The BBC Master 128 has 3 empty expansion ROM sockets and 2 cartridge slots, which seems like a lot of potential. I have already discovered that it is common to add an expansion ROM to support a filing system, but that still leaves 4 ROM+Cart sockets.

I understand that "Sideways ROMs" added via these sockets provides bank-switchable 16KB space that could be used for any sort of ROM software. What actual software was made, besides filing systems? What other expansions/peripherals, besides just "Sideways ROM", has been added to the BBC using the cartridge slots?

NOTE: I'm not looking for an exhaustive list of products. If there are a lot of uses, then just a sampling of the variety available would be great.


3 Answers 3


The cartridge port first appeared on the Electron's Plus One expansion; those on the Master vary the meaning of a few pins but are mostly compatible — ROMs should work without modification (subject to the software, of course), but hardware is likely to be machine specific. The full pinout, including documentation of the machine differences, is contained in this Acorn application note.

A hypothetical Master cartridge gets enough information to expose registers, receive and provide audio, track composite sync and provide input to the CRTC's light-pen pin (which causes current output position to be latched).

That being said, there wasn't anywhere near as much hardware available as for the Electron as I recall. So, mostly it was the defined software ROM types (as per Chapter 17 of the New Advanced User Guide, but possibly more easily digested from the Electron Advanced User Guide because the same topic is stretched to four chapters, 8–11, and that PDF has been OCRd):

  • language ROMs — anything that provides an environment: Forth, Logo, BCPL and Lisp being popular options that were actual languages but also View (the word processor), ViewSheet (the spreadsheet), and other traditional applications;
  • services ROMs — anything that provides transient functionality: filling systems mainly; and
  • serially accessed ROMs — these approximately contain the byte image of a tape, which the OS then loads just as if it were a [fast] tape. Not that useful on a Master where the usual storage is fast anyway but you could use the Electron cartridges, which generally are the early Acornsoft games: Hopper, Starship Command, etc. Likely Master compatible, as they just select a mode and then go.
  • Great answer. I was wondering if you know of any more details about a Forth language ROM?
    – Brian H
    Jun 13, 2017 at 11:16
  • 1
    I was thinking of the Acornsoft Forth; you can download the manual from 8bs.com/othrdnld/manuals/applications.shtml and there are also 'fitting instructions' there for the original release, which was a single ROM chip that you fitted to your BBC. The cartridges were a way better to package the loose chips and as per TonyM's comment above cartridges were available into which such loose chips could be installed; chrisacorns.computinghistory.org.uk/Computers/… confirms that it was also available directly as a cartridge.
    – Tommy
    Jun 13, 2017 at 11:24

Some popular expansion pack features:

  • Programming languages (e.g. BASIC, D-DOS)
  • File managers
  • Office suites (e.g. View, Inter-Chart, Wordwise Plus)
  • Hardware drivers (e.g. Epson Printmaster)
  • Development Utilities
  • Emulators
  • Modems (e.g. Master Modem)

Further reading:

  • 1
    There was also RAM that allowed you to load the code of a normal ROM from disc/tape and then use that as a normal Sideways ROM. Thus if you acquired the ROMS you could have the choice of more than 4 different languages.
    – mmmmmm
    Oct 1, 2018 at 21:30

I used to keep my own cartridge to use on the 10-or-so BBC Masters we had at work. I'd plug it in when I started work on one.

It was just my favourites...Wordwise (WP) and Exmon (debugger/disassembler), I seem to remember.

  • 1
    Welcome to Retrocomputing. Remember that you can get a badge for re-reading the tour.
    – wizzwizz4
    Jun 10, 2017 at 17:29
  • @TonyM did you make that cartridge yourself? Jun 10, 2017 at 21:02
  • @Wilson, I wish I was so grand and adventurous :-) Acorn made a ROM carrier cartridge, you could buy them and we had a few. I just copied the two ROMs and pushed them into the carrier's sockets. Have a look at www.computinghistory.org.uk/det/33659/BBC-Master-ROM-Cartridge-(x2)/
    – TonyM
    Jun 10, 2017 at 21:11

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