A British Amiga? - didn't quite happen

From May 1986, a trade show report has the Microbox 3 looking like a very handy 68k based board with Motorola’s wonderful new Raster Memory System chipset, headlined as “British rival for Amiga”:

Unfortunately it seems this chipset was never quite released, and Micro Concept’s subsequent adverts paired the 68k with Intel’s 82786 graphics controller (“three 16 bit processors working concurrently”), and sold at £1295, twice the price:

Image-10 includes

  • 68010 cpu
  • 82786 gdc
  • 512k dram
  • 64K sram
  • 256K eprom
  • Floppy disc controller
  • Winchester disc controller
  • Dual RS232
  • Centronics
  • Mouse
  • transputer ports
  • Battery backed clock
  • Stereo sound generator

From this interesting discussion of Moto’s probably unreleased super graphics chipset, the RMS aka 68486:


The announcement of this chipset and Motorola’s statement that it would be available “in September” (they kept saying that for over two years before cancelling it) was the push I needed to switch from the 6809 (Pegasus) to the 68000 (Merlin). Eventually I got tired of waiting and did my own design for video.

A few years later Motorola gave me the datasheets for the chips. I couldn’t believe my eyes: they added 6 wait states to every memory access. That was equivalent of reducing the 68000’s clock from 8MHz to only 3.2MHz, which would make it only about as fast as the old 8 bit micros. Who would want such a machine?

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I think the speed of RAM (of DRAM) was quite a limitation in those days? How did the Merlin’s memory system shape up, and what speed and kind of RAM did you use?

Regarding the RMS, I can totally see the promise – and the eventual disappointment.

I have a table and discussion about DRAM in the text about my modification to make the 512K Macintosh faster. While the focus was on the access time (so much so that normally this was part of the name of the chip) and the range for this got a bit better with each generation (4116, 4164, 41256…), other characteristics got a bit better as well.

Since the RMS chipset insisted on allowing 16KB as an option, it had to be compatible with the timing for 4116 chips. That would have been a good idea in the 1970s but was the wrong decision for the mid 1980s.


Thanks @jecel, that’s an interesting story, and an impressive one.

I was wondering about the use of DRAM’s page mode in computers - I knew Acorn’s Electron used it in a clever cost-optimisation, and I knew the ARM used it as a clever performance enhancement, but I didn’t know about the Mac SE.

More Mac info on this page - it seems an early prototype used an 8 bit bus and page mode, somewhat like the Electron’s use of a nibble wide bus:
Five Different Macintoshes

Hi @jecel I would really love to hear more about your experiences with the RMS chipset by Motorola. To me it seems very strange indeed that such a powerful piece of hardware was marketed for so many years, only to be dropped in the end. If it had ended up in something like a Tandy Color Computer late 1984/early 1985, it would have beaten Amiga to the game!

I will try to send you a mail…

Welcome @Fedor_Steeman! Nice that you found us here. It’s possible @jecel will respond over on this other thread:

(or maybe in a new one!)

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At the pace I am writing that history it will be a while before I get to the RMS part, so I sent Fedor some details via email. But I will also post that there.