back to article IBM PCjr STRIPPED BARE: We tear down the machine Big Blue would rather you forgot

The year 1984 was a watershed for the personal computing market, a year which saw Apple introduce the Macintosh and forever change the way people looked at desktops. On the 30th anniversary of that January release, there was no shortage of coverage looking at the historic launch of the Mac and its impact on the industry and …


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  1. CABVolunteer

    Ah, nostalgia.....

    Are IBM sales folks still a source of self-deprecating jokes? As recounted by our IBM account manager:

    How do you describe Lassie, Rin-Tin-Tin and the IBM PCjr?

    Two movie stars and a dog.

  2. stsr505089

    The original keyboard might have been comparible with that bad joke of the era - the Spectrum keyboard, but its light years ahead of that fitted to the iPad....

    Keys that move ?, what a radical concept....

    1. Fred Flintstone Gold badge

      Maybe it was the abject failure of the PCjr keyboard that inspired IBM to create one of the best keyboards ever later? I know people that have clung on for dear life to their IBM PC clackety-clack keyboard and still seek out its modern equivalent when buying systems because of its tactile feedback (or its weight - these things had serious substance). However, in a modern office, the audible component is somewhat less appreciated, but there are less noisy equivalents now.

      Personally I was more partial to the keys that used a tiny magnet attached to the keys, closing a reed switch. The depth of such keyboards meant they had to be built in, but I rather liked the feel of them.

      1. Vociferous

        The Model M keyboard is wonderful, but also INCREDIBLY LOUD. The other people of your household, office, and possibly surrounding countryside, will not thank you for getting a Model M.

        Someone suggested it was made that loud to simulate the sound of a typewriter, much like how very early cars were made to look like horse-buggies, but it doesn't really sound like a typewriter. On the other hand he sound is, pretty much literally, iconic. Everyone knows exactly how a Model M sounds: it's the sound of all keyboards in all movies ever.

        1. Anonymous Coward
          Anonymous Coward

          "it's the sound of all keyboards in all movies ever."

          Given Hollywood's almost supernatural ability to dry-rape reality whenever computers appear, it's remarkable that they don't foley-in the Model M sound when people type on iPads.

          I can understand juicing up esoteric things, like nuclear control panels or crazy floating holographic user interfaces, that either don't exist or aren't seen too much. But I'm not sure I've ever even seen someone write an email in a movie without - in addition to the gatling-gun typing sounds - showing a user interface with Reader's Digest - Oldster Edition-sized fonts, huge CRT shadow mask pixels (even on laptops), and A SOUND EVERY FUCKING TIME ANYBODY CLICKS ANYTHING!!!

          What the hell?! God DAMNIT, Hollywood; everyone in your audience knows damn well that Outlook Fucking Express does not go BLEEP, BWIP, BWATCH, ZIOPP every time someone sends an email!

          I don't care if you tear up the collective anuses of crap nobody knows about, because it doesn't hurt suspension of disbelief that much, but when it comes to basic computer stuff, FOR THE LOVE OF GOD stop humping and pull your goddamned dick out of the truth! IT HURTS!

          1. Anonymous Coward
            Anonymous Coward

            "Outlook Fucking Express does not go BLEEP, BWIP, BWATCH, ZIOPP"

            Doesn't it? It was watching it do that in the movies caused me never to use it for an email client.

            Ah well, you live and learn. You'll be telling me next that Death Stars don't run DOS, or something.

        2. Wzrd1 Silver badge

          I actually miss the tactile feedback from those monsters.

          I rather miss that other IBM keyboard, the rite of passage model that one had the PFY clean without warning about all of those springs... ;)

          1. Nuke

            @Wzrd1 - Re: Rather you forgot

            Wrote :- "I actually miss the tactile feedback from those monsters .." [IBM Model M keyboards]

            So why did you get rid of it? I'm typing on one now and it will last for ever.

            I read a review of the PCjr back then, and the reviewer said that the keyboard (I suppose the original Chiclet) was so flimsy that he picked it up and gave it a twist. Half the keys popped out onto his desk!

            Reading that destroyed my previous supposition that IBM kit meant quality. I was disgusted. It goes to show that companies with a previous quality reputation should never fritter that reputation away by using their brand name to sell tat.

        3. Alan Brown Silver badge

          You can still buy the Model M. The buckling springs have a unique feel to them.

          You can also buy a nice Cherry G80-3000 (MX 3000) with blue keyswitches which isn't quite as loud and still feels good.

        4. John Tserkezis

          "The Model M keyboard is wonderful, but also INCREDIBLY LOUD. The other people of your household, office, and possibly surrounding countryside, will not thank you for getting a Model M."

          The other people in the houshold and countryside can get stuffed. I have two Model M's, and one new Unicomp.

      2. fruitoftheloon
        Thumb Up

        funny you said that


        I have three Apple ergonomic (adjustable) keyboards and an ADB to USB adaptor, truly the best keyboard design ever. Ebay is your friend...


  3. ThomH

    The 6845 is a zero-colour chip

    All it does is generate sync signals, addresses and indicate where a (text) cursor should go in the signal, and can latch the current logical position if it receives a pulse from a light pen. Actually fetching the video byte and by whatever means turning it into colours is left to other circuitry.

    It is indeed the same chip used by at least the [8-colour] BBC Micro, [27-colour] Amstrad CPC and [16/256-colour] EGA/VGA cards.

    ... and that's the absolute most I can possibly contribute to the conversation. I enjoyed the article but, like most Brits, have no idea how large a baseball is.

    1. Anonymous Coward
      Anonymous Coward

      Re: The 6845 is a zero-colour chip

      It's the size of a rounders ball. Baseball is rounders played by men, with added statistics.

      It occurs to me that the PC Jr. is an object lesson that was completely ignored by Microsoft in bringing out the original Surface tablet; a crippled version of anything is going to be bad publicity, and a good display won't make up for inferior everything else.

      The original 8086 was 4.77MHz; the 8088 was a crippled 8086 with an 8 bit data bus. When, in the early 80s, I designed a low cost industrial CPU for a series of test equipment we were building, I was able to use the NEC V30, a CMOS 8088 running at 8MHz. The entire module (CPU, logic, 64k RAM, firmware in eprom and I/O, plus a 12 bit A/D converter and a 2-line LCD display) used less power than a 4.77MHz 8088 on its own. Intel have got a lot better since, but then they didn't seem to see low power consumption as desirable.

      1. big_D Silver badge

        Re: The 6845 is a zero-colour chip

        The original IBM PC also ran the 8088, that is what made many of the clones, with their 8086, turbo buttons and cheaper prices so much more attractive.

      2. Anonymous Coward
        Anonymous Coward

        Re: The 6845 is a zero-colour chip

        "Baseball is rounders played by men, with added statistics."

        As opposed to American Football, which is rugby for girls.

        1. Anonymous Coward
          Anonymous Coward

          Re: The 6845 is a zero-colour chip

          "As opposed to American Football, which is rugby for girls."

          Sadly untrue. The armour contributes to collisions which are causing an awful lot of brain injuries. Padding is actually more dangerous than its absence.

          Incidentally, re my original comment, it was a joke, even if a very old and overdone one. If you downvoted it for that reason, I tend to agree with you.

        2. Anonymous Coward
          Anonymous Coward

          Re: The 6845 is a zero-colour chip

          Given that American football manages to permanently cripple a rather large percentage of its players by the time they hit 35, I'm not sure I'd so rapidly dismiss the courage / lack-of-foresight necessary to play it, presence of helmets and pads notwithstanding.

        3. Peter Simpson 1

          Re: The 6845 is a zero-colour chip

          American Football, which is rugby for girls

          Very muscular and well-paid girls.

          // actually, it's a two-hour long advertisement for Bud Light

      3. Alan Brown Silver badge


        The V20 was a drop-in replacement for a 8088 - even without tweaking the clock they were 20-30% faster.

    2. Tom 35

      Re: The 6845 is a zero-colour chip

      Not used in the Apple II.

      1. Black Betty

        Re: The 6845 is a zero-colour chip

        IIRC there wasn't a single ASIC chip in the original APPLE ][.

        The CPU had access to memory in the for half of each clock cycle, and the video circuitry access the memory during the other half. This allowed the video circuitry to do double duty, refreshing the DRAM.

        Recall the 8 line video interleave which IIRC saved a whole 2 logic gates.

