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Thread: Tube computer size: ENIAC vs Bendix G15

  1. #1

    Default Tube computer size: ENIAC vs Bendix G15

    My dad mentioned to me the first computer he used was a Bendix G15. I looked it up, and was surprised it was vacuum tube based, given its small size. Huge by today's standards, but when I think about vacuum tube computers, I think of building sized computers like ENIAC. the ENIAC is usually regarded and the first tube based computer. Why was it so huge and complicated? Why not start with a simpler design? Were they going all-out to try to make a megacomputer, or were they really incapable of coming up with a simpler or smaller design?
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    Quote Originally Posted by carangil View Post
    Why was it so huge
    ENIAC was built using very large components, octal-base tubes, for example.

    The MIT Whirlwind was a multi-story building, using similar packaging density, built a few years later but much more complicated.
    It was actually a stored-program computer.

    The G15 used much smaller tubes, semiconductor diodes, and was a much simpler design (serial instead of parallel arithmetic, for example).

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    We have a Bendix on display at the VCF museum in New jersey. It is very amazing how small it is compared to the Univac across the isle or the Cray a few feet away.

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    Serial operation and lots of diodes. Drum memory also keeps the need for active circuitry down.

    Look at the Litton 1601 for an example of a minimalist 1970s serial drum-based computer. Since it used commodity TTL and not much of it, it would be an excellent candidate for a retro PC. Earlier versions (made by Monroe) used discrete components and still were small. The PB250 likewise used very few active devices and used about 1500 Watts and could be placed on a table. Basically, you only need active devices when you need to implement the NOT function.

    Too bad, the old stuff doesn't interest many VC people nowdays. History appears to start with the microprocessor.

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    Hi All;

    "" Why was it so huge and complicated? ""

    There are many reasons, some of which were the large tube Size.. But, it was also this was the first Electronic Digital Computer and they didn't know what We know Now..
    They had to work out not only what it would do, but how to accomplish getting that done and it took time to build..
    There was no Stored Program, type of Architecture, and the Military kept changing what they wanted it to be able to do..

    There is a Fairly New Book out On the ENIAC, which I have.. It's Title is --
    "' ENIAC in Action "" Making and Remaking the Modern Computer
    By Thomas Haigh, Mark Priestly and Crispin Rope..
    MIT Press 2016..

    And here is the Video to go along with the Book..
    https://www.youtube.com/watch?v=3Z8XrC3kLJM

    THANK YOU Marty

  6. #6

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    My dad was a civil service DP manager and when I was about 12 he took me to see his "office", where there was one of these: http://www.ed-thelen.org/comp-hist/BRL61-0448.jpg

    It's an IBM 705 full of 9-pin miniature vacuum tube modules.

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    Subminiature (T3 outline) tubes have been around since the 1940s. When I was much younger, I used to buy surplus computer boards with 6 RCA 6021 subminiatures (or equivalent), IIRC mostly connected as flip-flops. They were positioned on either side of the PCB, flanked by an aluminum plate with clips on either side--three to a side. Lots of mica caps and such on the board--and really, really cheap--maybe less than a dollar apiece. There was a good reason for this--when a board went bad, it wasn't repaired, just junked and replaced with a new one. So you got 6 tubes, 5 of which might be bad.

    This was in the heyday of "Surplus Row" on South Michigan Avenue in Chicago--dark, dusty stores just chock-full of military surplus stuff. It was heaven.

    Subminiature "hearing aid" tubes (e.g. HY245) are pre-WWII, as were the 7-pin miniature tubes (e.g. 9001, 9002).

    So, no excuse for the "bigness" per se.

    One of my old bosses worked on SAGE. He said that one of the first troubleshooting techniques was to first walk down the racks, looking for any tube filaments not glowing. He mentioned that said racks were a convenient unofficial way to keep your lunch warm...

    There are still subminiature tubes being sold on eBay. They appear to be new. Obviously, a great deal of them were manufactured.

    Not as small as nuvistors, of course, but pretty small for the time. I suspect that they weren't employed in the like of the G15 and LGP30 because they were often wired right to the circuit (no socket), so not easy to field-service.

  8. #8

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    The ENIAC is really not that similar to modern architectures. It's 10 digit base 10, and fully parallel processing. Each accumulator (all the units, actually) runs at the same time as all the rest. There were ten accumulators. The best way to think of the ENIAC is to think of it as 10 adding machines with ten operators all talking to each other, with several extra tools they can use. Programming was done by setting switches and plugging patch cables: nothing at all resembling what we normally think of as programming.

    I've done quite a bit of ENIAC programming. There are some really good emulators. Each one seems to have some really big bugs though, at least, the last time I used them. It's been at least 5 years.

    The trouble with the ENIAC was that it was severely I/O bound. When they converted it to a stored program design, they eliminated the parallel processing capability, greatly reducing the processing speed. But, it didn't actually operate any slower due to the I/O bottleneck.
    Be polite and I may let you live.

  9. #9

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    Quote Originally Posted by Chuck(G) View Post
    Subminiature (T3 outline) tubes have been around since the 1940s. When I was much younger, I used to buy surplus computer boards with 6 RCA 6021 subminiatures (or equivalent), IIRC mostly connected as flip-flops. They were positioned on either side of the PCB, flanked by an aluminum plate with clips on either side--three to a side. Lots of mica caps and such on the board--and really, really cheap--maybe less than a dollar apiece. There was a good reason for this--when a board went bad, it wasn't repaired, just junked and replaced with a new one. So you got 6 tubes, 5 of which might be bad.

    This was in the heyday of "Surplus Row" on South Michigan Avenue in Chicago--dark, dusty stores just chock-full of military surplus stuff. It was heaven.

    Subminiature "hearing aid" tubes (e.g. HY245) are pre-WWII, as were the 7-pin miniature tubes (e.g. 9001, 9002).

    So, no excuse for the "bigness" per se.

    One of my old bosses worked on SAGE. He said that one of the first troubleshooting techniques was to first walk down the racks, looking for any tube filaments not glowing. He mentioned that said racks were a convenient unofficial way to keep your lunch warm...

    There are still subminiature tubes being sold on eBay. They appear to be new. Obviously, a great deal of them were manufactured.

    Not as small as nuvistors, of course, but pretty small for the time. I suspect that they weren't employed in the like of the G15 and LGP30 because they were often wired right to the circuit (no socket), so not easy to field-service.
    Those *look* to be about twice the size of the ones I have, which are about 5/16" diameter. But it's hard to tell, they may be the same size. The ones I have are Soviet manufacture. Unfortunately, I haven't seen them for twenty-five years; I may not actually own them anymore. I never knew the specs of them, but I did build a reasonable audio amplifier with one, which was a triode, using only 12V at the plate.
    Be polite and I may let you live.

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    They're small, but not as tiny as nuvistors.

    Here are some next to a 12AX7 for comparison

    Note that these are 6.3V heater-type and use round bases, unlike the tubes in portable radios (e.g. Motorola Pixie) described here

    I used the tube sockets in a junked Pixie as my first transistor sockets (think 2n109 with short leads).

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