26 May
2005
26 May
'05
12:55 a.m.
Tom Jennings wrote:
Slightly changing subject (!), but remaining on
discretely
constructed memory, one truly practical memory that was tried and
abandoned about 1952 (one of the Standards computers) was a
switched capacitor memory. It was umm revived some years later and
is now of course universal.
A discrete-capacitor, diode-switched, dynamically-refreshed memory
was built and tested and performed apparently well was built for
SWAC? SEAC? or something in 51, 52 [ref in Huskey's COMPUTER
HANDBOOK] but abandoned as solid-state diodes were prohibitively
expensive.
It would clearly be most straight-forward to build one today, even
with el cheapo ceramic disks. Probably could do .25 sq in per cell
on a PC board. And since one was actually made, it would be
historically correct.
Don't forget discrete-capacitor dynamically-refreshed memory was pioneered by
Atanasoff for the ABC in 1939-41, albeit mechanically accessed (rotating drum, 1500 bits,
max access time 1 second).
One of my languishing projects is a recreation of the ABC prototype (2 registers of 25
bits (capacitors) each on rotating disc, together with serial RVL[1] adder/subtractor.
(Although such a recreation was already done for the Honeywell vs. Sperry-Rand trial in
the 70s).
[1] RVL: Resistor-Vacuum-tube-Logic - the original electronic logic family :)
... recently received a counter using Philips E1T[2] tubes. Not overly useful as a
general-purpose memory but it is a state-holding device (3.3 equivalent bits), and another
example of the bizarre-by-today's-standards techniques from the pre-IC days.
[2] E1T provides similar functionality to dekatrons - one tube providing combined
functionality of decade counter and display - but entirely different technology. The E1T
is based on an electon beam held in 1 of 10 places (states) by a combination of
electrostatic and magnetic fields. The beam can be shifted from place to place with pulses
to accomplish the counting function. Beam then hits a flourescent screen in accordingly
different spots for the 1-of-10 display.