    3. Vociferous

      Re: The 6845 is a zero-colour chip

      no idea how large a baseball is

      It's one shaftment and 9 barleycorns in diameter, about the same size as a large Pomacea snail. HTH.

  4. Simon Harris

    slow memory?

    The -15 suffix would indicate an access time of 150ns. For a processor with a cycle time of 209ns, that memory's just the most appropriate speed for the CPU.

    1. Anonymous Coward
      Anonymous Coward

      Re: slow memory?

      I may be wrong about this, working from memory, but the cycle time of the 8088 is not one clock but 4. As I recall, the address comes out on clock 1, is latched on clock 2, and the data on the bus is read during clock 4. As a result, 350ns access time allows full speed operation. (In fact I think 450ns is adequate, but building industrial computers with 350ns EPROM added little cost and gave a useful safety margin for when ambient reached 70C.)

      The 8088 in theory overlapped instruction and data, but because it was crippled with an 8 bit bus this never really worked out in practice as it took 8 clocks to read an instruction. R/R instructions might only need 3 clocks, but they still took 8 to read. Not smart.

      Great days, when you could actually put ordinary oscilloscopes on computer circuitry and diagnose what was happening.

      1. Solmyr ibn Wali Barad

        Re: oscilloscope

        Oi, when I were a lad, we used to dream about oscilloscopes. Had to make do with a logic tester, built into the discarded felt pen. Syringe needle, bunch of wires, two crappy LEDs and one 7400.

        Aargh. Shouldn't have mentioned 7400! Those bastards had zillions of 74LS chips to play with, and all they managed to do with them was to turn them into a PCJr!

        /fakes a stroke and slumbers off the soapbox/

        1. Franklin

          Re: oscilloscope

          A logic tester? Luxury! We had an LED with a resistor soldered to one leg. You'd hokd the resistor against the ground pin, touch the other leg to the pin or trace you were interested in, and see if it lit up.

          1. Fred Flintstone Gold badge

            Re: oscilloscope

            A logic tester? Luxury!

            Ah, the delight of the Yorkshire men sketch.. :)

            I switched to using the CMOS 4011 as soon as I could. You could do a lot more with a single battery that way :). Heck, I even used it in SMD form, a good thing I had a Weller soldering iron because they demanded a bit more quality from my then meagre soldering talents :)

            1. fruitoftheloon

              Re: oscilloscope

              I still have my trusty Weller, it is 30 years young now.


        2. Wzrd1 Silver badge

          Re: oscilloscope

          "Had to make do with a logic tester, built into the discarded felt pen."

          It was fun suggesting hooking up a logic analyzer to one of those once.

          The looks I got before they realized I was joking was priceless!

          "Aargh. Shouldn't have mentioned 7400!"

          I think I still have some 74LS series chips in the basement somewhere.

          The last place I saw PCJr units in operation was at Sears, where they were plugged up as kiosk machines to order from the catalog.

      2. Simon Harris

        Re: slow memory?

        You're right - having been used to CPUs that did things in 1 clock cycle, I'd forgotten how slow the 8088 actually was, but it makes sense since it was a multiplexed data/address bus (at least part of it). Just checked the data-sheet and the address looks like it should be latched on the falling edge between T1 and T2, in T2 the data/address bus goes hi-impedance and the read, write and IO/Memory signals are sorted out, and data is transferred on T3 (plus any wait states).

        It looks like memory has from the end of T1 until the end of T3 to sort itself out (about 400ns), so 150ns may well be overkill - mind you, since the design shared the system memory with the video controller, it may depend a bit on how access was interleaved between the two.

  5. Steve Knox

    Ah the 7400 series ICs...

    Time was you could count on 3/4 of any logic board being covered in these beasties. Now consolidation and miniaturization have pushed most of this functionality into the CPU and the south bridge, leaving but a few lone survivors, even these remnants just miniscule surface mount versions of the original, tiny shadows of the vast herds which used to roam motherboards.

    Soon entire generations will grow up having never seen these majestic beasts, except possibly in archives such as this.

    1. Neil Barnes Silver badge

      Re: Ah the 7400 series ICs...

      Some of us are still designing with 74 series ICs - and bemoaning the fact that all the really useful special function ones have gone the way of all flesh. For example, you just can't get an ALU in HC...

      1. Will Godfrey Silver badge

        Re: Ah the 7400 series ICs...

        Very true. Even the 4xxx(x) CMOS series are getting are getting a bit thin on the ground

    2. Tristram Shandy

      Re: Ah the 7400 series ICs...

      You've just brought back an ancient memory. In the early 70s when nobbut a nipper, I used two of this family of chips for a guitar effects unit I'd designed.

      The first chip had some amplifiers on it. I used two of these in series to boost the input signal, so it was heavily clipped and effectively a square wave. This then went to a second chip with a number of divide-by-2 components (flip-flops?), and I used two of these components chained together. I took the input to the chip, the output from the first flip-flop and the output from the second flip-flop, each with its own potentiometer, and mixed them together.

      Result? A big fuzz sound together with the octave below and the octave below that. An awesome sound (well it impressed me).

      1. Simon Harris

        Re: Ah the 7400 series ICs...


        Could the first chip perhaps be a TL074 quad op-amp rather than a 74-series logic chip? Well, they both have a 74 in them!

        1. Vic

          Re: Ah the 7400 series ICs...

          Could the first chip perhaps be a TL074 quad op-amp rather than a 74-series logic chip?

          I suspect he's mis-remembering a little...

          One of the classic guitar distortion designs was to use unbuffered CMOS 4000-series - e.g. the 4009UBE, which gave you 6 stages to play with.

          I can't imagine TTL sounding much cop...


    3. Wzrd1 Silver badge

      Re: Ah the 7400 series ICs...

      "Soon entire generations will grow up having never seen these majestic beasts, except possibly in archives such as this."

      True, most won't believe slamming an original PC HD on the desk to free up a stuck platter.

      Or more commonly, slamming the entire PC for that purpose.

      Hey, it worked and was an excellent stress reliever.

      1. fruitoftheloon

        Re: Ah the 7400 series ICs...

        Me too!

        Then i could mention how i followed up that 'sticky hd' with an intermittent fault on a Mac se keyboard that took 3 months to track down: 'twas the dust particles from the users pipe smoke and high humidity wot done it - shorting the switches of certain keys out every now and then.


  6. MrT

    I'm not surprised the monitor still works...

    ... IBM tended to build good peripherals for their other ranges... the Model M keyboard especially.

    Last IBM CRT monitor I used was an 8514 PS/2 job, back in the era when companies sold a 14" CRT but only 12.9" visible. Not IBM - that thing weighed about twice as much and showed IIRC a touch more than the stated diagonal. 1024x768 goodness until I swapped it for a higher-res 17" Vivitron CRT (with its pixel mask support wires just visible across the screen).

    Nice pictures - it looks like it was cared for through its life, which must mean it's about the best of what's left.

  7. Cyberelic

    Not being a girl, I too have no idea what that ball is like.

    Serious FAIL, go back to square one and rewrite the answer for Engish people...


    1. Anonymous Coward
      Anonymous Coward


      Well, as you can see, the ball diameter is about 2/3 the height of an IBM PCJr. That should be enough for anybody.

    2. Edward Clarke

      75mm in diameter.

    3. DJO Silver badge

      For the fair English rose, the colonial "baseball" has a diameter about a quarter on an inch greater than a decent and proper English cricket ball.

      1. Peter Simpson 1

        inch greater than a decent and proper English cricket ball.

        Well, you see, we use a smaller bat, so the diameter of the ball is increased slightly...

    4. fruitoftheloon

      Engish people, do the speak a different language?

  8. Enrico Vanni

    This might have been a crippled IBM PC, but the engineering stacks up well against the marketplace rivals of the day. IIRC though the PC Junior/Peanut was a good deal more expensive than the BBC (even once you added in the cost of a monitor)/C64/Speccy/Amstrads, and a 16 bit processor (PCJr's USP) pumping through an 8 bit bus didn't impress the lowest common denominator computer buyer of the time.

    The first of the proper 16 bit home computers were already in the pipeline (Amiga and ST) and when they turned up a year or so later the rest as they say is history.

    1. Bakana


      Yep, and stories about the Amiga were already appearing in the literature.

