9 ms·
A vacuum tube ROM?
- greenyoda 8y agoCathode ray tubes were also used as RAM in early computers: https://en.wikipedia.org/wiki/Williams_tube https://en.wikipedia.org/wiki/Williams_tube One of these computers was the machine at Manchester that Alan Turing worked on: https://en.wikipedia.org/wiki/Manchester_Baby https://en.wikipedia.org/wiki/Manchester_Baby
- xellisx 8y agohttp://www.piclist.com/techref/mem/neonlamp.htm http://www.piclist.com/techref/mem/neonlamp.htm
- bjackman 8y agoThere's one of those* on display in the CS building at the University of Manchester, it's the size of a forearm and IIRC stored 1 byte :) * A CRT RAM thing. It's a refreshing RAM that takes advantage of the persistence of the the phosphor glow.
- jacquesm 8y ago"each Williams tube could typically store about 1024 to 2560 bits of data" From: https://en.wikipedia.org/wiki/Williams_tube https://en.wikipedia.org/wiki/Williams_tube
- monocasa 8y agoWilliams tubes don't rely on the phosphar coating (and some don't have a phosphar coating at all). It's all about the static electricity on the tube.
- bjackman 8y agoOh yeah, that's true. Thanks for correction.
- 0xdada 8y agoThey are mentioned in Turing's Cathedral [0], an excellent book that was recommended here on HN. Here's an interesting quote: There were two sources of noise: external noise, from stray electromagnetic fields; and internal noise, caused by leakage of electrons when reading from or writing to adjacent spots. External noise could, for the most part, be shielded against, and internal noise was controlled by monitoring the "read-around ratio" of individual tubes and trying to avoid running codes that revisited adjacent memory locations too frequently -- an unwelcome complication to programmers at the time. The Williams tubes were a lot like Julian Bigelow's old Austin. "They worked, but they were the devil to keep working" Bigelow said. This phenomenon is very similar to the recently discovered row hammer vulnerability of DRAM memory, except it predates it by roughly 65 years. [0] https://books.google.co.uk/books?id=dMK3P6B3WgcC https://books.google.co.uk/books?id=dMK3P6B3WgcC [1] https://en.wikipedia.org/wiki/Row_hammer https://en.wikipedia.org/wiki/Row_hammer
- greenyoda 8y agoThat's a wonderful story! The biography Alan Turing: The Enigma (which I highly recommend) also goes into a lot of detail about the early computers that Turing worked on: https://www.amazon.com/dp/069116472X https://www.amazon.com/dp/069116472X I learned about Turing Machines as a CS student a long time ago, and got the false impression that he was only involved in theoretical pursuits (theory of computation, algorithms for cryptography, etc.). It was only after reading this book that I learned how much he had contributed to the design of actual computing hardware. > trying to avoid running codes that revisited adjacent memory locations too frequently And today, it's exactly the opposite: we try to write code that has as much locality of reference as possible so that we can avoid expensive cache misses.
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- CamperBob2 8y agoVery cool, especially the "SEM with a fixed target" analogy. I've often wondered how the old SAGE terminals handled character generation, and this post fills in the blanks nicely.
- kregasaurusrex 8y agoI'm usually too scared to work with anything over 120V- especially since parts on the schematic linked require a 1000V power supply to work. Very neat, but too dangerous for the average home-gamer like myself to be inspired enough to go out and build.
- raverbashing 8y agoAnd you should be. It can be worked safely if you follow necessary precautions, but unless you are familiar with those, better follow the disclaimer and "do not try this at home". The main issue is that capacitors keep their charge after unplugging, so you might have some that are still dangerously charged. I remember when opening old CRT TVs they had a big notice inside about discharging them before servicing some parts of the circuit.
- CamperBob2 8y ago1000V, at the current levels needed for this application, amounts to the juice behind a good carpet shock.
- kragen 8y agoDunno about the Monoscope in particular, but a lot of tubes need several milliamps, which is quite a bit more painful than a good carpet shock. Not fatal, but not something I'm eager to experience. And I'm the guy who used a one-henry inductor to administer electric shocks to people in high school — including, repeatedly, myself. The issue is that it's a lot easier to build or buy a kilovolt power supply that doesn't have adequate current limiting than one that does. And even one that has it in theory may not have it in practice — that big capacitor across the output? Make sure it isn't just wired directly to the output terminals, because its ESR sure as hell isn't going to be adequate current limiting. So I think it's reasonable to be wary of kilovolt circuits. Dying is easy, but you only get to try it once.
- lightedman 8y ago"The issue is that it's a lot easier to build or buy a kilovolt power supply that doesn't have adequate current limiting than one that does." You can buy Van de Graaf generators all day long. Quarter-million volts minimum for $200.
- NegativeLatency 8y agoCan anyone explain why the letters and characters in the grid are ordered they way they are? A-Z is non sequential, I’m guessing it’s something to do with making character selection logic simpler, but by looking at the letters I couldn’t come up with a definite pattern or rule.
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- Animats 8y agoIt's some variation of BCD code, which was inherited from punched cards and still lives on in some IBM mainframes.[1] [1] https://en.wikipedia.org/wiki/BCD_(character_encoding)#48-character_BCD_code https://en.wikipedia.org/wiki/BCD_(character_encoding)#48-ch...
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- pjc50 8y agoAlmost certainly EBCDIC: http://www.astrodigital.org/digital/ebcdic.html http://www.astrodigital.org/digital/ebcdic.html EBCDIC has discontinuities in the same places, I-J and R-S.
- sprash 8y agoOk... Now I feel the sudden urge to build a working terminal with a Charactron. Why can't I have simple hobbies.
- pjc50 8y ago> video amplifier I used had a gain-bandwidth product of only 4.5MHz. That's .. not really what I'd call a video amplifier, unless the amplifier itself is also made out of tubes.
- SmellyGeekBoy 8y agoIt's tubes all the way down. A series of them, if you will.
- tubetime 8y agogood enough for NTSC or PAL monochrome composite video.
- dfox 8y agoWithout any gain. What is typicaly meant today by video opamp has GBW in low hundreds of MHz.
- CamTin 8y agoVery 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 agoThe 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 agoThere 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.
- sprash 8y agoOriginal catalog entry / advertisement can be found here on page 18: http://informationdisplay.org/Portals/InformationDisplay/IssuePDF/V05N05-1968%20SepOct.pdf http://informationdisplay.org/Portals/InformationDisplay/Iss...