OT Computer Memory (was OT but very useful...)

Larry wrote:
richardcasady@xxxxxxxxxxxxx (Richard Casady) wrote in news:49c969b9.9397015
@news.east.earthlink.net:

Eight bits, one byte, per tube.


I'd love to know the physics behind how they did that. Dual triodes, such as 12AX7, 12AT7, 12AU7, or even earlier 6SN7 were used as latching flip flops, but they only stored one bit...0 or 1. To get 8 reliable levels would be magic. They did use a neon counter tube that had multiple cathodes. Perhaps that is the "tube" that did a byte.



[long nostalgic bit follows...]

Well, this was a slightly mixed memory, I'd say. the idea of 8 bit collections called bytes came later, around the IBM 360 time frame.
Previous IBM incarnations like the 1401 used eight bits plus parity:
6 data, and two marker bits for laying out data fields - if you wanted to add two 1000 decimal place numbers, no problem. Just lay down the field length markers and issue ADD

But computer memories were kinda weird and wonderful.
There was quite a development effort into CRT memory storage:
allocate an X and Y value for each bit and point the electron beam at it to set and to read it out. Hundreds or thousands of bits.
Trouble was the beam position drifted, which didn't help data integrity.

The serial computers used a nickel line for short term storage: you pulsed an electromagnet at one end to set a pulse going for a '1' or no pulse for '0' so a stream of pulses would run down the nickel wire at the speed of sound to the sense coil at the other end, where the data would turn round to the start coil and start over.
That was called magnetostriction.
Others used mercury delay lines. Or coil delays.

Some early boxes used nixie tubes, which were squat little vacuum tubes with ten digits in a clock around the top. It was necessary to kick the glow from electrode to electrode to count from 0 to 9.

But the giant leap from tape drives - first 200 bits per inch, then 650 bpi then 2200 bpi and fixed drum drives to disk drives made the creation of operating systems much easier.
Before that time, there really were operators who would load up a data tape or two and an application program and hit run.
Around 1956, the core memory was a wonderful step forward.
Little ol' ladies really did stitch up 4 kb memories from tiny ferrite rings. Some of them were dunked in a tank of oil to keep the heat down.
Speeds went up fast, from 12 microsecond per cycle, to 4 us to
2 us, then 1.2us then semiconductor chips came along. A big commercial machine might have 64kb, even 128kb.
This was a step back in one way: you could lose power on a core computer and when it came up again, the code and data were still there in core. Not so with solid state memory....

But I'll stop here....
Brian W
.

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