      I read a preliminary report in (I think) Byte Magazine and decided that I knew what my first personal computer purchase was ging to be.

      About a year later, I bought an Amiga 1000 with Half a Meg of RAM, preemptive multitasking, 4 channel stereo sound on the motherboard and amazing color graphics. A machine which I was able to add 8 Megs of additional RAM to a few months later, albeit at a cost equal to the price of the entire rest of the system.

      And the entire OS would fit on a single 3 inch Floppy Disk with room to spare.

      1. Belardi

        Re: Amiga

        I still have my Amiga 1000 and 3000. I think they still work. Back in those days, I paid about $200 for floppy drives. The 2MB memory side-car for my A1000 was originally $1000+ and is heavier than my ThinkPad.

        1. Unicornpiss

          Re: Amiga

          I still maintain that if Jack Tramiel wasn't such a greedy ego and megalomaniac, that we'd be using "Commodore" format instead of IBM format PCs, and possibly even Apple would be a footnote...

      2. Vociferous

        Re: Amiga

        I came to Amiga from a background on C64 (didn't we all?) and low-end PCs, and was blown away by, in order of appearance, the graphics, the sound, and the OS. The OS was the most tinkering-friendly OS I've ever seen, and was of a type we'll never see again: all OS's today are designed ground-up to be defensive, to protect data from outside enemies and from the user. AmigaOS wasn't like that, it was instead designed to be configurable and transparent. (For those who do not know what it was like, imagine a streamlined XFCE linux without any multi-user or security features, where everything is wide-open to tinkering, and you're in the ballpark.)

        1. Wzrd1 Silver badge

          Re: Amiga

          "and was blown away by, in order of appearance, the graphics, the sound, and the OS. "

          I remember three things well from the Amiga. A computer I truly loved.

          The graphics, the graphics and guru meditation error.

          "Right! So, *that* setting is one we'll not play with again!"

      3. 404

        Byte Magazine

        lol! Remember when Computer Shopper was the size and thickness of a medium-sized city's phone book? Roughly 1.5-2 inches? Those were the days... still have some around here...

    2. Simon Harris


      "The first of the proper 16 bit home computers were already in the pipeline (Amiga and ST) and when they turned up a year or so later the rest as they say is history."

      I remember about 30 years ago a Byte article about the IBM System 9000 - designed as a laboratory computer, but with an 8MHz 68000 processor, monochrome 768x480 bit map graphics and built in printer. I wonder if history would have been any different if that had been re-engineered into a mainstream PC.

      1. Alan Brown Silver badge

        Re: 68000

        I used the system 9000. It was awful.

        1. Michael Wojcik Silver badge

          Re: 68000

          I used the system 9000. It was awful.

          I don't know if I'd call it "awful", but I have a weakness for odd and awkward computers. (I still have the empty shell of my first AS/400 down in the basement, just for the sake of nostalgia. If it still had a CPU I'd fire it up occasionally to bask in its dreadfully slow plod through the arcane corridors of OS/400.)

          But I'd agree that the 9000 was less fun than, say, the IBM RT PC. And that was not a well-loved beast itself.

          Certainly around the time the 9000 came along, there were any number of 16-bit machines, mostly using the 68000 or Z8000, and even 32-bitters using the NS32016, on the market. And at various price points and degrees of functionality, from the Amiga and Atari ST to office supermicros like the Fortune 32:16 and Olivetti M20. Not that most of those were necessarily any better than the 9000 (though some probably were), but many of them were either better or much cheaper.

  9. James O'Shea

    Floppy drives

    Ah... as someone who actually used the floppies of the era (on IBM PCs, DEC Rainbows, Apple IIs, and others) I can say that the 360 kB drive was NOT a single-side drive. It was a double-side double density drive. (I have used machines which had single-side drives; Xerox 820s had single-side single-density 8" floppies, 120 glorious kB, for example, and the first Macs had single-side double-density 400 kB 3.5" drives) IIRC the very first IBM PCs had 320 kB DSDD 5.25" drives. Some early Apple IIs had single-side drives; you could use double-side disks in them, you just had to flip 'em over, like a record album...

    The 1.2 MB drives were double-side high density 5.25" drives. Later Macs had double-side double density 800 kB 3.5" drives, and then 1.44 MB double-side high density drives. Some IBM-compatible computers had DSDD 720 kB 3.5" drives, followed by 1.44 MB DSHD and, in some cases, 2.88 MB DSED 3.5" drives.

    1. Steve Knox

      Re: Floppy drives

      A 5 1/4" double-density disk had a 360KB formatted capacity per side. If your drive read only 360KB, then it was a single-sided drive. If it read 720KB, it was a double-sided drive.

      You could, of course, use a 5 1/4" disk as a "flippy" in a single-sided drive, either by using a double-sided disk or by punching one or two (depending on the drive mechanism) additional holes in a single-sided disk. But 360KB is double-density single-sided (not single-density double-sided, because IBM didn't do a single-density 5 1/4" format.)

      1. Charles 9

        Re: Floppy drives

        Other way.

        A 5/14" floppy disk provided up to 180KB of data per side. A double-sided disk had the potential to store up to 360KB per disk. I remember the days when I routinely had to handle them on a 486, and I recalled their formatted capacity to be in the ~350KB range. This is also consistent with other computers of the time like the Commodore. A single-side-formatted Commodore disk reported 664 256-byte blocks free, which equals 169984 bytes.

        If you're thinking a DSDD floppy has 720KB on it, you're thinking of 3 1/2" floppies, which did indeed have that capacity rating in MFM formatting.

      2. Preston Crow

        Re: Floppy drives

        No, 360K was DSDD. I grew up with SSSD (single-sided, single-density) disks on my Atari 800, which were 90K, and you could flip them to use 90K on the other side. (Atari wanted to do double density, but it wasn't reliable enough in 1979.) Double-sided or double density would get you to 180K, and both gave you 360K. Eventually they came out with "high density" 1.2M drives that were also double-sided. I've never seen a PC with 5.25" drives that were anything other than 360K or 1.2M. I think by the time the PC debuted, double density was just as cheap to manufacture, so single density was dead.

        A little research:

        Apparently the PC initially only had single-sided double-density disks that were 160K, though software later updated them to format with extra sectors to 180K. Double-sided drives (initially 320K, later 360K with the same update) came out the next year.

        The 3.5" drives were mostly either 720K or 1.44M. The Mac version used variable-speed rotation to squeeze 800K on an otherwise 720K disk, which made the older disks incompatible with newer drives. We ran into that when we got our first iMac--the 800K floppies for Civilization wouldn't work with any USB drives.

        1. Charles 9

          Re: Floppy drives

          The 3.5" drives were mostly either 720K or 1.44M. The Mac version used variable-speed rotation to squeeze 800K on an otherwise 720K disk, which made the older disks incompatible with newer drives. We ran into that when we got our first iMac--the 800K floppies for Civilization wouldn't work with any USB drives.

          I recall that the floppy drives on Commodore Amiga computers were powered by a programmable controller. In its normal mode an 3.5" Amiga disk could hold some 800KB, but since the controller was programmable, you could do some peculiar formats if you dared. This not only allowed for exotic formats but also for rather unique forms of copy protection.

          1. Bakana

            Re: Floppy drives

            The big advantage to the Amiga Floopy design was that it allowed developers to create Sortware that would allow the drive to read both PC & Mac floppy disks.

            This allowed data sharing across systems that was unprecedented at the time.

            It expanded the "Sneakernet" exponentially.

          2. Alan W. Rateliff, II

            Re: Floppy drives

            Right, the Amiga can handle a lot of formats and there are tons of examples on AmiNet. The DSDD format for Amiga is 880k via MFM with more sectors and no sector gaps as the controller reads a full track at once. DSHD in the Amiga is 1.76MB, but the speed is 1/2 normal as Paula is limited to 250kb/s. This requires a special drive to reduce the rotational speed when an HD disk is inserted, as well as communicate to the OS that the disk is capable of more sectors per track.

            I have copied over plenty of CP/M, MS-DOS, and 1581 disks using my Amigas, including modifying the hell out of the 1020 5-1/4" drive to read 1541 disks and other formats. I have a third-party 5-1/4" drive which is capable of HD floppy reads. Fun stuff.

            Also getting to play with TI-99/4A stuff these days, which are really throw-backs in terms of floppies: original SSSD 90k and what-not on the original WD1770-series controllers. Woohoo!

