Retrotechtacular: The $5,000 40 Pound HP Classroom Computer

See if you can talk your local school district into buying a computer that costs about $5,000 and weighs 40 pounds. That was HP’s proposition to schools back in 1968 so really it is more like $35,000 today. The calculator had a CRT display for the RPN stack that you could mirror on a big screen. You could also get a printer or plotter add-on. Pretty hot stuff for the ’60s.

The 1970 videos promoting the HP 9100, posted by the [Computer History Archive Project], shows something we’d think of as a clunky calculator, although by the standards of the day it was a pretty good one with trig functions and a crude programming capability.

You could save your program on a magnetic card that looked more like a credit card than HP’s later magnetic cards for calculators. It also had an optical mark sense reader so students could program cards at home using a pencil, presumably running test programs or submitting homework answers.

Honestly, this seems hokey today, but back then this was pretty amazing stuff. Graphing calculators did take over the classroom, but not until the students could have their own for a bit more reasonable price.

Apparently, Bill Hewlett said that they would have called the 9100 a computer, but it would have confused their customers because it didn’t look like an IBM computer. Naming it a calculator cued customers that it was something different. The device had no integrated circuits and was similar enough architecturally to an Olivetti Programma 101, that HP was forced to pay about $900,000 in royalties to Olivetti.

If you watch the video to the end, you’ll see a 1970s-era physics instructor show how to use the 9100 to explain a body in motion. Not exactly a Zoom class, but pretty close for five decades ago. If you want to check out the slick marketing brochure for the machine, it lives as a PDF file. There’s even an example of plotting the frequency response of an LC network. You can even read some electronics and other types of programs for the beast in the HP Computer Museum.

It is a long way from an HP 9100 to the HP Prime. But probably no further than the 9100 was from a CURTA.

21 thoughts on “Retrotechtacular: The $5,000 40 Pound HP Classroom Computer

  1. We had one at our school. RPN was really mindbending when you already made your first steps in BASIC on a Commodore PET. And the printer was using a metal-coated paper where the characters were actually burned into the paper. All in all it was already outdated when I first got hold of it, but the teacher always made a big show of it when he opened the locked wood case where the calculator resided. Definitely a part of computing history. Happy that RPN did not really catch on except for some HP programmable calculators.

  2. I loved that early hardware. My first paid programming gig was on an 9810 in the early 1970s. I was never lucky enough to play with a 9100. On the 9810, the normal mag cards held short programs, but if you had the 10 or 11″ cards you could holder longer ones (useful if you had the memory expansion). The lab I worked for used them to control all sorts of automated test hardware using the digital control cards. Very cool tech for the day!

    1. My first assignment at my first (paying) programming job was to write a program for the HP 9820. It had an HPIB interface card and talked to nuclear instrumentation in a CAMAC crate. (This was in the Quality Control lab of a nuclear fuel manufacturer. Yes, be very afraid. :-)

      I wrote a beautiful program, given the limitations of the language. Meaningful labels, structured code, etc. I got it working and *then* they told me the development machine I was using had twice as much memory as the production machine. I started cutting and optimizing (for space) and sweating pretty hard. I got it to fit, but it was a *very* close thing. Taught me a valuable lesson, though.

      Aside from that, it was fun. HP made great stuff back then.

  3. One of my first employers had one of those. Even though I did not work in the office, I wrote a little payroll program for them. Each employee had a separate mag card. Fun little machine.

  4. Neat machine. Sure don’t need ‘fancy’ machines to get basic concepts across!

    Still use my HP-15C and HP-16C. Had an 11C, but my sister got that when I went to the 15C for collage. RPN just makes sense and most of us at school preferred it…. whether it was then engineers or the the computer science people. Still do.

  5. Cathode Ray tube as a display, RPN with a three element stack only (compared to the four later on with HP calculators), we had a plotter connected having a lot of fun plotting electric fields as well as birthday cards

  6. Thanks for mentioning the MoHPC!
    (Museum of HP Calculators.

    I find it a bit bittersweet,
    the more people learn about the old HPs, the less likely they’ll be tossed in the trash.
    But, then, more people will become collectors, driving the prices up!
    B^)

  7. It is rather odd how strong the connection is between computers and education. Even before they were actually all that useful, people thought everyone needed to learn about them, and that they could be used to help people learn other things.

    Even today, a quick glance at Reddit reveals that most code written outside working hours is actually meant to learn something and explore a concept, most discussions on languages have a few “C is a great language because of how much you learn” comments, etc.

    It’s created some amazing progress, but I wonder if some areas computer tech wouldn’t be better without such a strong academic connection, and if there’s really all that much evidence for all the bizzare ways they’ve tried to use computers for education.

    Obviously computers are now helpful just about anywhere, simulator training is great where applicable, and 1-1 digital replacements for physical textbooks and video taped are convenient.

    But it still seems like all the “Everyone should learn to program” and “Math an essential life skill” are stil promoting it is fairly pure academic excercise.

  8. The MIT engineering library had one in the main reading room for student use. Didn’t have the printer option. I used it to calculate coil values for resonant circuits. Before that I was using a mechanical (Freiden) calculator, that could actually do multiplication and division.. (Supposedly they even had a model that did square roots) Until I stumbled onto it, (I was in high school) I was doing things mostly by hand, with heavy reliance on a table of logarithms.

  9. I remember the company I worked for in the early ’70s had one. Only one person was trained/allowed to use it. We all used HP-35s in the field and there was always a log book and slide rule in the glove box! Still have a 12-C and a 48-GX and use them regularly.

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