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Bringing Back the PDP8 372

Anne Thwacks writes " Andrew Grillet has decided that the Digial PDP8 - the first ever minicomputer, will rise from the dead. He is calling it the PDQ8. Sure others have done software emulations, and even hardware clones, but he is not just building a hardware clone, but trying to revive the whole idea of 12 bit computers!"
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Bringing Back the PDP8

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  • TRS80 (Score:5, Funny)

    by ClamClit ( 546323 ) on Monday November 25, 2002 @11:17AM (#4751714)
    ...and I building a 3.5 GHz TRS80 with a GIG of RAM and 2 5 1/4" 80 GB floppys. its the cats ass
    • Re:TRS80 (Score:2, Interesting)

      by ch-chuck ( 9622 )
      DOn't laugh - IMSAI, which predates the TRS80, is soon to sell, for under $1000, a series two [] with 20Mhz Z8S180, 1 meg static memory, AND toggle switches and flashing lights! CP/M never ran so fast.
  • what for (Score:3, Insightful)

    by neotokyo ( 465238 ) on Monday November 25, 2002 @11:17AM (#4751715)
    while the geek factor may be high, what sort of 12-bit software is it going to run ? linux?
    • Re:what for (Score:3, Informative)

      by mirko ( 198274 )
      RT11, of course :-)
    • Re:what for (Score:4, Informative)

      by Detritus ( 11846 ) on Monday November 25, 2002 @11:30AM (#4751834) Homepage
      Probably OS/8, which if I remember correctly, was a multi-user operating system. You can run a multi-user system on a PDP-8 with 32KW of core.
      • Re:what for (Score:5, Funny)

        by rainwalker ( 174354 ) on Monday November 25, 2002 @11:39AM (#4751902)
        Now, I'm no expert on legacy computers, but a machine with 32KW of core sounds dangerous...suddenly my 80W Athlon looks puny!
      • Re:what for (Score:4, Informative)

        by dhogaza ( 64507 ) on Monday November 25, 2002 @12:09PM (#4752111) Homepage
        OS/8 was a single user system. I wrote a multi-user kernel that ran multiple copies of OS/8 customized to hook into device drivers supported by my kernel. It supported virtual paging using a hardware hack first suggested by Richard Lary (the author of OS/8). We ran four or five users on a 32KW 8/E with a couple of RK05 drives.

        We never distributed it because paging performance without the hardware hack was very bad (every CDF instruction needed to be trapped and mapped in software) and the hardware hack was only developed for the 8/E and piggy-backed on one of the system boards destructively (i.e. once modified your 8/E wouldn't run without our hardware).

        But it was used internally by the company I developed it for until about ten years ago.
    • Re:what for (Score:5, Funny)

      by Waffle Iron ( 339739 ) on Monday November 25, 2002 @11:40AM (#4751907)
      while the geek factor may be high, what sort of 12-bit software is it going to run ? linux?

      In the bottom of a box somewhere in my basement, I've still got the BASIC source code for the Star Trek game we used to run on our high school's PDP-8. For each player's turn, it printed out the map of the current galactic sector along with any Klingon ships on the line printer.

      It's funny, I remember when we played that game we felt like we had godlike control over a mysterious and powerful machine. Now when I play computer games, I mostly feel like a twitching moron.

    • by Anonymous Coward on Monday November 25, 2002 @11:52AM (#4751988)
      What else would be a 12-bit OS?
    • BSD might actually have ran on it. The 4.4BSD, maybe Reno or Tahoe. Heck, the 2.x BSD's might even be supported as well.

      I could of course be wrong, but I really think these PDP's ran UNIX. RT11 seems unlikely, since that was a PDP11 OS. Either some V[something] or a BSD unix ran ot it, I am almost positive.

      Please do correct me if I'm wrong of course. It's been a while, ya know :)

      • Re:what for (Score:3, Informative)

        by dhogaza ( 64507 )
        OK, you're corrected :)

        The PDP-8 never ran anything remotely resembling Unix. The very first version of Unix ran on the PDP-1/7/9/15 18-bit family (a PDP-7 IIRC). The architecture of this family was similar in many respects to the PDP-8 and indeed preceeded the PDP-5/8 family. You can think of the PDP-8 as being scaled down from the earlier family's 18 bits to 12 bits. To make it cheaper, of course.

        The original Unix-written-in-C ran on the PDP-11 (the PDP 1/7/9/15 family version was written in assembly, IIRC). The first BSD version of Unix was written for the VAX family ...
  • An idea (Score:3, Insightful)

    by AppyPappy ( 64817 ) on Monday November 25, 2002 @11:17AM (#4751719)
    An idea whose time has passed. Maybe he can build an Edsel while he is at it.
  • ENIAC (Score:3, Funny)

    by kaden ( 535652 ) on Monday November 25, 2002 @11:19AM (#4751733)
    Anyone for hitting up the local vacuum repair shop and getting started on an ENIAC reconstruction project?
  • by ekrout ( 139379 ) on Monday November 25, 2002 @11:20AM (#4751740) Journal
    Many of you probably have used Xilink's 1000, 2000, or 4000-series FPGA card during laboratories for your undergrad classes.

    Well, if you'd like, you can follow this design [] of an FGPA implementation of the original PDP-8 computer!

    If you've used Verilog (a hardware design programming language), like I have, you can even download all the code []!
  • 12 bits (Score:5, Interesting)

    by vasqzr ( 619165 ) <vasqzr.netscape@net> on Monday November 25, 2002 @11:20AM (#4751745)

    I found that, where you are not primarily handling ASCII, 12 bits was a very good size.

