4 ms·

Very cool! The more I read about early computing, the more fascinated I become that the major problem innovators needed to solve was memory, not computing per-s

by CamTin 8y ago

Very cool! The more I read about early computing, the more fascinated I become that the major problem innovators needed to solve was memory, not computing per-se. There were precious few things that could be teased into working as read-write memory at electronic computer speeds before semiconductor memory, and they were all monstrously expensive (vacuum tube flip flops, Williams tubes, core memory) or nasty and dangerous (mercury delay lines). Core, despite its expense, was a major breakthrough in that it was solid state and therefore much less error prone. I can't find the reference now, but I remember reading about some early computer engineers (possibly on Whirlind?) contemplating the use of a microwave retransmitting station as a form of memory, essentially creating a "mercury" delay line with microwaves in the atmosphere. This is how desperate people were for anything even remotely affordable which could be tortured to behave somewhat like memory! No wonder Intel made a bundle when they started offering chip memory. The stuff it was replacing was just totally inadequate for the purposes many people wanted to put it to.

Animats 8y ago
The more I read about early computing, the more fascinated I become that the major problem innovators needed to solve was memory, not computing per-se. Exactly. Electronic arithmetic hardware predates WWII. IBM had an electronic multiplier working. ENIAC was a giant plugboard machine. It's not that people didn't think of stored-program computers before Turing. It's that there was nothing in which to store the program. IBM built machines with plugboard memory. Relay memory. Electromechanical memory. Punched-card memory. Punched tape memory. Drum memory. Look at the history of the IBM 600 series machines, a long battle to get work done cost-effectively with very limited memory. Delay line memory was sequential and slow. Willams tubes were insanely expensive per bit. Core memory was a million dollars a megabyte until the early 1970s and didn't get much cheaper. There was plated wire memory, thin film memory, and various ways to build manually updated ROMs. All expensive. Then came semiconductor IC memory (1024 bits in one package!) and things started to move.
xelxebar 8y ago
There are some old giant calculators Friden EC-132s?) that propogated torsion waves down coils of wire for a delay line. This is way out of my knowledge domain, so I'm curious why mercury delay loops were used in the first place.
- Intermernet 8y ago
  "Mercury was used because the acoustic impedance of mercury is almost exactly the same as that of the piezoelectric quartz crystals; this minimized the energy loss and the echoes when the signal was transmitted from crystal to medium and back again. The high speed of sound in mercury (1450 m/s) meant that the time needed to wait for a pulse to arrive at the receiving end was less than it would have been with a slower medium, such as air (343.2 m/s), but it also meant that the total number of pulses that could be stored in any reasonably sized column of mercury was limited. Other technical drawbacks of mercury included its weight, its cost, and its toxicity. Moreover, to get the acoustic impedances to match as closely as possible, the mercury had to be kept at a constant temperature. The system heated the mercury to a uniform above-room temperature setting of 40 °C (104 °F), which made servicing the tubes hot and uncomfortable work. (Alan Turing proposed the use of gin as an ultrasonic delay medium, claiming that it had the necessary acoustic properties.)" https://en.m.wikipedia.org/wiki/Delay_line_memory https://en.m.wikipedia.org/wiki/Delay_line_memory
  - CamTin 8y ago
    Also, they're not "loops" in the physical sense, though they do operate logically as loops: pulses go in one end of the tube, travel through the mercury, and are received at the other end, where they are repeated elecrtonically back to the transducer at the starting end. "Reading" a bit means waiting for the moment when it is hitting the pickup end, and pulling it out of the loop at the same time as repeating to the transmitting end. "Writing" means waiting for the same moment in the "loop" and replacing the output of the pickup transducer with a signal that represents the data you wish to write. Thus, there is an inherent tension between making the tubes longer (more storage per tube) versus keeping them short (lower access times). This tension is inherent to all forms of "delay" memory, including the wire torsion memory grandparent mentions.

by CamTin 8y ago

Animats 8y ago

The more I read about early computing, the more fascinated I become that the major problem innovators needed to solve was memory, not computing per-se. Exactly. Electronic arithmetic hardware predates WWII. IBM had an electronic multiplier working. ENIAC was a giant plugboard machine. It's not that people didn't think of stored-program computers before Turing. It's that there was nothing in which to store the program. IBM built machines with plugboard memory. Relay memory. Electromechanical memory. Punched-card memory. Punched tape memory. Drum memory. Look at the history of the IBM 600 series machines, a long battle to get work done cost-effectively with very limited memory. Delay line memory was sequential and slow. Willams tubes were insanely expensive per bit. Core memory was a million dollars a megabyte until the early 1970s and didn't get much cheaper. There was plated wire memory, thin film memory, and various ways to build manually updated ROMs. All expensive. Then came semiconductor IC memory (1024 bits in one package!) and things started to move.

xelxebar 8y ago

There are some old giant calculators Friden EC-132s?) that propogated torsion waves down coils of wire for a delay line. This is way out of my knowledge domain, so I'm curious why mercury delay loops were used in the first place.

Intermernet 8y ago
"Mercury was used because the acoustic impedance of mercury is almost exactly the same as that of the piezoelectric quartz crystals; this minimized the energy loss and the echoes when the signal was transmitted from crystal to medium and back again. The high speed of sound in mercury (1450 m/s) meant that the time needed to wait for a pulse to arrive at the receiving end was less than it would have been with a slower medium, such as air (343.2 m/s), but it also meant that the total number of pulses that could be stored in any reasonably sized column of mercury was limited. Other technical drawbacks of mercury included its weight, its cost, and its toxicity. Moreover, to get the acoustic impedances to match as closely as possible, the mercury had to be kept at a constant temperature. The system heated the mercury to a uniform above-room temperature setting of 40 °C (104 °F), which made servicing the tubes hot and uncomfortable work. (Alan Turing proposed the use of gin as an ultrasonic delay medium, claiming that it had the necessary acoustic properties.)" https://en.m.wikipedia.org/wiki/Delay_line_memory https://en.m.wikipedia.org/wiki/Delay_line_memory
- CamTin 8y ago
  Also, they're not "loops" in the physical sense, though they do operate logically as loops: pulses go in one end of the tube, travel through the mercury, and are received at the other end, where they are repeated elecrtonically back to the transducer at the starting end. "Reading" a bit means waiting for the moment when it is hitting the pickup end, and pulling it out of the loop at the same time as repeating to the transmitting end. "Writing" means waiting for the same moment in the "loop" and replacing the output of the pickup transducer with a signal that represents the data you wish to write. Thus, there is an inherent tension between making the tubes longer (more storage per tube) versus keeping them short (lower access times). This tension is inherent to all forms of "delay" memory, including the wire torsion memory grandparent mentions.