I can usually one-up most anybody when it comes to my first computer (anybody except my mom, that is…more on that later). Around 1981 or 1982, I got a Sinclair ZX81, probably for Christmas or my 11th or 12th birthday. My dad says that ‘we’ assembled it from a kit, which undoubtedly means he assembled it from a kit and I watched as long as my 11-year-old attention span allowed.

The ZX81 rocked a Zilog Z80 8-bit CPU at 3.25 MHz. For those of you who grew up in the 90’s and never saw an ‘M’ in front of the ‘Hz’, that’s three and a quarter megahertz, just about 11000 the speed of today’s PCs (if a cycle got the same amount of work done, which it certainly didn’t). The operating system was BASIC, and programming was accomplished using the pressure-sensitive membrane keyboard (sort of like the pin pad of an ATM or gas pump). The keyboard was only about six inches wide, so typing was strictly a hunt-and-peck affair; even my 11-year-old fingers wouldn’t fit on ASDF JKL;.

Sinclair ZX81 with 16 kb RAM pack and thermal printer. By Carlos Pérez RuizFlickr: ZX81 + rampack + ZX Printer, CC BY-SA 2.0, Link

I remember people not really knowing what to make of it. What is that? A computer. Looks like a calculator. No, just a small computer. So, like a calculator? Nope, it’s a full-blown computer. Looks like a calculator to me; are you sure it’s not a calculator?

I think my interlocutors usually left with the idea that I just didn’t know the difference between a computer and a calculator.

It had one kilobyte of onboard RAM memory. Again for the 90’s kids, that’s about 18,000,000 of what a cheap laptop ships with today (1 kB = 11000 MB = 11,000,000 GB). But not to worry, I had the optional 16 kB RAM pack (that clunky thing stuck to the back in the above picture). The RAM pack immensely increased what you could do with the ZX81, but it was notorious for losing its connection and crashing the computer. From Wikipedia:

The RAM pack was top-heavy and was supported only by the edge connector. It had a habit of falling out of its socket at crucial points and crashing the ZX81, losing anything that the user had typed in. Users turned to using sticky lumps of chewing gum, double-sided tape or Blu-Tack to cure what became known as the “RAM pack wobble” problem.

Much wailing and gnashing of teeth accompanied those crashes, especially when I had painstakingly hunted and pecked in a couple of hundred lines of BASIC code.

What about storage? I had never heard of a hard drive in those days. No, the ZX81 used an off-the-shelf cassette recorder for storage. I believe mine was from Radio Shack, but the one in the picture below is a reasonable facsimile. You could listen to your programs, if you were so inclined, by playing them back on the cassette recorder’s speaker. I recall them sounding a lot like a dial-up modem carrier tone, but it was a long time ago, so I’m not sure.


ZX81 with ‘monitor’ and tape drive. By Mike Cattell, CC BY 2.0, Link

So, yeah, I can (and do) one-up all you fancy folks with your C64’s, your Apple IIe’s, and your TRaSh-80’s (if your first computer had a hard drive, you’re not in the running). Started thinking myself bad, until I tried to pull that shit with my mom. My mom, you see, worked for the Air Force in the mid to late 60’s. That’s her on the right, in the picture below.

Patrick Air Force Base, 1966

Elaine somebody and Theresa Seniuk, Patrick Air Force Base, 1966. Photographer unknown, ditto for Elaine’s last name.

The ZX81 would have seemed like an alien artifact in 1966, and the tape drive I thought was so primitive? My mom used punch cards.

She worked in Procurement, and Procurement at Patrick Air Force Base used the FLAC system:

FLAC’s basic electronic element was the vacuum tube, but it also used crystal diodes for gating. The complete system comprised 1,050 vacuum tubes of 5 different types and 18,000 crystal diodes, but the computer proper used only 420 6AN5 tubes and 15,000 diodes.

The system clock ran at 1 MHz. Addition operations took, on average, 850 microseconds, whereas multiplications and divisions took 3300 microseconds.

3.5 MHz doesn’t seem so bad, now. And I had BASIC:

All programming for FLAC was written in machine language, as the machine lacked any high-level language, assembler or compiler.

Remember me complaining about the keyboard? FLAC used the Friden Flexowriter for input, something like this:


Friden Flexowriter. By ArnoldReinholdOwn work, CC BY-SA 3.0, Link

FLAC also weighed half a ton, took up a medium-sized closet, consumed 7500 Watts, and cost half a million dollars. The ZX81, 15 years later, weighed 12 ounces, was 6.6 inches wide, consumed about 4 Watts, and cost £49.95 for the kit.

For reasons I don’t remember, my ZX81 was replaced in 1983 by a Timex-Sinclair 1000. I know this because my uncle has a VHS video of my 13th birthday (unfortunately never digitized…if you’re reading this, Uncle Ray, I would love to have a copy). I saw the video a few years ago, and I remember my mop-headed, 13-year-old self exclaiming, “Dad, this one’s got 2k of RAM!”