    Maybe someone would enlighten the rest of us on why a certain bit size is better than another, and why we currently use 8/16/32/64, instead of 12/24/48/96 ?
    • Re:12 bits (Score:5, Interesting)

      by FauxPasIII ( 75900 ) on Monday November 25, 2002 @11:25AM (#4751788)
      >> Maybe someone would enlighten the rest of us on why a certain bit size is better than another,
      >> and why we currently use 8/16/32/64, instead of 12/24/48/96 ?

      Because powers of 2 are easier to work with in binary.
      • I don't think there's any fundamental DISadvantage to using 12,24,36 and 48 bit words and addresses. The question is not whether the memory addresses will be in terms of some power of two (of course they will), but whether the sizes of words used to hold values and addresses should likewise be an even power of two. Even numbers, surely, but not necessarily a power of two bits wide.

        At the time when things pretty much fell into the currently accepted pattern, word sizes that were even powers of two happened to be convenient:

        2^8: enough to hold the complete latin alphabet
        2^16: Enough bits to handle the entire address space of a 1980s microcomputer
        2^32: Enough to handle almost any day to day integer calculation

        It's like the inch-foot-yard-furlong-mile of English measurements. These are well suited to the kind of day-to-day measurements that people make, as inconvenient as they are for calculation. Eight, sixteen and thirty two bit words and addresses were big enough in the 1980s, but not so big as to be wasteful.

        It's interesting to speculate how things might have been different had the industry settled on twelve and twenty four bit word sizes. It may have been more convenient for people with non-latin alphabets, although not as commodious as a sixteen bit per charcter system. And a lot of effort was wasted in the nineties with the limitations of sixteen bits address spaces (the segmented memory architecture, near and far pointers etc). The need for a larger flat, memory space might have been staved off for several years until 16MB chunks were too small.

        I don't know if that's a good thing or bad thing. We might be struggling with a 24-48 bit conversion today instead of happily using our P4s and Athlons and waiting for the high end users to hash out the 32-64 bit conversion.

    • Re:12 bits (Score:3, Interesting)

      8 bit is base 2

      1 2 4 8 16 32 64 128 256 512

      So I suppose 12 could be ....

      1 3 6 12 24 .... hmmmmm..... now quite correct

      1 2 3 6 12 24 ... 60 ... 420


      12 is good because
      12/6 = 2
      12/4 = 3
      12/3 = 4
      12/2 = 6
    • Re:12 bits (Score:2, Informative)

      by Viol8 ( 599362 )
      7 bits was used when the ASCII character set was initially devised (though 4 bit had been used before that) with the 8th bit being used for parity checks. At some point someone decided to hell with parity checks , lets use the 8th bit to double the number of characters available. And once 8 bit became standard in hardware then 16 bit narually followed as you could still divide a 16 bit word in 2 to get 8 bit characters. Similarly with 32 bit you can divide a 32 bit word to give two 16 bit words and hence can run 16 bit software on 32 bit hardware with a bit of help. Thats the gist of it anyway.
      • Character Codes (Score:3, Informative)

        by Detritus ( 11846 )
        6-bit character codes were popular before the introduction of ASCII (7-bit) and EBCDIC (8-bit). The PDP-10 had a 36-bit word, which could hold 6 6-bit characters. It also supported other character codes, such as ASCII.

        If you look at old assemblers and compilers, the limit on the length of a symbol/variable name is often the number of characters that could be squeezed into a single machine word.

    • "Base 8 is just like base 10 really. . .if you're missing 2 fingers."

      • ...well, you could just omit using your thumbs...but that wouldn't be as masochistic (tango-y goodness!)...

        Tom L. has always been a Haavaadite, not from MIT, as in the "Harvard Fight Song," and the lines, "These are the only ones of which the news has come to Haavaad/And there may be many others, but they haven't been discovaad." (Rhotic-lossy dialects bother me, since I speak one of the few English dialects that's fully rhotic.) I imagine it matters to some people (probably they go to Harvard).

        Also, as far as I know, he's still there, although long since an Emeritus.
      • Wow, 10 fingers, how many thumbs do you have?
    • Re:12 bits (Score:5, Informative)

      by sql*kitten ( 1359 ) on Monday November 25, 2002 @12:14PM (#4752151)
      Maybe someone would enlighten the rest of us on why a certain bit size is better than another, and why we currently use 8/16/32/64, instead of 12/24/48/96 ?

      This article [] explains why base-3 systems are actually a lot better than base-2 from a theoretical perspective, but that it was much easier to design hardware in base-2, so base-2 became the de-facto standard. Nowadays we could probably fab base-3 hardware fairly easily, but it's not worth doing so with all the base-2 hardware already in existance.

      As for 16/32/64 instead of 12/24/48, it's just one of those things. IBM's earlier AS/400s ran on 48-bit processors (now they are 64-bit). 96-bit floating point is an IEEE standard. And do you know why file permissions in Unix are rwxrwxrwx? It's because they borrowed that idea from another operating system designed for 9-bit bytes and a 36-bit processor.
      • by Anonymous Coward on Monday November 25, 2002 @01:20PM (#4752626)
        As nice as a base-3 system my be in theory, there are very good reasons for sticking to a base-2 system in hardware. As we are moving to smaller and smaller fabrication processes, it is necessary to lower the supply voltage Vdd. For example, now that we are approaching the 0.1um and 900nm levels (at least in research labs), Vdd is getting down around 1 Volt. However, the Vt (the threshold voltage needed to turn "on" a MOS transistor) stays the same, because it is determined by physical properties of silicon (mostly). That means we're losing headroom. To implement ternary logic, we would need 3 different voltage levels. We're simply running out of room to do things like that. You need to leave a noise margin around your "1" and "0" values for reliable operation. (For example, if Vdd=1V, you might consider 0.0-0.4 = "0", 0.6-1.0 = "1". Then a logic gate that "sees" 0.0-0.5 interprets it as "0", etc. If you had a "0" that was really 0.4V, you would hope that "noise" wouldn't bump it up above 0.5V, or else it would look like a "1".)