            The Commodore 64 shares video and system RAM, but things seem to work much better than the PCjr, even at a lowly 1.02MHz. Could be because the VIC-II video processor was designed specifically for this purpose. It also asserts ownership of the RAM buss when needed against the 6510 and the Commodore 64 Programmer's Reference Guide talks about this contention. I think the only time it really becomes a problem is handling tapes as the timing is extremely critical, so the VIC-II display is disabled.

            I had a brief flirtation with the PCjr as my aunt had one. I picked up one up later in life after I had move on to the Commodore 128. A cheap home-made circuit board and I was able to use the PCjr monitor with my 128's RGBI output. The PCjr wound up somewhere else. "Shamus" simply did not hold the same fascination as before. Not to mention the flat double-row of pins disguised as peripheral ports with nothing to differentiate between components other than the number of pins in a block -- made it feel cheap to me, like IBM said "let's put a lot of technology through this beast, but here at the very end we'll just make it seem like poor version of a Heathkit."

        2. Nick Ryan Silver badge

          Re: Floppy drives

          The 3.5" drives were mostly either 720K or 1.44M. The Mac version used variable-speed rotation to squeeze 800K on an otherwise 720K disk, which made the older disks incompatible with newer drives. We ran into that when we got our first iMac--the 800K floppies for Civilization wouldn't work with any USB drives.

          IIRC technically the 3'5" disks were either 1M or 2M, however the necessary formatting and index structures reduced this down somewhat. PCs were the worst for this, getting only 720k from a disk. Macs were a pain with the drives that had variable spin speeds depending on where over the surface the head was - while sounding odd this did make some sense regarding controlling the amount of data in each sector. The Amiga was pioneering in that it could interface with pretty much anything due to a commendable and open DOS (Disk Operating System) that from the start allowed different file systems, or even paramaterised file systems, to be added as long as they complied with the defined API. I vaguely remember hearing about 960K formatted disks however these had to be good quality disks or had even less reliability than normal disks. Atari STs used a largely standard 1M PC disk format.

          For an exercise in enterprising programming though, the floppy drive unit for the Commodore 64 features the same processor as the Commodore 64 itself and it could be programmed to execute remote code.

      3. Richard Plinston

        Re: Floppy drives

        > A 5 1/4" double-density disk had a 360KB formatted capacity per side. If your drive read only 360KB, then it was a single-sided drive. If it read 720KB, it was a double-sided drive.

        No. IBM PC and XT used 5-1/4" 40 track drives. Originally they were full height 40 track single sided 8 sector giving 160Kb. Double sided gave 320Kb. An updated controller could run at 9 sector to give 180Kb or 360Kb.

        Other manufacturers did use the later 5-1/4" DD 80 track drives to give 640Kb, 720Kb or even 800Kb on double sided double density.

        The IBM PC AT had HD 80 track DS to give 1.2Mbyte.

        If it was 5-1/4" and had 720Kb it is likely it wasn't from IBM. (though they did put 3-1/2" 720Kb drives in some models IIRC).

        I had a copy of PCAlien that could read and write dozens of different manufacturer's formats (as long as an appropriate drive was available).

      4. Black Betty

        Re: Floppy drives

        I recall on the Apple ][ (please folk, get it right), the disk drives made no use whatsoever of the index hole for timing or locating the first sector, but instead relied on the motor spinning at exactly 300 RPM and reading and writing to the disk at the bit level. This meant making a flippy was as simple as cutting an extra write enable notch on the other side of the disk. (Or installing a switch which bypassed the write enable sensor entirely.)

        All disk access was done entirely in software. A carefully timed (40 clock cycle loop) chunk of code waited for a specific patten of 10 bit long "bytes" to pass under the read head. Actual data was read and written with a 32 (8 bit) loop.

        To avoid the possibility of a sequence of stored data accidentally mimicking the lead in index "bytes", only 64 of the possible 256 possible 8 bit patterns were originally permitted, and data was written using 5 + 3 bit encoding, meaning it took 3 bytes of space on the disk to store 2 bytes of data.

        As it happens it's possible to store 96 (more?) unique bit patterns without upsetting the index byte apple cart, but the tight timing of the write code made it impossible to take apart three bytes and reassemble them into four (6 + 2 bit encoding) on the fly with code alone.

        As memory got a bit cheaper, buffering and some trickery with lookup tables, solved this problem, and Apple was able to up it's sector count from 13 to 16 per track.

        More exotic coding schemes were introduced by developers to prevent the standard utilities being used to duplicate disks and the copy protection arms race was on.

        And then there was all the fun that could be had with 1/2 and 1/4 tracking, the early read/write heads were too "smeary" to permit adjacent tracks that closely spaced, but because ALL timing was in software, spiral tracking was possible.

        Oh the joys of MUFFIN, FID, Locksmith and boot-tracing self modifying code with custom ROMs. All for legitimate backup purposes only of course.

        1. Kevin McMurtrie Silver badge

          Re: Floppy drives

          Personal computer disk controllers back then did little more than phase lock on the bit stream and convert to bytes. For the Apple ][, each sector was composed of some garbage bits (from write timing errors), FF padding bytes (to recover from write timing errors), a sector header, and a pattern of data bits that wouldn't cause phase lock to drop. There were endless hacks that you could do in code to implement copy protection or boost performance.

        2. Belardi

          Re: Floppy drives

          Floppy drives came in different at different quality levels. So the very dumb Apple ][ drives barely functioned... but for back then, it was a way to make them cheep. Some drives were $200~400, some were $1000. I still have my 1985 C=1571 dual-sided (Whopping 320K of storage) floppy drive that I paid $280 USD. The drive is bigger than my ThinkPad. Half of the space is the PSU.

          It was easily more powerful than any AppleII drive. But by the mid-late 80s, the much better 3.5" disks were becoming common. Because of Amiga, Atari ST and Mac - of course PC won't gain 3.5" as a standard drive until the mid 90s. YEP! In 1993, it was STANDS to get a PC with a 5.25 and 3.5" drives. but they were down to $30 a pop. Win95 made the CD-ROM drive very much a standard.. I've only ONCE installed Windows95 via 14+ floppies for a client who was too cheap to buy a $100 CD-ROM drive... after that, we'd charge extra for the hassle.

          1. Vic

            Re: Floppy drives

            > PC won't gain 3.5" as a standard drive until the mid 90s

            The PS/2 had them in 1987.


      5. David Linsley

        Re: Floppy drives

        360k per side were 80 track drives (double density) with 40 track being 180k per side. Didn't everyone have Cumana drives with a 40/80 switch at school?

    2. Tom 35

      Re: Floppy drives

      I had an Apple II+ and later a //e (still works) with the 5.25 SSSD drive at 147k. I had a purpose made punch that cut a second square write protect hole in a double side disc so you could flip it and use both sides.

      1. Matt Piechota

        Re: Floppy drives

        "I had an Apple II+ and later a //e (still works) with the 5.25 SSSD drive at 147k. I had a purpose made punch that cut a second square write protect hole in a double side disc so you could flip it and use both sides."

        Fancy! We just used a regular round hole punch to make single-sided floppies double-sided. They worked fine for the Atari 1541 (?) floppy drive attached to an Atari 800LE. So much nicer than the cassettes.

      2. Alan Brown Silver badge

        Re: Floppy drives

        The problem with cutting a second notch and flipping the disk was that it mean the floppy rotated "backwards" in its case, which pulled all the grit that had been sequestered into the lining back onto the media - subsequently damaging both it and the heads.

        My high school banned the practice as it noticeably shortened drive cleaning intervals and overall mechanism life.

        Let's not even go into "high quality" floppies which weren't. Price had little relationship to the usability of the disks (Memorex floppies were particular offenders for being "crap" and were the most expensive on the market at the time, about $12 _each_ in 1981)

    3. Anonymous Coward
      Anonymous Coward

      Re: Floppy drives

      "Ah... as someone who actually used the floppies of the era (on IBM PCs, DEC Rainbows, Apple IIs, and others) I can say that the 360 kB drive was NOT a single-side drive."

      As someone who actually owned a PCjr, I can confirm this. Also, there was never a single-sided drive configuration nor was the 1.2MB drive that the reviewer got in his machine ever offered by IBM. This must be a 3rd party product.

