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The forgotten story behind IBM's 'first mainframe'

Rupert Goodwins ZDNet.co.uk

Published: 07 Apr 2004 15:15 BST

It's hard to list all the ideas that Stretch embodied and that have since become canon law in processor design. It could fetch and decode multiple instructions simultaneously -- remember the superscalar hype of the late 90s? -- and pipelined them, decoupling decoding and execution. It could predict the results of calculations and speculatively execute code depending on its best guess, and could look ahead to unexecuted instructions to make the best use of its internal resources.

These are ideas still essential to the best that Intel produces and the Stretch did them all with around 170,000 transistors. The last chip that Intel made with so few active components was 1982's 80286, which is a part remembered these days -- if at all -- for not needing a heat sink so much as a mop to get rid of the drool.

Alas, none of the above proved enough to match the promises made by IBM's marketing department. Stretch was delivered a year late and substantially more slowly than predicted. It was still the fastest computer in the world and remained so until 1964 but by then the market for high-performance computers had changed. Ten were made, going to atomic research institutes and spooks: the S/360's first customers were banks and airlines. There was a plan to build directly on the Stretch architecture, but that got canned. Although a commercial failure, Stretch was nonetheless IBM's best investment in research and development -- an exercise that Steve Jobs was to repeat 30 years later with the proto-Macintosh, Lisa.

All of which left some of the chief designers free to do other things. John Cocke, one of the brains behind the simulator and a true genius in many fields, took what he'd learned and what he hadn't been able to get through, and eventually ended up with an idea called RISC. IBM adopted that wholeheartedly with the PowerPC architecture, as did others such as Acorn, with its ARM processor. If you own a modern IBM mainframe, a mobile phone, a set-top box, an Apple or even an iPod, you'll possess some of the spirit of Stretch. The modern PC, needless to say, would simply never have happened otherwise.

So, while you toast the success of the S/360 -- another small sherry? -- remember that it and almost everything else you'll touch with a chip inside is the inheritor of a burst of unmatched innovation, one that flowered years before, in the unholy light of Trinity.