        The threshold voltage for transistors is somewhere under 0.2-0.3V usually (depening on the technology & lots of other parameters). So, you absolutely need a 0.6V supply. (0-0.3 = "0", 0.3-0.6 = "1".) Unfortunately, even with Vdd=1V, you'll get voltage drops happening throughout the chip ("IR drops" - as in I=current times R=resistance) so that the 1V may only look like 0.8V to some parts of your circuit.

        From the above discussion, it should be obvious that there really isn't room to shoehorn in a third voltage level. Also, a nice feature of CMOS design is that when a gate is sitting in a "0" or a "1" state, it is drawing no (well, negligible) power. Power is only dissipated while a value is switching from a 0/1 or vice versa. Off hand, I can't think of a way to do that with a third logic-value. Consider drawing even a tiny amount of current while a gate is sitting at logic "2" (or whatever you want to call the 3rd value). 1mA (milliAmp) times 1 million transistors on a chip = 1000 Amps. That chip's going to get a little hot!

        Ok, so you've probably got at least two questions, which I will try to answer in advance. If you've got other questions - I'll just let someone else tackle those.
        Q1) Why don't we just use a higher Vdd (supply voltage)?
        A1) If you're using smaller transistor widths, you simply can't. When you use a really thin gate (i.e. 0.1um) on a transistor, the breakdown voltage of the gate is reduced. If you use a higher voltage, the transistor melts. (You could use larger transistors, but that kind of defeats the whole purpose! We make transistors smaller because we can fit more on a chip, and they operate faster and use less power.)

        Q2) Can't we lower the threshold voltage?
        A2) Yes, to some extent. (It's not always easy.) But we don't want to. Even when a transistor is "off", there is still a very small amount of leakage current flowing through it. If you reduce the Vth, you also increase the amount of leakage current. In older technologies, this hasn't been much of a problem, because the leakage current was so small in comparison to the dynamic power consumption. But as we are putting more and more transistors on a chip, the leakage power consumption in modern chips can easily add up to 30%-40% of the total power consumption. There's also another reason. If you did that, you would be lowering your noise margin. And you don't really have much control over the noise (which is why it's called that). If you reduce noise margins too much, you'll find it almost impossible to create a circuit that actually functions reliably.

        Well, I hope that satisfies some of you (and doesn't get the rest of you too upset). VLSI circuit fabrication is a really neat field. Some of the tricks that are being used these days to fabricate that chip sitting in your computer and get it running at 2GHz (or aren't they up to 3GHz now?) are quite amazing - they're doing their best to cheat physics! Using a ternary counting system to build computers may have a lot of nice theoretical properties, but I can't see it displacing binary any time soon, except possibly in some really specialized applications. (There are always exceptions.)

        That's my $0.03 worth. (Hey, I typed a lot. I think that's worth at least $0.01 extra. Maybe $0.025?.) Any errors in the above are mine, but I won't admit it.
        • by pjrc ( 134994 ) <> on Monday November 25, 2002 @03:03PM (#4753341) Homepage Journal
          Off hand, I can't think of a way to do that with a third logic-value. Consider drawing even a tiny amount of current while a gate is sitting at logic "2" (or whatever you want to call the 3rd value).

          It could be accomplished (fully static CMOS, no steady state current to maintain a 3rd logic level) with a second power supply, and circuitry designed to connect the output to either Vss, Vdd or Vmm (m for middle, for lack of any other name.. hmm) Brian Hayes's flawed assumption [] is that circuit complexity increases linearily with the number of logic levels. He writes "An obvious strategy is to minimize the product of these two quantities", refering to the radix and number of symbols to represent a number... but he just pulled that out of a hat. The required circuit complexity is not linear function of the radix, and a realistic model would quickly prove that binary is the most efficient. A fully static ternary output requires a minimum of four transistors, whereas binary requires only two.

          That chip's going to get a little hot!

          With a static CMOS circuit designed this way, power consumption would be approx 0.5 * C * f * V^2 (as it is in normal binary circuit). C will probably increase somewhat, as nearly twice as many transitors would be needed per circuit, yet fewer trits are needed that bits for the representing the same numerical range, so the increase in C probably wouldn't be by a factor of two. Presumably f (the clock frequency) would stay the same (well... I'll get to that...), and V stays the same (50% of transitions in binary are full supply voltage, in ternary 33% are full voltage and 33% are half voltage). Power comsumption would probably be similar.

          Saddly, f probably won't stay the same. C gets larger on each signal, and when driving to half voltages, the transistors that would connect to the Vmm supply get only half the effective gate voltage applied. So doubling the load and cutting the drive significantly is really going to hurt the circuit's speed.

          Dynamic logic tricks (pre-charged busses) and bicmos circuits add another interesting dimension that's too complex to worry about, though it'd be important for any microprocessor.

          But power consumption isn't likely to be a problem.

          Getting back to the old PDP-8, as I recall it was a binary machine. The motivation behind 12 bits was that 6 bits was ideal to represent both upper and lower case characters and plenty of symbols, and 12 bits (two chars) was plenty for useful math. I don't recall the popularity of 6/12 bit systems having anything to do with base-3 signaling.

    • The PDP-8 had a long life as the Decmate word processor, the 12 bit word did very well, as it could handle text, with bold, underline, etc directly.

      The 3rd party service man at a VAX site I worked at in the early 90's had a PDP-8 (W/ RK05's!) still under contract in a big milling machine at a local heavy manufacturor.
    • If you are using Ascii, the 8-bit bytes are a good size. Of course, you really only need 7 bits, but no programmer is going to like that. Then you add the concept of byte addressable word space, so you use the byte address to address doublebytes (short) and quadbytes(longs).