      1. DiViDeD

        Re: Floppy drives

        nor was the 1.2MB drive that the reviewer got in his machine ever offered by IBM

        Are you sure about that? I know it was a long time ago, but I remember having an IBM PC-AT back in the day. It had a 5.25 DSDD drive at 360k plus a 5.25 DSHD drive at 1.2 Mb. It also had an EGA monitor offering a staggering 16 colours, a vast improvement on the old CGA XT. Remember how CGA offered any four colourz from a palette of not too many, and every single colourset was shitty?

        Oh dear. I've just remembered the burning babies game. Wonder if it works on W7 64 bit!

        1. Alan Brown Silver badge

          Re: Floppy drives

          The various floppy drives I've had were

          80k ss 5.25" (Commodore external disk drive used for PETs and CBMs)

          180k SS 5.25" FH and HH - IBM

          360k DS 5.25" HH - IBM

          1.2Mb DSQD 5.25" HH - PC

          720k DSDD 3.5" - PC/Atari

          1.44Mb DSQD 3.5" - PC/Atari

          There were rumours of 720kb DSDD 5.25" drives, but I've never ever seen one and the early drives used a drivebelt/capstan setup (with strobe wheel) up until the late 80s when direct drive took over.

          I've never bothered with 2.88Mb drives, but I did use Imation's 100Mb laser-guided floppies for a while. Apart from the nice capacity with special disks, they could read/write a complete 1.44Mb floppy in less than 10 seconds thanks to the ATA interface.

        2. Anonymous Coward
          Anonymous Coward

          Re: Floppy drives

          "nor was the 1.2MB drive that the reviewer got in his machine ever offered by IBM

          Are you sure about that? I know it was a long time ago, but I remember having an IBM PC-AT back in the day."

          I'm referring specifically to the offerings for PCjr.

    4. Colin Bull 1

      Re: Floppy drives

      " Some early Apple IIs had single-side drives; you could use double-side disks in them, you just had to flip 'em over, like a record album..."

      You had to cut the write protect notch first ! We used to do this with single sided disks with very few failures. Whatever happened to Wabash?

  10. adnim

    I am insipred

    to dust off and boot my first PC... An Epson PCe complete with Philips Monitor 80 green screen... Need to find a keyboard with a din plug though.

    1. B-D

      Re: I am insipred

      Please have fun for us both, I long for my old Sanyo MBC-550 and Philips green screen, alas we parted ways many years ago.

      I bought a 4.77Mhz crystal oscillator from my local Tandys store and overclocked my machine, and having read this PCjr teardown I can understand why the Sanyo was clocked at 3.5Mhz now.

      Amazing, and here I am with an Intel Core i7 930 2.4Ghz @ 4Ghz.


      1. Davidoff

        I long for my old Sanyo MBC-550

        Another former Sanyo MBC-550 owner here (mine came with DOS 2.11 and the original cubic Sanyo color CRT), but my main workhose at that time was a Sanyo MBC-1250, a dual Z80 PC with integrated monochrome (green) CRT running CP/M. It was also where I first met WordStar.

        I later upgraded the MBC-550 to a MBC-16 (8088 8MHz XT compatible), and subsequently to the MBC-17 (80286) and MBC-18 (80386DX/16).

        Later when I needed a laptop I got a Sanyo MBC-17LT (80286), and then a MBC-18NB (80386SX notebook).

        Sanyo made really great PCs in those days, and apparently sold a lot of them. It's a bit surprising that they seem to be mostly forgotten.

        1. Alan Brown Silver badge

          Re: I long for my old Sanyo MBC-550

          The MBC550 benchmarked at 0.7 of the original XT's speed. It worked, but it was slow and impossible to upgrade other than some ram + a floppy drive.

          One was my original "PC".

    2. Martin-73 Silver badge

      Re: I am insipred

      You knew this already no doubt, but PS/2 plugs are compatible electrically*, just need an adaptor, or, more in the spirit of the register's readership, a din plug and soldering iron :)

      *This is assuming AT compatible.... if it's XT, all bets are off, I don't think anything emulates them natively but I am sure XT Model M's were available, you might get lucky on ebay

      1. Ole Juul

        Re: I am insipred

        Yes, XT keyboards are not hard to find. the PS/2 to DIN adapters are commercially available.

        For those who are inspired, go have a look at the Vintage Computer Forum where these models are discussed and used by many people. The IBM PCjr is much liked, and one of our members is an expert on these. Check out his web site here. Michael Brutman has also written a very functional and fast TCP/IP suite which runs on DOS 2.0 and up. It includes DHCP, netcat, HTGet, and a very fast FTP. His latest work is a web server which I just experienced showing the above web pages, and running on the the very PCjr we are discussing here. Even with multiple connections, it was fast and responsive. Old timers here will know why.

        1. Unicornpiss

          Re: I am insipred

          I used to have an IBM "clicky" keyboard that had a switch on the bottom so you could choose "PC" or "XT" compatibility.

        2. Simon Westerby 1

          Re: I am insipred

          >> the PS/2 to DIN adapters are commercially available.

          Yes my own "Museum of Computing History"* contains several in the "storage"** department.

          *Collection of computer junk ...


  11. Anonymous Coward
    Anonymous Coward

    It sure is ugly and doesn't really seem to have been engineered with much love or pride? or perhaps they just didn't have access to a good industrial designer?

    1. Franklin

      Ugly, sure, but still more attractive than the PS/2.

      I remember when the first PS/2s came out. A friend and I had been reading about them, so when they showed up at the local computer store, we went 'round to have a look.

      The pictures in the magazines didn't do justice to how ugly they were. Stunningly ugly. So ugly that the first time you laid eyes on one, you were apt to rock back on your heels and wail "what hath God wrought?" in your best William Shatner voice.

      So we went down to check them out. When my friend had recovered the power of speech after being nailed square between the eyes by the ugly, he commented it looked like the business end of a ventilation device for outhouses. "Well, form follows function," I said. The salesperson showing us the wares ducked behind the shelf and broke up laughing.

      To this day, I still can't rightly comprehend the enormity if the fact that someone made them look that way on purpose.

      1. badger31


        I feel the same way whenever I see a Nissan Juke.

  12. Salts

    Bit of a whimp

    "he had the crazy notion that cracking open a three-decade-old CRT display with death-dealing capacitors was somehow unsafe"

    Just use two screw drivers, dig one under the HT lead cap and one on the outside shielding of the CRT and short out, that's the biggest capacitor sorted out :-)

    The harder thing to do, is not to drop it when it bites, if you have forgotten to do this and pick it up to carry across the workshop, you are allowed to swear a lot though :-)

    1. Will Godfrey Silver badge

      Re: Bit of a whimp

      ... and then get wiped out by the far more dangerous 700V DC boost supply which has some real power behind it.

      Bah. Kids today (gerroff my lawn).

      1. Gene Cash Silver badge

        Re: Bit of a whimp

        Aw yeahhhh. I certainly remember *that* popping across two screwdrivers! I couldn't see anything but the afterimage for 10 minutes.

    2. Gazman

      Re: Bit of a whimp

      @Salts, agreed - the kid's chicken, bawk, bawk, bawk, chicken.

      There are ways of discharging these things, you know.

      Now back to repairing with that Mac SE/30...

    3. fruitoftheloon

      Re: Bit of a whimp


      Same trick was needed on the mac plus iirc.


    4. Alan Brown Silver badge

      Re: Bit of a whimp

      Use a 10Mohm resistor on the discharge lead. Saves taking corners out of your screwdrivers.

      There are far more dangerous things inside a CRT case if switched on and some nasty bitey capacitors with nearly a joule of energy behind 'em on the circuit board waiting to pounce if you get careless.

      In the case of a device which has been sitting idle for years the biggest danger is water vapor absorbed into the transformer insulation. It's best to bake the things for 24 hours before powering up. (I had a UPS burn up for this reason after 12 months of being left in a damp storage space - and it took 20 hours to start smoking. Most CRTs go pop within 20 minutes if they're going to blow up out of storage)

    5. Dagg Silver badge

      Re: Bit of a whimp

      It is not only the HT capacitors. the The screen tube is plated inside and out and it is used to smooth the EHT! That can give you one hell of a bite!

