Fixing A BASIC Calculator

HPThe early days of modern computing were downright weird, and the HP 9830B is a strange one indeed: it’s a gigantic calculator, running BASIC, on a CPU implemented over a dozen cards using discrete logic. In 2014 dollars, this calculator cost somewhere in the neighborhood of $50,000. [Mattis] runs a retrocomputer museum and recently acquired one of these ancient machines, and the walkthrough of what it took to get this old machine running is a great read.

There were several things wrong with this old computer when it arrived: the keyboard had both missing key caps and broken switches. The switches were made by Cherry, but no one at Cherry – or any of the mechanical keyboard forums around the Internet – have ever seen these switches. Luckily, the key cap connector isn’t that complex, and a little bit of bent wire brings the switches back up to spec. The key caps were replaced from a few collectors around the globe.

Getting as far as booting the machine, [Mattis] found some weirdness when using this old calculator: the result of 2+2 was 8.4444444, and 3+1 was 6.4444444. Simply pressing the number 0 and pressing execute resulted in 2 being displayed. With a little bit of guesswork, [Mattis] figured this was a problem with the ALU, and inspecting the ROM on that board proved to be correct: the first 128 nibbles of the ROM were what they were supposed to be, and the last 128 nibbles were the OR of the last half. A strange error, but something that could be fixed with a new replacement ROM.

After hunting down errors with the printer and the disk drive, [Mattis] eventually got this old calculator working again. For such an astonishingly complex piece of equipment, the errors were relatively easy to hunt down, once [Mattis] had the schematics for everything. You can’t say that about many machines only 10 years younger than this old calculator, but then again, they didn’t cost as much as a house.


  1. garym53 says:

    “The early days of modern computing were downright weird”

    Compared to what??? Fuck me dead – what condescending crap – grow up!

    • John says:

      Agreed. This site has become very far removed from it’s roots.

    • localroger says:

      Well, I’m old enough to remember when these calculators were state of the art (my father’s university had a similar machine made by Olivetti) and even then we thought they were weird. The reason they existed was that, expensive as they seem by today’s standard, a really basic computer like a HP2100 cost five to ten times more than the overgrown calculator did. So they were a niche product for a few years in situations where really slow primitive computing was useful enough to justify them but not the cost of even the most minimal real computer system.

    • DainBramage1991 says:

      I agree with localroger on this. The “computers” in those days were indeed weird. I remember the days when computers came as a kit, and did not include luxuries such as a keyboard or a display (unless you count a row of toggle switches with a corresponding row of LEDs just above it to be an HID). A hard drive was roughly the size of a microwave oven and held a whopping 5K of memory, but we didn’t have to worry about that because at $250,000 we couldn’t afford one. I was thrilled to death when the school computer (we actually had one!) only took 2 and 1/2 days to count to 1,000,000!

      The technology of the 60’s, 70’s, and 80’s was weird because we had yet to come up with any reasonable standard. The Intel Architecture PC (what we knew as IBM compatibles) didn’t become the defacto standard until the early 90’s. Prior to that it was anyone’s game, and there was a huge amount of weird technology around.

  2. Matt says:

    Houses cost $50k? If only they were that cheap here. A house without land is over $200k, then put the land costs on top of that and for a bogan area you are up for no less than $400k, somewhere where you *actually* want to live starts at $600k.

  3. Back in the ’60’s and early ’70’s, HP was doing a lot of work on 16bit mini computers, trying to keep up with folks like DEC, CDC, IBM and the like. Wikipedia has some good information on the predecessor to the 9830, the HP2100 cpu here:

  4. Stephen says:

    With 2+2 = 8.44444 I am reminded of Stanislaw Lem’s satire “Trurl’s Machine” in which the inventor Trurl builds a gigantic calculating machine and asks it what two plus two is. After a long pause a gigantic voice bellows “SEVEN!”

  5. AnubisTTP says:

    The reason this was called a “calculator” instead of a computer by HP was actually a very clever marketing trick. Large companies and military contractors had very complicated rules and approval processes for buying a “Computer” but a calculator was usually treated as a normal piece of office equipment… no harder to get than paper and other standard office supplies. By calling these machines calculators, HP allowed many companies to buy their products that would have otherwise been unable to bypass their internal PHB dysfunction to get a “Computer”.

  6. john says:

    This was my first computer. My dad brought one home from work in 1973, since he worked in the division that made them. They weigh a TON, like the computer’s 15 kilos and the thermal printer on top is close to twenty. They were fast as calculators, not as fast when used for computing, and gaming on that eight dot high, 400 dot wide fiber optic display wasn’t thrilling… but nobody else had computer games at all, so that was something. I still have stacks of audio cassettes full of geneology data for a database my dad wrote, but don’t have a ’30 to extract them. Waves of nostalgia.

    • john says:

      by the way, I’m going with ‘weird’ too. Having spent hundreds of hours playing on one of these, I thought they were odd even at the time. They were calculators: there’s a cursor, and you type in 2+2 and it replies 4, but at the same time it could interpret BASIC commands and could run programs. Rocky Mountain BASIC, the specific dialect these used, was a weird implementation of BASIC. The keys felt weird. When the machine warmed up it smelled like Hewlett Packard plants, a very specific smell that I never ran across anywhere else. They had ROM bays in multiple places, like a door that opened on the side and a bunch more in the back. They would do weird jinky pauses during execution sometimes. And if I remember right, you could type in “4+4, 2+2, 3+3″ and it would reply “8,4,6”. I dunno what that was intended for, but it was interesting. And WEIRD.

  7. SavannahLion says:

    Word of advice.

    Stop using dropbox as an image hosting service.

  8. Space Hobo says:

    Whoa. What horrible future is this, where I need to turn on javascript for an entire mess of google docs sites just to see an image in HTML? Who designed those pages, and how do we enact retribution?

  9. Hirudinea says:

    “2+2 = 8.44444″ What, that’s wrong? But how can it be, the calculator said it!?

  10. nes says:

    Nice writeup. Shame about the images. Please consider switching to a dedicated image host with a nice api such as

    • Mattis Lind says:

      Sorry about the images. I never anticipated this much interest and didn’t know of this article until I got a mail this morning. To solve the problem for the moment I just upgraded to a pro account so it should work now. But I will consider changing to a real image hosting service a soon as possible.

  11. Dave Long says:

    Upon graduating from tech. school in 1972… My first job was as a technician on the production line manufacturing these in Loveland Colorado. They were standard with 2K of memory. We would put every machine in an oven for “burn-in” testing to weed out bad memory IC’s…. which would tend to fail at a crazy rate. I spent most of my first year removing and soldering the memory IC’s and returning the units to the ovens until they would run for something like 72 hours straight without a memory error. I also spent a little time on the 1910A & 1920A production lines. If I recall… the basic 2K machine was $6,000.00 and the printer was about $3,000.00. A few years ago I visited a friend that worked at HP at the same time and he had one of the units. Using a program loop to count from 1 to 100…. it would display the resulting count about once every 3 seconds….. a real speed demon. While working on the hardware I did teach myself to program which led to my later career in programming & I.S. Mgmt.

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