      As to why 12 bits is good: simply 8 bits is a bit small for an awful lot of cases, so if you use an 8-bit fundamental word length, you are often into doubleword operations. Practically, a 12 bit word length, values +/2048 or 0-4095, seems to work out useful in a lot oc control applications. When the extra bits were expensive, the saving between 12 and 16 is relevant.

      First machine I worked on was 18 bits - all 8K words of it. Enough to run a very simple Fortran compiler. From paper tape, naturally.

    • Re:12 bits (Score:2, Interesting)

      by lobsterGun ( 415085 )
      This is a story that a wisened old timer told me at a convention (the guy had a whit bushy beard so you know it has to be true).

      Back in the day there were two schools of thought: the 8 bit byte and the 9 bit byte. The 9 bit byte school represented the same data as the 8 bit byte school (0 to ff), and used the extra bit for parity.

      8 bit bytes led to 16 bit words etc...
      9 bit bytes led to 18 bit words etc...

      My reaction to the old time was to ask WTH would anyone do this?

      His response was to go into a discussion of 36 bit computing. "Ya see son. When you have 32 bits you can divide those bits evenly 6 ways:
      32 single bits,
      16 2-bit groups,
      8 4-bit groups,
      4 8-bit groups,
      2 16-bit groups,
      1 32-bit group.

      With a 36 bit system you can divide those bits evenly 9 ways
      36 single bits
      18 2-bit groups
      12 3-bit groups
      9 4-bit groups
      6 6-bit groups
      4 9-bit groups
      3 12-bit groups
      2 18-bit groups
      1 36 bit group

      using 36 bits give you more flexibility in addressing."

      He went on to tell be stories about how they explioted the advantages of 36 bit computing back when he had worked at Compuserve and how sad he was that 36 bit systems had died.

      It could very well be that 3 12-bit bytes are used to make up a 36 bit word... ...or it could be that that old timer was full of crap or off his meds or something. The world may never know (Much like the number of licks it takes to get to the center of a tootsie pop).
  • by solostring ( 620535 ) on Monday November 25, 2002 @11:20AM (#4751747) Homepage
    I fondly remember the PDP8. My father had one installed in the garage when I was a kid, and had my first experience of programming on it when I was 8 or so.

    On the subject of PDP8's, I was surprised to hear that they were used in communications in Hong Kong up until at least 1999 for a number of financial institutions. I worked with an old computer technician who earned a fortune maintaining these beasts. I wonder if they are still being used in HK after the Chinese reclaimation?.....
    • I was surprised to hear that they were used in communications in Hong Kong up until at least 1999
      I wonder if they are still being used in HK after the Chinese reclaimation?

      Possession of Hong Kong went back to mainland China in 1997, so I would say yes, they were in use for at least two years after the changeover. (I don't know if they are still in use, though.)
  • Apparantly, the PDQ8 doesn't withstand the /. effect very well. And of course, obBeowulf.
  • Why? (Score:5, Interesting)

    by BWJones ( 18351 ) on Monday November 25, 2002 @11:23AM (#4751772) Homepage Journal
    but he is not just building a hardware clone, but trying to revive the whole idea of 12 bit computers!"

    So, after reading the article, I am still trying to figure out....Why revive the idea of 12 bit computers? Other than nostalgia (which is why people still drive Studebakers, old Ferraris and old Porsche's I suppose), what is the point?

    • Re:Why? (Score:5, Funny)

      by Kibo ( 256105 ) <naw#gmail@com> on Monday November 25, 2002 @11:37AM (#4751887) Homepage
      I can't be sure about Studebakers but in the case of classic Ferraris and Porsche's I'm fairly certain the idea is still to get laid.
      • Having owned a classic (1973) Porsche 911t Targa, and currently owning a 1975 Corvette Stingray T-top, I can tell the idea is somewhere between getting laid, and the sheer fun of a classic performance car.

        Some people, (myself obviously included) think that the pre-gas shortage cars in the US were much better looking cars. The current models seem to still be recovering from the 80's and 90's ideas of "Box on Wheels" and "Wind Tunnel Styling". I wouldn't own a new Porsche.

        I think the idea with the PDP however, is not nostalgia. It was (and is) a very stable platform. Many companies either just left them, or are still using them. We just left the VAX platform not too long ago, despite having used Alphas concurrently for ages.

        After all, if it works, why upgrade?


      • Re:Why? (Score:4, Funny)

        by image ( 13487 ) on Monday November 25, 2002 @12:25PM (#4752258) Homepage
        > I can't be sure about Studebakers but in the case of classic Ferraris and Porsche's I'm fairly certain the idea is still to get laid.

        I'm rather sure it is easier to get laid in a vintage Studebaker [] than a Ferrari [].

        More leg room and all.
    • which is why people still drive Studebakers, old Ferraris and old Porsche's I suppose

      People care about even stranger things than that. Just yesterday, I saw a group of Edsel fans driving their cars in the Doodah Parade []. When I thought that was goofy enough, the people standing next to me pulled out their pictures from a trip to a Corvair fan get together (The Great Western Fan Belt Toss & Swap Meet []). ISTR that there are even Trabant fan clubs, of all things. Name a piece of obsolete technology, and there's a good chance that some people will be fanatically devoted to it.

  • by Anonymous Coward on Monday November 25, 2002 @11:24AM (#4751777)
    Whew! I hope he puts it somewhere on the internet. I've been looking for a place to hide my super Swordfish-style decryption software before I go to prison...
  • Paper Tape Reader! (Score:2, Interesting)

    by Anonymous Coward
    I hope you kids realize that the primary way to feed data into this machine was via an ASR-33 teletype style console that punched a paper tape. The PDP-8 had a paper tape reader which then read the punched tape.

