195) but it was not exactly common.
Only VERY large shops would feel the need for one. NASA had
five which were used to support the Apollo moon program. And
lots of universities had one or two. For businesses, a 360/40
or 360/50 were "common." Big businesses might have a 360/65
or two (instead of a 360/75, since it was almost as fast, but
much cheaper). The Model 75 was the smallest machine that
implemented the System/360 instruction set in hardware, so
it was correspondingly expensive.
Without memory, a bare 360/75 cost ~$1,012,860 in 1965 $$$s.
Memory was ~$1.54 per byte, so a 360/75 J (1024 KB or 1 MB)
would have cost $2,583,860 (approximately). But very, very
few customers actually purchased computers from IBM at that
time. The vast majority simply rented them. The third-party
leasing business had not yet arrived on the scene. Here is
what a typical 360/75 configuration would have cost a "real"
customer (that is, not an educational institution, to whom
IBM rented equipment at a 40% discount) in August of 1968:
$ 39,308 2075 360/75 CPU
63,532 (4) 2365 256 KB core storage units (1024 KB)
12,875 (5) 2860 Selector Channels
4,460 (1) 2870 Multiplexer Channel
1,050 2150 console attachment + 1052 console typewriter
36,060 (4) 2314 Disk Facility (8 drives ea.)
2,000 (100) 2316 Disk packs (for 2314s)
5,278 (1) 2401 + (4) 2402 tape drives + (1) 2803 control unit
4,808 2821 control unit + 2540 card reader/punch
+ 1403 printer + 1416 print train (see note)
6,590 2703 "Teleprocessing" (TM IBM) Control Unit
17,300 (100) 029 keypunches
0 OS/360 software + compilers + any other programming
0 (2) resident, on-site IBM System Engineers, dedicated
to the customer, to support the SCP software, and any-
thing else that the customer wanted them to do.
0 (5) resident, on-site IBM Customer Engineers, whose
job was to bang screwdriver handles on the floating
point card cage at 4 AM when the machine red-lighted
and machine checked.
--------
$193,261 Total (that's PER MONTH, boys and girls, in 1968 $s)
(NOTE: It was asserted in the IBM anti-trust trial discovery
that IBM made more PROFIT on RENTAL of JUST print trains for
IBM 1403 printers than the GROSS revenues of ALL of the other
computer hardware vendors that competed with IBM - combined.)
In those days, the software was "free" (i.e., no extra charge).
People were cheap, hardware was expensive. In terms of its raw
instruction processing power, a 360/75 had about the computing
capacity equivalent to an Intel 80286 6 MHz processor (the IBM
PC/AT used a 6 MHz CPU when it first shipped in 1982). But the
360/75 had 1.2 MB/sec channels, and it could support 6 of them.
The PC/AT or indeed most Intel-based systems up until recently
would have had a hard time keeping up with the 57.6Mb/s data
transfer rate of a 360/75 (or 360/65, which was equivalent).
Those 256KB 2365 core storage units were an amazing piece of
gear. Core density was 455 bits/cubic inch. They sucked power
and generated enormous amounts of heat. You could fry eggs on
the heat vents (and yes, we did that more than once, just to
show off for folks who were not impressed by the size of that
beast alone, all 10 frames of it [for just the CPU+memory]).
> Seems to me that ours ran MFT? (later MVT?).
That might have been the case. The first release of MVT was
OS/360 Release 13 (FCS 08/14/67) but MVT didn't get its act
together until Release 17 in 1969. So most folks continued
to run MFT-I (Release 14 CMR) -- or MFT-II (Release 15/16) --
until about 1970 or '71 when Release 18.6 became available.
> This would've been around 1979.
Only universities and IBM itself, plus folks who had actually
purchased a 360/75, would have been using one as late as 1979.
If you were renting one (the only other option available from
IBM at that time), then you long ago moved on to both faster
and cheaper (via leasing, which was now getting started) gear.
By the end of 1971, 360/155 and 360/165 boxes were displacing
the high-end S/360 boxes, and the 370/145 was displacing the
low-end S/360 boxes. I know that the University of Waterloo
kept their (famous) Model 75 around for a long time, but by
1974, basically, they were becoming as rare as hen's teeth.
Unless you worked in such a place, I really doubt that you
were operating a 360/75 in 1979.
In fact, so many 360/50 machines were being returned to IBM
(off rental), being replaced by either a 370/155 or 370/165,
that IBM was able to plan to build all core memory units for
the 370/165 processor from used (although re-built with new
electronics) 360/50 core memory. It took 4 of the usual size
(512 KB) 360/50 machines to get enough core memory (2 MB) for
the smallest 370/165. There was enough to go around. IBM, in
fact, sent the vast majority of their off-rental 360/50 core
memory to the landfill (for tax/depreciation reasons). They
were happy to do so, because 360/40 and 360/50 customers were
snapping up 370/155 boxes like hotcakes. A bunch got a hold
of 370/165s as well, but unfortunately too many folks leased
or bought one outright. (Both of these boxes were later to
be deemed boat anchors when the OS/VS1 and OS/VS2 SVS + MVS
announcement was made, since the "DAT box" upgrades to them
were so horribly expensive.)
--
WB
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