  13. Christian Berger

    Refresh on early PCs

    Actually those refreshes used to be done in software. You had 3 timers, one was used for sound, the other one as a "systick" (actually at around 19 Hz for the time) and the third one was set at around 100 Hz and started the refresh routine. So roughly 100 times per second your program would stop for a couple of hundred clock cycles. That's far less than one out of 4 memory cycles. Still there was software which would decrease that frequency to give you more cycles for your software at the risk of memory loss.

    1. diodesign (Written by Reg staff) Silver badge

      Re: Refresh on early PCs

      I understand that's true for various PC things out there. But the docs I'm looking at say the RAM was refreshed by the video electronics in the PCjr: that circuitry governed the first 128KB. From the IBM tech manual:

      "Memory refresh is provided by the 6845 CRT Controller and gate array. The gate array cycles the RAM and resolves contention between the CRT and processor cycles."

      I'm not aware of a DMA controller in the PCjr.


      1. Christian Berger

        Re: Refresh on early PCs

        Ahh, that's actually a side effect then which doesn't cost any additional clock cycles.

        So the CRT controller "steals" memory access cycles from the main CPU. If you swap some address lines around, you can make sure it'll spread all it's data over all pages.

        As far as I know an access to a bit on a page also causes that page to be refreshed.

        Ohh and the missing DMA controller wasn't to much of a problem back then, as MS-Dos didn't support it very well. All system calls were blocking and there was no multitasking. So even when DMA was used, your program still had to wait for it.

        1. Vic

          Re: Refresh on early PCs

          > All system calls were blocking and there was no multitasking

          Actually, there *almost* was.

          Static data in DOS was supposed to live in the Swappable Data Area, which was referenced by reference to the SDA base pointer. In this way, you could hook a TSR to the timer tick, check the InDOS flag to make sure a context switch was safe, then adjust the SDA pointer to effect a context switch.

          It wasn't true multi-tasking, but good enough for rock 'n' roll.

          Sadly, as new DOS versions emerged, more and more static data was put somewhere other than the SDA, so new and interesting bugs suddenly popped into existence on version changes, as context migrated between threads :-(


          1. Christian Berger

            Re: Refresh on early PCs

            Well of course, you could always have an TSR and hook up to interrupts. I've once tried that with a little Pascal program. When I tried it it even seemed to work on Windows. So I loaded it, started a DOS window and there is was. :)

            There are rumors that there were industrial control systems which ran on the PC driven by hardware interrupts, but booted a Windows 3.x as a GUI toolkit.

            1. Vic

              Re: Refresh on early PCs

              There are rumors that there were industrial control systems which ran on the PC driven by hardware interrupts, but booted a Windows 3.x as a GUI toolkit.

              My reason for knowing this isn't all that dissimilar...

              I was building a control/analysis tool with a PC as the user inteface, Due to limitations in the embedded controller hardware, we had to do a data grab in ISR, with a background task to process the raw data and generate trends.

              And then they told me to write the UI in LabWindows. It was horrific. I had to re-write most of the DOS scheduler :-(


              1. Anonymous Coward
                Anonymous Coward

                "I had to re-write most of the DOS scheduler"

                DOS scheduler sounds like something that was in need of being written for the first time, what with DOS being no more than crappy file system and a program loader.

  14. John Gamble

    Redeeming Features

    The keyboard was one of two "redeeming features" of the PCjr -- the other was the (for the time) superior graphics. I had a friend who had a moderately successful game out on the PC, and he loved the PCjr's graphics -- imagine, a full color palette!

    The downside, of course, was that he couldn't actually develop on the machine -- he had to compile the game (using either Lattice or Aztec C) on his PC, then copy it over to the PCjr. An extra nuisance that went for naught when the PCjr was cancelled.

  15. wx666z

    still have one of these

    Last time I tried, it still boots. I did not buy the PCjr, I bought a Tandy 1000SX with 40 meg hard drive for $25 (U.S.), the terms of sale included me hauling off the PCjr, monitor, normal wired keyboard, and a box of books and cartridges. The 1000SX runs rings around the peanut and was cheaper, but still Happy Birthday!

    1. Charles 9

      Re: still have one of these

      That was something I wanted to bring up. IBM may have flopped with the PCjr, yet Tandy was able to get on the map with the 1000, basically a clone of the jr. It gained enough traction that the sound and graphics systems it uses, again the same as the PCjr, tended to be identified as Tandy graphics and sound rather than PCjr graphics and sound.

      1. Epobirs

        Re: still have one of these

        Ah, you beat me to it. Interesting bit of trivia: The Tandy 1000 was originally developed as an Atari system by Tandon, to be marketed as the Atari 1600. It was dropped by Atari not long before Warner Comm. sold it off to the Tramiels.

  16. John Brown (no body) Silver badge

    What they produced, however, was this abomination

    That "abomination" of a keyboard looks remarkably similar to the standard style of keyboard sported by most slimline laptops of today. Then again, my opinion of those laptop keyboards isn't all that different to your opinion of the PCjr keyboard :-)

    I have to agree with what other posters have said about the Tandy 1000 range though. A fairly decent PC clone with the added features of the PCjr compatible sound and extra graphics modes above the then standard of the day, CGA. Some games had setup option to select PCjr/T1000 graphics and sound which really was quite a revelation for a PC of it's day even if still not a patch on Atari, Commodore, BBC and the rest of the home computers.

    IIRC we pulled the 8088 at some stage and replaced it with an NEC V20 which increased the speed by 10-20% (or something like that) and had a side affect of being able to boot CP/M-86 and run older 8-bit CP/M .com as well as newer 16-bit .cmd programmes, which wasn't possible with the stock 8088. That would only run CP/M-86 in full fat 16-bit mode.

  17. B-D

    VGA?, CGA surely

    I note that you refer to a VGA quite often in your write up of the PCjr, surely it used CGA at that time?

    1. Ole Juul

      Re: VGA?, CGA surely

      It had CGA onboard. I'll just quote from Brutman's site:

      The PCjr was built with onboard CGA compatible graphics which was mapped to a range of memory addresses starting at B8000, the same address as the CGA adapter on the PC. The actual memory used was in the first 128KB on the system board - the video circuitry did the address mapping to move memory references from the B8000 address range to the correct place. The PCjr was not designed to use the TTL level monochrome display adapter, which would start at address range B0000.

      BTW, the BIOS provided for 640K memory which some people find useful. It is also possible to actually use up to 736KB on that machine.

  18. Bakana

    Onward to even More Successes...???

    The man in charge of the Peanut disaster didn't quit with that triumph.

    He went on to get himself hired by Commodore which made the mistake of putting him in charge of the Amiga 4000 Development project about a month before they were Supposed to begin ramping up production.

    His first decision was to Halt that production, order the hardware engineers to rip out the SCSSI interface and replace it with the "Industry Standard" IDE drive interface.

    This little "adjustment" only took an extra year, cost Commodore a Years worth of sales and was a major contributor to the company's eventual bankruptcy.

    Needless to say, most of Commodore's Amiga Development team had nothing good to say about the man.

    1. Belardi

      Re: Onward to even More Successes...???

      Really, a year to develop an IDE controller?! The 1200 came out first and had IDE. But I never heard of this being the cause of the demise of the Amiga. C= as whole, killed the Amiga as it was a bit of a sham-tax business. They didn't care too much about being successful.

      Since I was using a VGA monitor on my Amiga 1000 and knew how the A3000 looked, the quality of the de-interlacer in the AGA was horrible. C= should made to many short cuts and the PC Clones were cheaper with better quality output. Unlike the days of the Amiga 1000 or 2000s. hell, the MSRP on my Amiga 3000 was $2500, much cheaper than a $4000 Mac IIx. There was so many problems with C=/Amiga management that I didn't see them lasting long, so I bought a new A3000 for $800(USD) as it was reduced because of the A1200/4000... it would last me a few more years before going to Windows95 *ugh*.

      Sad thing is, it really did take MS 10 years to kind-of equal an Amiga... and longer for Mac.

      1. Bakana

        Re: Onward to even More Successes...???

        There was more than one instance of Amiga fans wondering aloud just how many of Commodore's upper management decision makers were secretly on Microsoft's payroll.

        It would explain a Lot because some of their decisions bordered on Insanity.

  19. MondoMan

    Is monitor really a shadow mask model rather than aperture grille?