    None of those airy-fairy magnetic tape drives in those days on a machine like that! The front panel switches were might handy too for such esoteric operations such as booting the thing.
  • by trash eighty ( 457611 ) on Monday November 25, 2002 @11:25AM (#4751796) Homepage
    people have been building replicas of old cars, boats and aeroplanes for years. i suppose its logical that people would start building replicas of old computers sooner or later. much computer hardware is boring these days, generic MBs and computers. ahh the good old days when we had some variety ;)

    all power to him!
  • Interesting (Score:3, Insightful)

    by GeckoFood ( 585211 ) <geckofood AT gmail DOT com> on Monday November 25, 2002 @11:26AM (#4751797) Journal

    It would be fun to play around with something cool like that, just for the sheer ability to say "Hey, y'all watch this!" (Oops, better watch that there accent, ya rekcon?) It would especially nice to have a C compiler or something to develop apps for it, again just for the coolness factor.

    With a twelve-bit computer, what is the address space, anyway? Something like 2048 words? Suprisingly, you can actually do a lot with that if you code it tightly. No, can't do weather map rendering too well or anything like that, but I bet you could pull off a stripped down version of NetHack or something...

    Coolness, regardless. :-)

    • The PDP-8 had a 4K (4096x12) address space.

      Somewhere I have an old DEC PDP-8 handbook. They released a native FORTRAN compiler for the PDP-8. It just shows what you can do with clever coding and lots of overlays.

    • Bad omen. Here in the South, "hey y'all, watch this!" are often the last words you hear.
    • C compiler indeed.The PDP-8 was natively a FORTRAN machine. Apps can be developed perfectly well in FORTRAN. . . and the coolness factor is higher.

      King Arthur: Noble FORTRAN compiler, although you are a dead language. . .

      FORTRAN compiler: I'm not dead yet sire.

      King Arthur: Although you are a mortally wounded language. . .

      FORTRAN compiler: Actually sire I'm feeling a bit of all right.

      Again, C compiler indeed. Gag my PDP-8 with a spoon. ( Actually, that would be 'anatomically' possible)

      Here's an interesting little page on the history of the PDP-8 OS's and languages:

      And here's an interesting computer history page with several FORTRAN links ( as well as UNIX and C links): se um.html

      C compiler. . . phbbbbbt!

  • by ekrout ( 139379 ) on Monday November 25, 2002 @11:26AM (#4751800) Journal
    Well, I found this [] old link in my bookmark manager. It details the history of EMS (sound studio) in vivid detail, including a listing of all their original equipment.

    The interesting part is that they posted high resolution images of their setup, which includes PDP-8 microcomputers!

    The image: []
    The PDP-8s:
    Left side - Teletype for PDP8
    Left bay - PDP8/L Computer ("Leo") 4K x 12 bits (=6K bytes) 1.3 s cycle (0.77MHz), 32K Hard Disk Store
    Center left bay - PDP8/S Computer
  • by MosesJones ( 55544 ) on Monday November 25, 2002 @11:28AM (#4751818) Homepage
    12 bit is much better for patriotic Americans.

    Think on it, power of two is a far to simplistic and dare I say it European system for the patriotic American. In Europe they use metres, kilometers, grams and kilgrams. All this regulation of structure around a number like 10 is typical of Europeans. Americans use sensible systems like 14 pounds (abbreviated sensibly to lbs as pounds clearly contains the letter l) to a Stone and 16 Ounces (again with a sensible abbreviation of oz) to a pound. Who needs these ridiculous regimented European systems that dicate that everything must follow a sensible pattern?

    Patriotic Americans arise. 12 bits to a byte, 7 bytes to a word, 13 words to a sentence and 1764 bits to a chain.
    • no, 12 bit is best for the BRITISH patriot. Bring back the good old imperial measurements...It's only the EU making us use the french system.
      Why do you think the americans use imperial?
      Because we used it first.
    • You know, I have never, in 43 years, heard an American use "stone". That's a Brit thing.

      And of course we inherited the whole system. As I recall, the "lb." abbreviation has something to do with the French "livre", and also led to the the "pound sterling" symbol, that fancy-schmancy "L" that featured so prominently on the Commodore keyboards of yore.

      As for word width, well, there's nothing especially holy about multiples of 8. CDC used to make machines with a 60-bit word, because they mostly dealt with numbers, not text manipulation, and big fat words like that allow for big fat numbers, although storing an ASCII file in 60 bit words would be clumsy as hell (As a side note, I used to work with the CP1600, which was a real 16-bit machine. There was no way to address a byte, although there was an 8-bit shift so that you could pack ASCII into words to save space and slow down annoyingly fast programs.)

      • And of course we inherited the whole system. As I recall, the "lb." abbreviation has something to do with the French "livre", and also led to the the "pound sterling" symbol

        Which is interesting because the word Sterling comes from starling, which meant "small star" in mediaeval English - it was the symbol on the coin for the unit of currency. So the currency symbol should probably really be a *.

        Lb is from "livre" (French for pound) and dollar comes from "taler", an old German currency.
        • and "taler" comes from the town of Joachimsthal, where the silver was mined.
    • I must respectfully disagree.

      While a measurement system based on powers of 2 seems fairly straightforward and intuitive to your average techno-nerd, it is still incomprehensible to the average Patriotic American. In fact, I would venture to say that 1024 bytes in a kilobyte is every bit as opaque as our beloved, patriotic, English units.

  • What Gives? (Score:4, Funny)

    by SuperDuG ( 134989 ) <<kt.celce> <ta> <eb>> on Monday November 25, 2002 @11:32AM (#4751855) Homepage Journal
    Everyone is waiting around for 64-bit chips to hit the home computer market at resonable prices, is this some kind of protest "bits, we don't need no stinkin bits".

