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Mainframe Memories

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At the time of writing, it is approaching the 50th anniversary of the announcement of the IBM System/360 aka "The Mainframe". By now, anyone who's been even tangentially involved with this beast is familiar with the number of times it's been written off: most notably in 1991 when the prediction was made that the last mainframe would be switched off in 1996.

 Of course, that never happened.

There have been notable losses, including one site dear to my heart, but the mainframe has one thing in common with Mark Twain: "rumors of my death have been greatly exaggerated". Indeed since Linux became available on the platform, the mainframe has shaken off its "legacy" (how I loath that term) badge and is at the leading edge of innovation.


I started with my first mainframe in 1981, when I received a cadetship at the New South Wales Totalizator Agency Board (aka TAB). This was the state government's off-track betting agency which had set up a computer science cadetship scheme where high school graduates would work part time and do university part time for two years before doing the final two years of a Computer Science degree full time. This was a wonderful scheme, the brainchild of its former CEO, the late Allen Windross.

Although 1981 was the first time I ever got to touch a mainframe, it was a few years earlier that I was first exposed to the technology. I started my high school's basketball program when I was in year 9 and as part of getting it off the ground I scrounged for equipment and supplies wherever I could. One lunch time I was given the okay to go into the sports' storeroom whereupon I came across a box full of manuals and correspondence.

I don't know how they ended up where they did but in that box were IBM manuals including an introduction to System/360 (S/360), a self-paced assembler course, functional manuals of the S/360 model 20 (sometimes referred to a S/360 in name only), a 1401 Autocoder manual, and the minutes of the local S/360 user group.

Over the next couple of years I taught myself assembler and COBOL but had no way of seeing if the programs would even assemble or compile. No matter, I was smitten with the technology.
As part of the cadetship I was required to work all three shifts in the computer room for three months during my first year. In those days the shifts were 3 x 8 hours starting at 8am, 4pm and midnight. Consequently, I was able to work with a variety of equipment.
For the hard-core geek here's a run down of the equipment I encountered during my 18 year stay with the TAB. Thanks go to Phil Steele who compiled the list of equipment.

System/360

S/360 Model 44 - we had two of these, the only other two in the country were at the Pine Gap facility in the Northern Territory. These were grand beasts, complete with flashing light front panel and golf ball typewriter console. These were acquired in 1971.

The configuration included:

  • Each processor had 128K memory storage and operated in dual, master/slave, modes. During the system set-up the storage was extended to 256K each. The software used the IBM Assembler language and eventually ran a specially customised version of DOS Release 19. (Programmers had to get special permission to use storage-to-storage instructions as these were emulated on the '44.)
  • Four IBM 3967 telecommunications processors (which I think were special purpose S/360 processors, but I could be wrong. In any event they had that remarkable TROS technology).
  • 12 IBM 3970 telecommunications adapters.
  • 5 IBM 2314 disk drives for each central processor.
  • One IBM 2415 magnetic tape drive for each central processor.
  • One IBM 1403-N1 and One 1443-N1 printer (shared via 2914 switch)
  • One IBM 2501 card reader for each central processor.
  • One IBM 1442 Card Punch (shared via 2914 switch - note this picture's from one on sale on eBay!)
  • One IBM 2848 visual display unit controller for each central processor supporting six 2260 VDUs.
  • Two IBM 1053 golf ball type printers.
  • Model 29 card punch

The 44's were fun to operate: front panel lights always made you feel like real work was being done. One story I only came across recently, states that a ruggedized redundant version of the 360/44, the System/4 pi, flew on the space shuttle. Supposedly they whacked an axe into it for a demonstration and it kept running.
A novel feature of the 2314 was that their addressing could be changed by moving magnetic plugs on the front of the drive.

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