    Looking at the photo of the monitor screen, the vertical cutoffs of each stripe segment seem awfully sharp for it to be an aperture grille. I wonder if it's not really a fancy shadow mask, such as the "in-line" shadow mask example (labeled '21" TV CRT Display') shown in the Wiki entry for shadow masks:

  20. heenow

    Had IBM used AMD's Zilog Z80 clone, they would have had a much more capable machine.

    Instead, they helped convince the world that the 8088 was the smart choice.

    The IBM PC is to this day the scab on society it always was, but its progeny is slowly dying off, thank God.

    1. ByeLaw101

      I didn't know AMD did a z80 clone. They did a 8080 clone which was slightly enhanced, but still this would not measure up to a 8088 processor. Z80 was an 8 bit processor with a 64k address space, the 8088 was a 16 bit processor with a segmented 1Mb address space... Apples and Oranges.

    2. Anonymous Coward
      Anonymous Coward


      The Z80 had already run out of places to go, and the Z8000 was a dead end (I remember reviewing it for a possible embedded design and, like the TMS9900, it has some "interesting" design choices.)

      The story I heard was that IBM's minicomputer division really didn't want internal competition, and so the original PC was restricted to an 8 bit bus. Intel designed the 8088 when the 8086 was already in production; it was a Trojan to get the architecture in because once it took off, the 8086 would surely follow.

      The 8086 was far from perfect but it was a good architecture for its time and very easy to use. Unlike the 68000 it fitted in a 40 pin DIL, and board layout was simple.

      In many ways the NSxx032 architecture would have been a lot better for a PC but it just wasn't ready in time. It had a computer scientists's dream of an instruction set and fast integer multiply and divide. But the existence of the 8087 floating point processor really meant that the 8086 could tackle minicomputer applications, and the rest was history.

  21. Joerg

    VGA ? What? VGA was introduced in 1987 with the PS/2 ...

    There was no VGA graphic card in the old PCjr or any other PC at the time.

    PCjr models were using Motorola 6845 graphic chip which was an enhanced CGA.. not even EGA yet.

    1. Tony Sweeney

      Re: VGA ? What? VGA was introduced in 1987 with the PS/2 ...

      The author clearly states "Because the PCjr had no dedicated memory controller, the machine's first 128KB block of RAM was refreshed by the VGA (that's video gate array in this era) graphics chip", i.e. he knows damn fine that while this is the same acronym as The Video Graphics Array standard that we all now know as VGA, the same acronym was used for this logic in the PCjr.

  22. Bela Lubkin

    keyboard hell

    The article fails to mention the single worst feature of the PCjr -- at least the early version which was inflicted upon me.

    Real IBM PCs had 15 characters worth of typeahead: if it was busy while you were typing, what you had typed was stored in a little buffer and played back later, when the next prompt arrived. If you typed too much (the 16th and subsequent chars), it would BEEP! to let you know that the extra chars were being ignored.

    PCjr? Oh my.

    There was still typehead on the PCjr. There was also still a beep. The semantic interaction between these, however, had been diabolically redesigned.

    For some reason, the PCjr wasn't always able to receive a typed character while it was busy. Someone once claimed this was because of its lack of DMA; I never learned why. In any case, it *did* apparently have some inkling that it had lost a character.

    The PCjr's somewhat more modest "bip!" therefore meant "I lost the one character you just typed".

    At least that was the theory. Unfortunately, even the signal telling it that it had lost a character was flaky. What the sound actually meant was "I MIGHT have just lost a character".

    Which meant that as soon as you'd typed 1-2, maybe even 3 chars, you got an audible signal meaning "give up, you have no idea what's in the input buffer now".


    1. DropBear

      Re: keyboard hell

      Oh, this feature seems to have been lovingly preserved to this very day on PCs. Sometimes they just decide that interrupts, DMA, multitasking et al. were all just a bad dream, so diddly squat happens after I type half a sentence into some text box before I realize it and stop. Most of the time, some seconds later, whatever I typed magically pops up all at once - but if the PC is in a nostalgic 80's sci-fi mood, it progressively gets "typed" instead. During such times I really can see how someone might sometimes get the urge to award whoever is responsible for these things a halon treatment free of charge, Simon style...

      1. Terry 6 Silver badge

        Re: keyboard hell

        I've not met this in any of the many PCs I've used. But it's been lovingly recreated ( minus the beep) in Android. Type when the thing is thinking and letters appear briefly on screen, but don't actually go anywhere.

      2. Bakana

        Re: keyboard hell

        It doesn't Have to be that way. I have a friend who types So Fast that standard keyboards Always lose about half of what she types.

        When she complained about this to Dell, they admitted that they HAVE a keyboard theat has no problem keeping up with her typing speed. And, for about twice the Dollars, they will happily sell you one. She's been buying the "high Speed" keyboards for years now because, apparently, none of the manufacturers thinks the average bear deserves the better built keyboard unless they A) complain. B) Cough up a few more bucks.

        1. Anonymous Coward
          Anonymous Coward

          Re: keyboard hell

          Does this problem appear in the form of Randomly capitalized Words, too?

          I'm calling BS on this. My typing averages over 100wpm and I can hit 140+ on a good day; I haven't run into issues on anything from $100 fancy-schmancy gamer things all the way down to $8 Walmart crud.

          Not only is there no mechanism by which I can see what you describe actually happening with a keyboard - and I have personally developed USB HID devices, so I am not completely ignorant of the issues involved - but I find it profoundly difficult to imagine that there is a secret cache of 'high speed keyboards' that I've never heard about, and whose hardware is special enough to make them cost more, but whose presumably extremely low volume doesn't make them prohibitively expensive.

          Further, the amount of data generated even by a supernaturally rapid typist is vanishingly small compared to the bandwidth of pretty much any component made in the last 20 years. You're telling me that modern computers - whose electronics operate so rapidly that the speed of light has to be taken into account when designing their board traces - are incapable of handling the output of your friend's hands?

          I find this somewhat difficult to believe.

          1. Nigel 11

            Re: keyboard hell

            It's believable, but for a different reason.

            The electronics is deliberately slowed down! If it weren't, a short period of intermittent connection between down and up could easily turn A into AAAAA. It's called de-bouncing. Also there's key-rollover logic for when one finger depresses a second key before the first is (fully) released. Sometimes multi-key rollovers.

            I can quite believe that a keyboard that's good for a hunt-and-peck typist would frustrate a fast multifingered touch typist. Also vice versa.

            Personally I get on with even the cheapest Logitech keyboards and can't get on with Microsoft ones, cheap or otherwise. I've never worked out why.

            The fisrst computer I ever used, the keyboard was a teletype at 110 baud.

            1. Bakana

              Re: keyboard hell

              Yep. My friend makes her Living as a Writer.

              Also a trained pianist. Her fingers are just used to going almost as fast as her Mind.

              And, being a New Yorker, she also talks faster than most people sometimes. <G>

              1. Anonymous Coward
                Anonymous Coward

                Re: keyboard hell

                I'm a New Yorker and a trained violinist, so your friend has nothing on me there. :p

                I think I've solved the riddle.

                Someone who was trained on piano prior to typing a lot might well be in the habit of holding keys down for a while - as you do when playing the piano (usually). But keyboards aren't meant for that - they assume tap and release.

                If your friend is playing a computer keyboard like a piano, she's not typing -too fast-, she's overrunning the simultaneous keypress rollover maximum. And that -does- vary between keyboards of varying cost z and keyboards meant for gaming are usually more tolerant for obvious reasons.

                This makes much more sense than the idea that speed is the problem.

                And this is why even the craziest questions are not necessarily crazy when it comes to troubleshooting: "Why doesn't my keyboard work?" ...because you play the piano!

            2. Anonymous Coward
              Anonymous Coward

              Re: keyboard hell

              I am quite aware of debouncing, yes. But

              a) Debouncing only affects the maximum rate of repeated characters, not the delta t between any two keypresses

              b) A keyboard without it would be unusable, and if it wasn't,

              c) It would be cheaper (barely) to make them without it


              d) As I mentioned, I can easily type at 130wpm and almost never have any problems with keyboards ever, while the above poster claims to know someone who constantly loses half the characters typed; given that my typing speed was in the top tenth or hundredth of a percent last I checked, it seems highly unlikely that not only is there some crazy curve-wrecking typist out there, but that Dell secretly makes special impossible keyboards just in case!