    On a related note, I'm going to be designing my own 32 bit system. It's going to be pretty cool having an asthetically pleasing case, and run most all of the common software out there, but make the operating system run on top of bsd. Then I'll make really high-end systems, and education type systems, and laptops.

    Now I'm 95% of the way done with this whole project so I've hired an advertising firm to come up with some commercials. I figure I'll show joe average sixpack switching from the normal x86 windows machine, to my machine, I'll call them 'Switch-Ads'.

    My proprietary systems will never run on anything else, and you will be forced^H^H^H^H^H^H encouraged to only buy via our website.

    I'll call them MOC's ... and the company will be named Orange.

  • What for? (Score:3, Funny)

    by archeopterix ( 594938 ) on Monday November 25, 2002 @11:32AM (#4751860) Journal
    8 bits should be enough for everyone.
  • From: []

    "My mother was a Fortran programmer using computers that looked like this [picture of an ancient IBM 608-series supercomputer]"
  • Text based games (Score:5, Interesting)

    by Technician ( 215283 ) on Monday November 25, 2002 @11:36AM (#4751883)
    I remember playing the father of the Zork series of games on a PDP 11/35 which was the newer 16 bit machine. The game was called Adventure. We got the game on a 5 Meg 14 inch hard drive (RK05) and wasted a bunch of paper making moves on a keyboard/printer terminal. The scrollback feature of the hardcopy was great for finding your way out of a maze again. Adventure has since been ported to CPM and DOS. The game is still a great game and will challenge the thought process. Take a pencil and paper to keep from getting lost. There is no map. Do a google search to find this true classic game. You should be able to run it in a DOS window on Windows 95 before DOS and Windows 95 expire at the end of this year. I'm still trying to figure out who the shadowy figure is who tries to get my attention.
    • XYZZY (Score:4, Funny)

      by MosesJones ( 55544 ) on Monday November 25, 2002 @11:53AM (#4751994) Homepage

      And of course

      "with your bare hands?"
      you stand amazed as the dragon lies dead at your feet.

      Bugger graphics you can't beat a maze of twisty passages, all different.... or was it a twisty maze of different passages.
    • Only official support for them will. DOS will never 'expire.' It's done. Of course you can't buy MS-DOS anymore, but there's always DR-DOS and FreeD0S, both still supported.

      W95/98, on the other hand, will actually expire some years in the future. I discovered this on a reinstall that went bad. Windows simply refused to install. Having a Gateway at the time I called tech support and the issue was tracked down to a buggy BIOS (gotta watch for those updates) that had reset my system clock to a future time.

      "Ah, there's your problem. Windows has a 30 year time bomb built in so it thinks it's expired."

      Ummmmmm, good to know. I guess that's how long we've got to port all our favorite W95/98 games to Linux ( or maybe Plan 9).

  • by MarkWatson ( 189759 ) on Monday November 25, 2002 @11:40AM (#4751912) Homepage
    But, it was just an Intersil Intercept Jr. single board version of a PDP - same instruction set though.

    It was fairly easy to program for - I wrote a simple cross-assembler on a Dec-10 that would print out my assembler source with machine code (in octal). For short programs, it was fairly quick to enter the programs in octal. Since the Intercept Jr. was all CMOS, the programs would stay in memory as long as I wanted without runnng down the batteries.

    Really, it was very cool, and fun.


  • What a memory... (Score:2, Interesting)

    by NormHome ( 99305 )
    We had one of these in high school (25 years ago), looking back I thought it was pretty cool but man that single DEC tape drive was a royal pain. We also had an old teletype with a paper tape punch, haven't seen one of those since. In my junior year we got a grant from the state and got a PDP-11 with dual 8 inch single sided floppies, now that was living!
  • I just dont see the point of resurrecting 12-bit hardware when we have 64-bit now. Why the nostaglia? PDP is dead! the world will never see another 12-bit. Is this guy a museum curator?
    • why disdain the past? Who knows, maybe your grandma knew something about sucking eggs that you don't.

      If nothing else the guy is obviously having fun. Believe it or not when you get to be Eleventy years old your own hobby just might turn out to be keeping 16 bit Intel stuff alive.

      I mean like, why ride skateboards when we have bicycles now? Why, because you *want* to.

  • by GreyPoopon ( 411036 ) <> on Monday November 25, 2002 @11:46AM (#4751949)
    I remember seeing one of these puppies when I was in high school. It was no longer in service, but still had most of its internal components. In fact, I still have one of the "flip chips" that I took from inside it. Anyway, I believe I recall a dial on the front of the main panel that allowed you to choose the word size. I can't remember whether 12 bits was the minimum or the maximum, though. Can anybody verify that this existed, or am I just remembering some strange dream?
  • How can they possibly expect us to use the efficient new Radix-50 character encoding to store text? RAD-50 requires 16 bits to compact characters.

    DeCastro was right, this 12 bit nonsense will never go anywhere.
  • by randomErr ( 172078 ) <ervin,kosch&gmail,com> on Monday November 25, 2002 @11:48AM (#4751966) Homepage Journal
    Some mentioned earlier on this [] thread jokingly about making a super fast computer based on old architecture.

    Has anyone actually done that? Has anyone actually taken say, a Tandy Color Computer 3's hardware and boosted it up to something approaching our current standards? I'm not talking emulation on a x86 platform. I mean fully working with a processor with a native OS.

    Those architecture are so simple, with kernels so small you could print the hex binary out on a couple of pages. Imaging how fast an accounting package would be on a 1 gHz, or even a 200 mHz.

    I know this maybe off topic, but if someone could resurrect a 12-bit system to a more modern standard, why not other system. DOS [] is still viable [] in certain circumstances, why not these platforms.

    Think about an 8-bit controller with a serial connection, flash memory, and a RCA video out jack that is based on a C64. There is a TON of documentation for programming on something like that. Linux guruâ(TM)s could use C/C++ and Windows users could use Commodore BASIC.

