Back in the early to mid 1980s, I vaguely recall seeing an advert in a (I think) UK based computer periodical monthly (Your Computer, or Computer and Video Games), for a memory peripheral that offered "paging" which would allow the Sinclair ZX81, or the ZX Spectrum (I forget which), to have up to 128 kB (it might have been 256 kB) of memory.

I think that the same company offered a proper keyboard as well, and the company name may have been DK Robotics1 (or something very similar to that). Or, it might have been the same company that offered an alternate [character set?] ROM for the ZX81, whose name I really can't remember2. The links provided by DroidW show that it wasn't dk'tronics after all.

I seem to remember it being a full page advertisement, showing the device, which was a large [vertical?] board full of ICs (behind the ZX81) and explaining how the paging was achieved. There may have been the ability of adding a number of boards into slots, but now my memory is getting a bit unreliable, w.r.t. that part.

I am starting to wonder that, as the board was shown not encased in a plastic shell, maybe it was a prototype. I think that I only saw the ad once. This was not an ubiquitous product, only mail order, not seen in local shops or chains. The ad may also have been in a more "serious", or business type, magazine, like PCW (Personal Computer World), and not in Your Computer or C&VG, as I first thought.

I've looked through my few remaining old magazines and can't find it, unfortunately.

I know that there is a lot of oublié, maybes and mights in this question, but does anyone recall this peripheral, and/or have a photo of the advertisement?

1 dk'tronics seems to be the keyboard producing company, although the Wikipedia page makes no mention of the expanded memory kit.

2 It turns out to be the same company, dk'tronics. Thanks to DroidW, for indirerctly providing the link to the advert for the keyboard and the graphics ROM.

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    FWIW, it was reading this question that jogged my memory, and made me remember the peripheral described above: How can you run a program that is bigger than RAM? May 16, 2019 at 13:37
  • From memory, there were 16kB and 64kB extensions available and, working as programmer, I didn't feel that I could afford even the 16kB version :-) IIRC teh contacts were notoriously flaky and had tendency to lose contact at crucial moments. May 17, 2019 at 6:42
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    @Mawg - Yes, a blob of bluetak was needed between the rear of the ZX81 and the front of the RAM pack IIRC. May 17, 2019 at 6:49
  • You should probably change the title since it's clear from your comments that you're not looking for the largest peripheral - you want someone to find the exact one you remember.
    – pipe
    May 17, 2019 at 13:59
  • @pipe - yes, I can see what you mean, I am probably coming across as being rather picky :-) Although, if someone did manage to find it, then it would be (I assume) the largest commercial memory upgrade that was available. May 17, 2019 at 14:30

4 Answers 4


You might be willing to check this hardware list from World of Spectrum. It contains useful information and magazine advertisements of each hardware piece.

Specifically, DK’Tronics memory expansion kits and DK’Tronics keyboard match you DK’Tronics memories, but the memory expansion kits weren’t as big as indicated in your question: “only” 16 KiB or 64 KiB.

  • Thanks for the link. It was definitely 128k, so it might not have been dk'tronics after all... :-( May 16, 2019 at 13:10
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    I don't recall seeing anything bigger than 16k what would we need 128k for? Also it ran red hot and was prone to wobbling at critical times.
    – Ian Turton
    May 16, 2019 at 17:10

There were various companies producing these of which DK'Tronics was one.

For example Ceedata, Bridge Software, Indescomp and Memotech,

  • Excellent links, thanks. Unfortunately the ads you've highlighted aren't for the product that I have in mind. However, I'll have a peruse of the magazines to try to find it. May 16, 2019 at 13:48

You may be thinking of the BASICare Micro System, an advert for which can be seen here:


In theory, you could use it to expand the RAM of your ZX81 up to a megabyte, although there would be very little use of it past 16K.

  • Yes, I saw this advert, it is similar to the Memotech system, although this one is vertical, whereas Memotech is horizontal. Unfortunately, this is not the one - The one I have in mind was a bareboard, at least the ad showed a bare board, vaguely similar to the AGF joystick interface, except that it was much larger (and possibly had the ability to stack the vertical cards behind each other in banks - although as I mentioned above, I maybe mis-remembering the banks of cards/boards). May 17, 2019 at 5:34
  • Link to Memotech ad. I am starting to wonder that as the board (that I saw in the ad that I'm thinking of) was not cased, that maybe it was a prototype. I think that I only saw the ad once. This was not an ubiquitous product, only mail order, not seen in local shops or chains. The ad may also have been in a more "serious", or business type, magazine, like PCW (Personal Computer World), and not in Your Computer or C&VG, as I first thought. May 17, 2019 at 5:46
  • Another one
    – DroidW
    May 17, 2019 at 8:58

@greenonline, I can't find it but think I recall the advert you are thinking of. Was a set of modules Daisy chained behind a ZX81.. offering number of models including memory and hires graphics etc.

Don't think you have found it yet, but recall it was not often I saw it even though I used to read the same magazines. I remember thinking, why would you spend large sums of money to expand a low cost computer instead of starting with an Apple II?

  • Possibly, but you aren't thinking about the Memotech products are you? I don't immediately remember the high res module, but there may have been, although I'm worried that could be a faux-memory. WRT to expansion, it was easier, in some cases, to spend incrementally, rather than spent a lot all in one go. May 17, 2019 at 9:15
  • There was also the QuickSilva motherboard and hi-res module (and other modules: Character ROM board, Sound board and 3k static RAM board) which plugged into that vertically. May 18, 2019 at 8:11

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