Ken Shirriff Unfolds a Nuclear Missile Assistance Computer System with Impressive Memory
March 25, 2020 No Comments Tech Hacks Jimmy Jones

Longtime fans of [Ken Shirriff’s] work are accustomed to state asking “Where does he get such wonderful toys?”. This time around he’s laid bare the assistance computer froma Titan rocket. To be particular, this is the computer system that would have been found in the Titan II, an intercontinental ballistic missile that you may keep in mind as an essential part of the plot of the traditional film WarGames. Yeah, those siloed nukes.

Amazingly these computers were composed of all digital logic, no centralized controller chip in this baby.

That discusses the requirement for the seven circuit boards which host a legion of reasoning chips, all slotting into a backplane. But it’s not the logic that’s astonishing, it’s the memory. Those dark rectangles on nearly every board in the image at the top of the post are impressively-dense spots of magnetic core memory. That fanout is one of 2 core memory modules that are found in this computer system. With twelve plates per module (each hosting two bits) plus a parity bit on an extra plate, words were composed of 25-bits and the computer’s two memory modules could keep an overall of 16k words.

This is 1970’s tech and it’s incredible to think that when linked to the accelerometers and gyros that made up the IMU this could use dead reckoning to take a trip to the other side of the globe. As always, [Ken] has done an amazing job of walking through all parts of the hardware throughout his teardown. He even includes the contextual elements of his analysis by sharing details of this moment in history near the end of his short article.

If you wish to geek out a bit more about memory storage of yore, you can get a handle on core, drum, postpone lines, and more in Al Williams’ guide.

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