  1. Dunc says

    Yeah, I had a kit-built ZX81 too… My dad was a bit of a hobbyist – by the time he was finished with it, it had a permanent memory expansion (I forget how much), full-size mechanical keyboard, user programmable graphics, three-channel sound, and an interface for a proper dot-matrix printer.

    I seem to recall that the 16kB RAM pack cost about as much as my brother’s first car.

    I still have a ZX81 board in a frame on my wall. I don’t think it’s my original one though.

  2. Some Old Programmer says

    I hazard that I’m older than you (at least for some definition of “my” computer).

    My school in the early-ish 70s had some Olivetti electromechanical calculators (perhaps a Divisumma of some model) and Monroe programmable calculators (my memory says “1265”, but Google image says “1665”). Neither of which were computers, although the Monroes flirted with the line as they had conditional branching and were programmed using octal codes punched into a set of cards. The students would occasionally tell an Olivetti to divide by zero–it would chunk away forever.

    My next school had an full blown computer that I used a fair amount. It was an HP educational basic (likely a 9830A) that had cassette tape storage (we had strict instructions to buy cheap cassettes, as the expensive ones attenuated the signal too much to be reliable), an optical card reader and a plotter.

    In 1978, a classmate’s parents got an Altair 8800–with no offline storage capability at all. We programmed it through the front panel toggle switches and read off any output from the LEDs.

  3. Richard Simons says

    My Dad designed the hoist to lift the door of the Atlas computer in place. It weighed over 100 pounds with all the electronics attached to it and cost several times my Dad’s annual salary. IIRC, it was later matched by the Commodore 64 and, as the world’s most powerful computer, three were considered enough for the whole country (UK). People had no conception of the potential for computers.

    At college, I remember a lecturer bringing in the first electronic calculator. It would add, subtract, multiply and divide, and find square roots.

    I missed out on machine code, but I learned programming with ALGOL and punched cards.

  4. Random Dave says

    In 1976 or so, we had a South West Technical Products 6800 like this: http://www.swtpc.com/mholley/swtpc_6800.htm

    My 11yo self helped solder the many molex pins to the motherboard, and I still have a scar on my cheek to prove it. We later modified a teletype into a keyboard, built a printer, and a cassette interface.

  5. bobmunck says

    First computer: IBM 7070, 1965. (It ran at a blazing 27 KHz.) First computer I owned: Altair 8800, 1975. I was working at DoE in Oakland and going to Homebrew Computer Club meetings at SLAC (Met a lot of interesting people there.)

    My boss at MITRE a few years later was Judy Clapp, one of the first programmers of the Whirlwind I in 1952 and the Air Force SAGE system at MIT and Lincoln Labs.

    Thanks for the memories, Newbie.

  6. Matthew Herron says

    kit-built ZX81

    HP educational basic (likely a 9830A)

    I missed out on machine code, but I learned programming with ALGOL and punched cards.

    South West Technical Products 6800

    IBM 7070…Altair 8800

    TIL some of my readers have serious geek cred.

  7. EigenSprocketUK says

    Clearly I haz zero geek cred in this crowd: my first was an Acorn BBC Model B, which was miles more advanced than a ZX81. I think my parents must have taken a huge breath before splashing out on that: £400 was a hell of a lot of money and junior-me only partly appreciated just how huge a purchase that was for them.
    Years before that, I do remember ogling magazine adverts for ZX81s. And just like the picture in the post above, it was always a close-up camera angle. I remember when my friend’s elder brother got one (a very well-off family) I was quite surprised and a little disappointed that it was nowhere near the size of an electric typewriter, and closer to a paperback novel. Didn’t stop me being extremely jealous….

    • Matthew Herron says

      Henceforth and forevermore, let it be known throughout the land that if your first computer used an 8-bit data bus, your geek cred shall in no wise be impugned.

  8. Curt Sampson says

    Even if you ignore that it ran at over three times the clock rate (though admittedly you needed to put up with a flickering screen to compute at full rate on the ZX81), the Z-80 CPU was a considerably more powerful beast than the 6502 used in the Apple, Commodore and Atari machines.

    As an example, consider the registers. The 6502 had an 8-bit accumulator, which was the only place you could do most numeric operations, and a pair of 8-bit index registers, useful for not much beyond holding counters for offsets into memory.

    The Z-80 had seven eight-bit accumulators, six of which could be used in pairs to manipulate 16-bit values, and beyond that another pair of 16-bit “index” registers which, as well as being usable for indexing, were pretty much as flexible as the other accumulators. (They could even be used as pairs of 8-bit registers if you were willing to use undocumented opcodes.)

    The Z-80 also had a larger, more powerful instruction set and more addressing modes, which I won’t go into here to avoid tedium.

    These days I joke about the 6502 as being an early RISC machine with just one register.

    (All that said, I used both the Apple II and the Timex Sinclair and far preferred the former, and still would have even if the Sinclar had had a disk drive.)


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