Metres To Millimetres

If we shrink down by a factor of a thousand, we arrive at the millimetre scale, where an ant is pretty big stuff. This is about the limit of what the human eye can effectively see unaided, or the human body can manipulate without mechanical assistance, so it's a convenient milestone on the road to Lilliput.

Here's an example of millimetre scale technology. This, for those of you too young to remember or old enough to have had enough bad experiences and deliberately forgotten, is a vacuum tube.

If you examine this device closely, you'll see that its fundamental geometry: the spacing of its grid wires, the distance from the cathode to the plate, are all on the order of millimetres. With the development of electronics, device scaling immediately became important: the smaller you made a tube, the faster it ran and the less power it used. Unfortunately, the fact that tubes had to be assembled from separate metal parts limited how much you could shrink them.

This particular tube is a 6SN7. That's the type used in the flip-flop circuit of the ENIAC, the world's first electronic digital computer of 1946. Each tube, along with a handful of other parts, stored one bit of computer memory--RAM. The ENIAC contained 18,000 tubes like this, occupied 3000 cubic feet of space, and required 140 kilowatts of electricity. It had about the computing power of a pocket calculator. It was a miracle of millimetre technology.

Tubes like this aren't even made in the United States any more; this one came from the Soviet Union and cost $13. Interestingly, that's almost exactly the current price of an 80 nanosecond 1 megabit dynamic RAM, with a million times the storage capacity and 125 times the speed.