    2. Belardi

      Re: keyboard hell

      The PCjr... take a POS computer (the IBM PC), make it a smaller and cheaper POS. DOS systems have always been crap since MS-bought it and licensed it to IBM.

  23. Richard Plinston


    The Fall 1984 issue of byte gives prices:

    64Kb PCJr entry model $599

    128Kb PCJr extended 1 floppy $999

    256Kb PC 1 floppy $1995

    256Kb PC 2 floppy $2420

    256Kb PC XT 1 HD 1 floppy $4395

    In all case the monitor is extra

    Color Monitor $680

    1. Belardi

      Re: Pricing

      It was never a good "home" computer... very expensive and under-powered... My pricing memory starts around 1985.

      Apple IIe = $1000 (without a floppy drive)

      C=64 = $200 (64k / 1mhz)

      C=128 = $400 (128k / 2mhz / 80col display / z80)

      C=128 + 320K floppy drive = $675. (40col color monitor = $200 / 80col monitor = $300)

      Amiga 1000 (256k) = $1200 ($100 for 512k version). included an 880K floppy drive. This computer ran circles around the PC XT and AT computers. It only had a single slot, but it didn't need 6 slots as most functions were built in (graphics / sound / PAR&SEL ports, etc).

      If MS was never allowed to make MS-DOS, just PC-DOS for IBM... there never would have been clones... the IBM PC would have died by 1990 or so. Amigas or Macs would have dominated the desktop computers.. or at least have an more balanced share.

  24. NiD

    An Amstrad 8086 user (ex-user, obviously)

    It's obvious to me that somebody at Oric used that keyboard and really liked it. Somebody else at Oric thought "why not put the whole computer in it".

  25. Valheru

    Software on the PCJr

    My dad bought me one of these when they came out. I was 13.

    He used Lotus 123 on a cartridge and something called PC-Turbo (do not know what it did)

    I played Wizardry, Starflight, and Kings Quest (which had a bug that prevented finishing the game).

    The ROM basic was the only language I programmed on the thing. Funny to think that it was 30 years ago.

  26. mythicalduck

    Chicklet Keys

    So, chicklets where crap back then, why are they forcing them back on us now?! I had to replace my Samsung netbook a few years ago (which had a great, proper keyboard) with an Asus EEEPC 1025 (last of the netbooks I could find), and that has a really atrocious chicklet keyboard.

    If only I could get a nice 10" device with a decent keyboard...

  27. peteola


    I still have my PcJr and it still works. It was a nice little computer in its day with 16 colors and 3 octave sound. No comparison to today's standards. I upgraded mine with a second floppy drive and a parallel port with additional ram. That gave it the only computer with more than 640 K Ram, that gave it 720 k Ram. Fun times in history !

  28. Herik

    Remember programming PC's at this time with Zorland's C manual in one hand and Nortons PC internals in the other. Always wondered what the PCjr was,

    Nortons book always had a star against stuff to indicate that a PCjr did not do things quite like PC, or could not do em at all.

    And 6845 . . . .ohhh I remember that from BBC days.

    Get one of those early IBM lap tops next !.

    1. Neil Barnes Silver badge

      I used that in its Zortech phase

      It was not until I looked it up that I discovered they began life as Zorland. I thought you might have conflated it with Borland, but Wiki tells me they did it on purpose.

  29. Herby


    Just remember, if IBM hadn't used the Intel parts (used a proper chip, like the 68000), Intel might well have been reduced to dust, probably making ram or rom chips.

    Of course for the PC JR they might have used the 68008, which does have an 8 bit buss, but works quite well. As I remember, it could only address 1Mbyte of memory as well. I also note that the 6845 CRT chip is a Motorola chip, as is the CMOS memory chip used in the AT (and all that follows). I suspect that most "bridge" chips have an implementation of the 6818 in them, with the DST transitions that date back that far (and in the USA been changed twice since).

    Life goes on.

    1. Michael Wojcik Silver badge

      Re: Dust??

      Of course for the PC JR they might have used the 68008, which does have an 8 bit buss, but works quite well

      Yes, that would have been a brilliant move: releasing a home version of their office computer, but a completely incompatible one. That would have done well.

    2. Belardi

      Re: Dust??

      The 8bit MC CPU was the 6800 (if I remember right). The 6502 is based off the 6800, eventually made its way to C= CMOS company and ended up being used in AppleII, Atarti and tones of other 8-bit computers.

  30. Nosher

    AMD and Intel

    AMD had been a second-source of Intel chips since their first (reverse-engineered) 9080A - a clone of Intel's 8080 which was released at the end of 1975. By 1976 they had a licence, enabling them to become an official second-source, which they did right up until they were stiffed over the 386 in 1985. See

  31. Stevie


    "an original Mac in mint condition with original packaging and manuals can sell on eBay for thousands of dollars, we found a working PCjr complete with monitor and cables for a much more reasonable price: $250 (£151)."

    Hmm. How much would a mint condition PCjc with original packing material and manuals set you back then, Mr compare Apples to lemons?

  32. Stevie


    "cracking open a three-decade-old CRT display with death-dealing capacitors was somehow unsafe"

    I'm hoping this scaredy-cat "tech" is in actual fact a kno-nuthin intern and *not* a self-described "engineer", otherwise I shall have to ask "Gordon Bennet, don't they teach basic electronics in Physics any more (and thus provide the would-be CRT stripper-downer of the mathematical toolkit needed to calculate safety levels and also provide the methodologies for making power supply capacitors safe)?"

    Besides, even though I've seen a demo of the mighty death-powers of capacitors (as a warning, while qualifying for a shortwave license), they were soup-can sized things from the power supply of a well-obsolete-ten-years-before-the-PCjr-saw-the-light-of-day *mainframe* computer, and they were creatively connected to up the oomph (serving only to fire the desire in everyone present to duplicate the Capacitor Bank of Death and confronting us some days later with the inescapable fact of the impossibility of obtaining the old mainframe-sized electrolytics needed for the task).

    I doubt the actual configuration used in the mainframe would have resulted in more than third degree burns, sundry loss of hair, a refreshing spot of ventricular afib and few fingernails blown off anyway, and if you're not in the market for that sort of action, why are you taking an interest in engineering in the first place?

    "Science is hard, engineering hurts."

    So much for the flat-screen and system-on-a-chip generation. Pfft! 8oP

    1. Bakana

      Re: Bah!

      Funny. When I learned Electronics, they didn't teach us the "Math" of avoiding shocks.

      They demonstrated the unwisdom by shorting out a nice capacitor with an OLD screwdriver and passing it around the room so we could see the melted contact points on the shaft for ourselves.

      Oh, BTW, don't ever bet your life on the "low Voltage, Low Power" source to keep yourself safe. While in the US Navy I got to read the Acident/Safety report for a Sailor who manged to electrocute himself with a flashlight battery. It's not the Voltage, it's how many miiliamps you manage to pass directly through your heart.

      Anything that will "Defibulate" your heart will also Stop it under the right conditions.

    2. Dagg Silver badge

      Re: Bah!

      It has NOTHING to do with the physical size of the capacitor. The mainframe caps you refer to will completely destroy a screw driver, but they are only 5 volts or maybe 12 volts.

      The capacitors inside a monitor / TV or microwave operate at thousands of volts. the EHT section in a TV or monitor is typically 22kv.

      It is extremely unlikely that 5 or 12 volts can give you any sort of shock unless you place the cap on your tongue. 22kv can and will kill you.

      It is the energy in the capacitor that melts the screwdriver and the amount of energy in the EHT section of a monitor is not enough to do any major damage to a screwdriver. But the volotage is enough to punch through the skin and flow through a human body and if it crosses the chest it can stop the heart!

  33. Longrod_von_Hugendong

    Need to send a cricket ball...

    1) then we have something real to gauge size against...


    2) They will know what a real sport it, played by real men. No massive, padded and quilted gloves. Just your hand and the ball. The way it should be.

    In the interest of fairness, I will state I have been to 1 baseball game, it turned out to be rounders.

    1. John 62

      Re: Need to send a cricket ball...

      According to my web researches it was the Gaelic Athletic Association that first codified Rounders. Baseball's US founders modified the GAA's Rounders rules to make Baseball.

      Slightly less well-researched: I also heard on the TV once that a south pacific chief was unimpressed by cricket until he decided both batsmen should play at the same time, and said they should have a bowler coming in from each end.

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