COMPUTER MEMORIES, Chapter 20

A MEMORY IS BUILT AT LINCOLN LABS, AT MIT
While at Lincoln Labs at MIT, I noticed that as each person arrived at a locked door, they smiled, said hello to the armed guard, then were allowed to enter. That seemed like fun, and since I did in fact had the proper security clearance, but not the need to know, I found my hello and smile worked just fine, so I got to visit places not known to most people.

In one room at Lincoln Labs, I watched them assemble a core memory that consisted of little donuts, smaller than a pencil eraser. There were ladies with a needle, threaded with thin copper wire, and the needle went in the X then the Y directions, then diagonal, with a core at each intersection.

Each “sheet” was about 8 or 10 inches square, and were then hung on the wall like parquet, so as they threaded, wired, then were ready to test, they could touch each and every core with the test probe. When the tests were completed, the “sheets” would be stacked one above the other. Don’t know the intended size of the memory they were building at MIT, but in the early IBM computers, there were 64 cores on a side, a total of 4096 cores on each “sheet,” then the “sheets” were stacked 36 high (plus control and parity bits), to form 4096 memory words of 36 bits each. There were about 150,000 cores per “block” of memory, with wires, wires, wires — each and every one had to be carefully connected.

Aw, one more factoid. The original core memory unit (IBM 737 Magnetic Core Storage Unit) that IBM installed on the 701 at RAND, was in a “box” maybe 15 feet long, 6 feet high, and two feet thick. To keep it cool, the actual “core” memory unit was kept in a pressurized tank of oil. When there was a problem, they had to first remove a bunch of bolts, lift the lid, then use the built-in crane to lift the memory out of the oil, let the oil drain for an hour or two, then look for the problem.

I don’t know why I remember this at all, and I hope it is at least approximately correct. I remember the monthly rent for 32,768 words of 36 bits (the equivalent of 196,000 characters), was about $20,000 — Google says $6,000, but then who’s counting! Purchase price would have been maybe 40 or 50 times the monthly rent. (Don’t take this as absolutely correct, I didn't say the cost was $20,000, I said that is what I remember as the cost. It’s just a faint memory.)