    Oh well thatâ(TM)s just my ramblings.
    • I used to work for a UK supermarket in the Cash Office, and the PC that ran all the Checkouts and the SSM system (stock management) was a lowley 486-66 pc with 48mb ram, and it crawled. It took 4 hours to do a standard end-of-week data compile. It ran some wierd IBM Dos OS, and used green screens etc.

      Then one day they replaced it with a PIII700 system, 128mb ram the works. Still ran this IBM Dos OS, but the end of week took seconds. Literally, we could no longer get away with a 4 hour break!

      The same supermarket is still using this Dos OS on p4s now, so i wonder what the speed is like now.
    • the upgraded CoCo was called. . . a Mac. You can still buy 6800 series chips, although you have to hunt around a bit. They're still very usful for a lot of things.

      On the other hand the venerable Z80 not only has never gone out of production but is being updated just as you suggest: C: z80+chips&hl=en&ie=UTF-8

      There are an awful lot of uses for small, fast, cool running, general purpose and cheap as penny candy chips.

      "Charles Luther" in "Runaway" understood this full well when he used 8088's to power his nefarious robotic killing machines.

  • Not Bad for its day (Score:2, Informative)

    by Anonymous Coward
    The PDP-8 wasn't bad for it's day. They even had a Time Sharing System that ran on it that gave each user a whopping 4 K of space do do whatever they wanted to do with it. It supported up to 16 simultaneous users. I know, I'm old enough to have gone to a college with one of those beasts as a shiny new grant from DEC. We had 2 high schools and one private school hoked up to us by the old 110 Baud ASR-33 teletypes. It was a hoot trying to make anything run on it. Assembler was about your only choice as Basic didn't have any file I/O until about 1973 - 1974.

    Why bring it back? Why not? It may not ever be used for much, however who says all the cool computers have to be uber-machines? This next comment isn't meant to start a flame war, but I'd like to see some of today's bloatware folks try and make a program of any substance work on one of those puppies. I've seen some code from folks used to huge addressable and virtual memories and YIKES !

  • You know, I work with PDP11's day in and day out. DEC's last PDP processor was, I believe, a PDP 11/93. It has a whopping 2 MB of RAM and 8 serial ports on the processor board! This was a double sized board only taking up 2 slots on the DEC backplane that took the function of 5 boards that took up 5 slots each. Of course the disk controller, clock card and other boards are separate. These boards are circa 1990. They are in a custom digital dictation system that can handle 64 simultaneous audio ports where people are either dictating or transcribing. The OS is the roll off your tounge: RSX11M+. These systems, which we are replacing slowly but surely, have been absolute work horses lasting for at least 10 years.

    I jsut had to reboot one this morning... :)

  • by Bruce Perens ( 3872 ) <> on Monday November 25, 2002 @11:57AM (#4752020) Homepage Journal
    If you want to program old microcomputer architectures, learn the PIC microcontroller, which is based on some Control Data Co. Peripheral and Input Controller (I may have the "I" wrong in that acronym). It's available in 12, 14, and 16-bit flavors. It doesn't have much of a stack. And it has the virtue that, as a $1 microprocessor, it's still practical for many projects, while a PDP-8 is really an intellectual exercise at this point.


  • by Tsali ( 594389 ) on Monday November 25, 2002 @12:02PM (#4752059)
    a rough quote from Monty Python...

    "I built the castle in the swamp. They said it would fall over but I did it anyways. Sure enough, it did. I build a second castle and that one fell into the swamp as well. But the third castle stayed."

    Looks like he needs another iteration.
    • Less rough, though still offtopic quote:

      When I first came here, this was all swamp. Everyone said I was daft to build a castle on a swamp, but I built it all the same, just to show them. It sank into the swamp. So I built a second one. And that one sank into the swamp. So I built a third. That burned down, fell over, and then sank into the swamp. But the fourth one stayed up. And that's what you're going to get, Son, the strongest castle in all of England!

      (No longer to-the-word-)But I just want to sing: ... And no singing!

  • by Ella the Cat ( 133841 ) on Monday November 25, 2002 @12:04PM (#4752077) Homepage Journal

    I'm old enough to have done an electronics project building a joystick interface for a PDP8 as an undergraduate. I spent ages soldering TTL chips and after a few weeks plugged the card in, to a strong smell of fish and burning insulation. It wasn't my fault, the slot in the edge connector was too wide, and every single connector on the backplane had shorted to every other. It was 6 months to get the machine repaired, so someone figured out they could take out the power transformer, scrape off the burnt mess, figure out how many primary and secondary turns were needed on the transformer, then wind them on using a reel of wire and a lathe. They go the machine going, someone else filled the board slot with epoxy and cut a new slot. My project was saved! A few weeks later i reached round the back of a PDP8 to unplug a power connector, grabbed the live pin, but was saved because my arm was earthed to the PDP8 case. I love that machine, I still have the instruction set on a sheet of paper.

  • by ch-chuck ( 9622 ) on Monday November 25, 2002 @12:04PM (#4752078) Homepage
    run your very own pdp8, pdp11 or even an Altair with disk basic or cp/m - here []. I've recently completed some serious z80 assy projects using simh on my Linux notebook. Works great w/o having to mess w/ flaky hw.

  • by dpbsmith ( 263124 ) on Monday November 25, 2002 @12:09PM (#4752106) Homepage
    Until I actually started programming a PDP-8 (in assembly language, of course), I would never have believed that you could program comfortably in such a seemingly restricted instruction set. And, conversely, when I moved to a PDP-11, I thought I was going to revel in the freedom and power of all those instructions, all those registers, those addressing modes, those index registers... and the ability to access 65536 bytes directly.

