The IBM S/360

The IBM System/360

In 1966, the bank I worked at in Boston got one of the first IBM System 360's. We had a Model 30, a small one. I think it had 64K of memory - this was the first system IBM made with the 8-bit characters, and the word byte came into being. There were several other innovations, too - our Mod 30 had disk storage drives. We had 2311's, which were about 3' tall. The big disks (about 18" in diameter, and 7-8" tall), which you removed with a plastic cover that locked over the disk, each stored an incredible 7.5 MILLION bytes! Another advance over the 1401 was the Selectric typewriter console (you can see it in the picture), so you could actually type in number and letter codes; you didn't need to enter them with toggle switches. The 360 still used card readers, punches, tape drives, and the same kind of chain/train printers that came with the 1401. But everything was faster, sleeker, compatible across the whole 360 family - there were lots of different models - and, incredibly, not much more expensive. No wonder the IBM S/360 quickly became the de facto standard of computing all over the world.

Software

The first "operating system" I ran on the 360 was BPS, the Basic Programming System. You loaded it with a deck of punched cards, and it would prompt you to enter instruction codes and job control and so forth. BPS was followed by BOS (Basic OS), TOS (Tape OS), DOS (Disk OS, pronounced "dee-oh-ess," never "doss"), and finally by mighty OS, which turned into MFT, MVT, and today's MVS (which I guess is being replaced by OS/390). This DOS and OS had nothing to do with today's DOS and OS/2, although the parallels are there. Mainframe OS was objectively much better than DOS, but lots of companies were very slow to move because there was a conversion involved, and usually a hardware upgrade. All us IBMers (by this time I'd become an IBM salesman) were out trying to convince customers to upgrade. The big difference was there was no Windows alternative. I guess Bill Gates would have been in grade school at that point in the history of computing...

On-Line Systems

What the bank got the 360 for was to set up one of the first on-line systems. They put Teller Terminals in the bank branches, and the tellers could look up people's accounts in real time, and transactions could be posted to the accounts as they happened, instead of waiting overnight for the posting run. These early commercial on-line systems (by this time, on-line systems were old hat to the government, military, and university communities) were very fragile. As the night shift operator at the, bank, I spent a lot of time trying to get the branch terminals logged off properly for the night. When things got screwed up, you could never figure out if it was the 360, the software, the phone line, or the terminal at the other end. Sound familiar?

Large S/360 installation

This is what a big 360 computer room looked like. In the front is the CPU (this looks like a Model 50, but they all looked pretty much alike, just that the bigger, more expensive models had more dials and switches on the front) and operator console, with selectric typewriter. Just over the operator's head is a bank of 2311 disk drives. This bank of 6 disk drives would have held almost 50 million bytes of information on-line at once. This was mind-blowing back 30 years ago! Behind the CPU you can see the tape drives. In those days, the system would have still had a card read-punch (probably a model 2540), but I don't see it in this picture. Far in the background are other computers, storage, and control units.

If you have stories to share, or you've spotted some errors in my recollection of how things were back then, please write me at denichols@ridgefield-ct.com.

Buy IBM's 360 and Early 370 Systems
by Emerson W. Pugh, Lyle R. Johnson, John H. Palmer

Buy Computer Architecture : Concepts and Evolution
by Gerrit A. Blaauw, Frederick P.Brooks
I've had the pleasure of working briefly with Dr. Fred Brooks, one of the architects of the S/360. Read this key book by one of the great men of computing!

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