Glass memory?

[Paul Koning]

> On Apr 2, 2022, at 6:27 AM, Liam Proven via cctalk <cctalk at classiccmp.org> wrote:
> 
> On Sat, 2 Apr 2022 at 00:34, Bill Gunshannon via cctalk
> <cctalk at classiccmp.org> wrote:
>> 
>> And, as you say, an Arduino or a Pi that fits in my pocket is orders
>> of magnitude more powerful and costs pocket money.
> 
> The comparisons of size, power, storage, cost, power usage, heat
> output and so on are often made.
> 
> What is less often observed are the facts that a machine that takes
> multiple trailers can be repaired with spare parts. Anything made from
> ICs basically can't, except by replacing the ICs.

But that true for earlier machines, too.  Replacing broken transistors requires having replacement transistors suitable for the circuit in question.  For a 1960s era machine that may be quite hard; while transistors are easy to find, transistors with suitable characteristics might not be.  And what are they?  I'd love to know what the specs of the transistors in CDC's 6000 series "cordwood" modules are.  Other than the stage delay (5 ns) I have no idea.

> What if you can't make ICs any more? Or rather, what level of IC
> fabrication would it be possible to construct from scratch?

That's a fun question and a full answer would probably make a good book.  For transistors the answer is only marginally simpler.  For tubes, quite a lot simpler.  (There's a nice Youtube video of someone making tubes, in his basement.  You need glass blowing equipment, a spot welder, vacuum pumps, and an inductive heating system.  That's about it for tools, as I recall.  Materials: pyrex glass, kovar feed through wires, tungsten filaments, not sure what the electrodes are made of.)

For semiconductors, you'd start with machinery to make ultra-pure materials (silicon, I'd assume).  A Czochralski crystal growing machine to make the cylinders of pure mono-crystal silicon from which wafers are sliced.  Polishing machinery.  Wafer coating machines.  Wafer steppers.  Etching, metal coating, diffusion, etc......... most of which also require very pure and often exotic ingredients.  (I remember being amazed to read that chlorine trifluoride is used as a cleaner in the semiconductor industry.  Look up the properties of that compound, it will blow your mind.)

Reading the specs of the latest generation wafer steppers from ASML (the only company in the world with the technology) boggles the mind, especially if you have some understanding of precision machinery design.  And even earlier generation steppers are not easy devices to make.  I'm not sure what's involved in doing one precise enough for, say, an 1980s era microprocessor.  Or even an SN7400.

Transistors are basically the same as small ICs, unless you go to really ancient types (point contact, mesa, alloy diffusion).

If I had to build a simple computer starting from a pile of rubble I'd seriously consider building it from tubes.

	paul