    If C is "high-level assembly language," then the PDP-11 is "a computer that directly implements C."

    To my surprise, though, I didn't really find that a lot was gained. Programming a PDP-11 didn't really FEEL much easier or more powerful than programming a PDP-8. And it was amazing how much every program expanded in size. It's been said that the PDP-8 instruction set was the most core-efficient ever devised, and I'd believe that.

    On the other hand, when I tried programming a 6502, which on the face of it doesn't SEEM that much more restricted than a PDP-8, I just about went bananas.

    Having said all that, I'm still not sure I see the point. The sweet design for a computer has to depend on the economics of the hardware around it. Who cares? Even IF the "core-efficiency" thing were true, and even IF you could use standard RAM with a 12-bit processor and not waste any bits, and even IF it turned out that the PDP-8 design were, say, 30% faster and used 30% less RAM for a given program than x86... how could it matter?

    If the Alpha, which really WAS a superior design, wasn't superior enough to overcome Intel marketing, customer inertia, and only the normal amount of mismanagement, how can a PDP-8 be anything more than a curiosity?
    • by dhogaza ( 64507 ) on Monday November 25, 2002 @12:29PM (#4752304) Homepage
      If C is "high-level assembly language," then the PDP-11 is "a computer that directly implements C."

      Actually it's fair to say that C was developed as a "high level assembly language" for the PDP-11, in other words you've got it slightly backwards. The postfix "++" and prefix "--" operators correspond to the PDP-11's autoindexing mode and when applied to a dereferenced pointer map directly to "(Rn)++" (once the pointer's been moved to a register.

      I doubt C would have these constructs if the PDP-11 didn't provide the corresponding register mode.

      As far as the PDP-8 being perhaps the most core-efficient design ever, speaking as someone who once developed system software for the PDP-8 and afterwards compilers for the PDP-11, yes, I'd say you're right.

      As long as you could fit program and data into 4096 12 bits words, that is. If your program could fit into 4096 12 bit words accessing data in the remaining 28KW was relatively easy due to the semantics of the CDF instruction. But once your code itself outgrew the first 4096 words things got bad in a hurry, because cross-bank subroutine calls using the CIF instruction were fairly expensive.

      Gordon Bell designed both the PDP-8 and the PDP-11, and they were designed with different goals in mind. The PDP-8 was designed to be programmed in assembly code - the page and memory bank addressing structure made the development of efficient compilers impossible (it's not an accident that no system programming language like C was never implemented for the PDP-8 architecture).

      The PDP-11, on the other hand, was the first minicomputer designed with the compiler writer in mind. The instruction set was very easy to generate code for, much easier than for many mainframe machines that in those days still often had a single accumulator and some auxillary special-purpose registers. The PDP-11's clean, general-purpose register design and (relatively) orthogonal instruction set made compiler writers like myself almost faint in anticipitory pleasure when the design was first announced.

      While Gordon Bell designed the PDP-8 and PDP-11, the original engineering plans for the PDP-8 are signed by DeCastro, who did the implementation. He submitted a rival design for DEC's 16 bit minicomputer that was no where near as clean or compiler-writer-friendly as Bell's PDP-11 design.

      When the PDP-11 design was chosen, DeCastro left and started Data General, and his 16-bit design became the oft-loathed Nova.

      CDC's 12-bit PIC design was much inferior to the PDP-8's, IMO ... the PDP-8 still serves as a great example of minimalist design in an era where each bit of the accumulator was implemented by a double-width card (each BIT, thirteen of these cards in all, 12 for the accumulator bits and one for the overflow LINK bit).
  • Sounds cool, and reminds me of a project I've been tinkering with for about a year now -- a multiprocessor system based on the 6502 (actually, the 65c02), the same chip as was in the Apple II, Atari, the C64, and the original NES, among others. Problem is, my electronics knowledge at this point is not good enough to get beyond a good theoretical knowledge of what would be involved, though my 6502 assembly language skills are still sharp enough to write the firmware and software.

    I only mention this because I hope someone who does have the requisite electronics skills will email me so we can join forces.

    As for the earlier post to the effect of "what is it good for?", I can only say that it's fun to do, and old computers are good for the same things they were good for when they were new. One may as well ask what a 1965 Mustang is good for.
  • That was the PDP-1, released in 1960, 5 years earlier.

    The PDP-8's distinction was to be the first mass-produced minicomputer.
  • The Harris HD-6120 "PDP-8 on a chip" is still available, and is what this guy is using: 2. htm

    The only point I could see in using FPGAs would be if you were trying to rectreate an early MSI PDP-8 (these things existed before the single-chip microprocessor).
  • by panurge ( 573432 ) on Monday November 25, 2002 @01:57PM (#4752822)
    This is so long ago I can't even remember the manufacturer, but there were at least 2 CMOS implementations of a PDP-8 processor. Has anybody observed that the instructions were based around core memory, so the accumulator was cleared when it did a store? If you could get the core again, a home computer with a PDP-8 processor and core memory would really benefit from a modbox with windows and lights.

    For some industrial control jobs, something like a PDP-8 or PDP-11 is in many ways ideal because you can see everything that goes on. It is actually possible for one person to understand the hardware, the microcode, and every single bit of the software. For me, that is the great pleasure of small embedded designs. I really think it would be good to have a teaching tool for CS that actually meant that the student could do a project and have a complete overview of the entire thing in this way. I'm far from knocking progress, but there are comments on this thread that are a bit about the kind of alienation we have now between hardware and software - most people have no real idea at all what the hardware does, and use terms like "cache" without even stopping to think about what is going on. So yes, let's have someone build an understandable modern PDP-8. It's less weird than the RCA1802 and easier to get your head around than the 8080.

Egotist: A person of low taste, more interested in himself than in me. -- Ambrose Bierce