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What was the largest cartridge produced, or possible, for any 8-bit home computer?

That is, the later 8 or 16-bit console cartridges could be surprisingly large, up to several megabytes in some cases, but as I understand it, the Commodore 64 cartridges were limited to 16K of ROM, and I don't remember other home computers going much beyond that. Were there any that did?

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    The Acorn BBC Master used sideways ROM techniques in its cartridges. – Chenmunka Nov 14 '17 at 11:35
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    This has been flagged as "too broad". I don't see how it's any broader than Largest ratio between base and maximum RAM though. – wizzwizz4 Nov 14 '17 at 19:04
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    @wizzwizz4 I agree, the applicaiton of rules for 'on topic' is still rather random, isn't it? – Raffzahn Nov 14 '17 at 19:18
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    @Raffzahn (This is why we're still in beta.) We need a meta consensus. – wizzwizz4 Nov 14 '17 at 19:53
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    Meta question about this question here. – wizzwizz4 Nov 18 '17 at 11:25
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Simple Answer: Unlimited and Many

Ofc, every system can only reserve a certain amount of real address space for cartridges, but then there is Bank Switching. Just take the original Atari 2600. Address space for ROM was 4 KiB, and many early games only used 2 KiB ROMs. But already in 1982 Burger Time came in a cartridge with 16 KiB ROM and some sort of bank switching. That's already more than the whole address space of the 6507 (8 KiB). Later even 32 and 64 KiB cartridges have been made.

After all it's the same as with every memory expansion. The Apple II only offered 12 KiB of deselectable ROM address space for expansion, but already Woz' language card filled these 12 KiB address range with 16 KiB of RAM. Saturn & Co later on squeezed several Megabytes in.

These are the same techniques used in later games to get squeeze large amounts of game data into a linited address space. Usually the logic to enable the switching was part of the cartridge. As Chenmunka already mentioned, some systems, like the BBC, Memotech MTX, Exidy Sorcerer and other 8 bit machines already included mechanics, or at least protocols to handle expansions larger than the provided address space (window) in their basic design. Many of them enabeling RAM or ROM in the megabyte range.

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    Further to this, I'll wager that, practically, the largest commercial 8-bit home computer cartridge will have been a release for either the CPC+ or the 64GS as both were last-gasp efforts at extending the lifetime of 8-bit computers, appearing in the early-'90s, by which time ROM was a lot cheaper. That's where I'd look first if the author wants an actual numerical answer. (Much easier to find: the largest Master System game was 512kb; the largest NES game was 768kb. Neither is a computer, but that partly speaks as to contemporaneous economics) – Tommy Nov 14 '17 at 16:43
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    @Tommy Some of the late European cartridge releases for the C64 from the GS era were up to 8 mega-bit (1024KB) in size, yes. The Shadow of the Beast for C64 on cartridge is one example that springs to mind. Even the pack-in cartridge with multiple older games on it was a 512KB cartridge. – mnem Nov 14 '17 at 18:56
  • I didn't see the 1MiB expansion for the C64, but I can confirm there was one for 512KiB. – Ed Grimm Jan 24 at 4:06
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This isn't an answer to the question, but an interesting tangent. I thought it was worth mentioning on while discussing the topic, though.

As Raffzahn points out, cartridges didn't have to just be static ROMs (or EPROMs as many of them actually contained), but could also have active circuitry that enabled bank switching or other features. In many home computers, the cartridge interface was just an extension of the system bus, so the cartridges could actual add any additional hardware to the system that would sit inside the required form factor.

An interesting example of this was the Video Chess cartridge for the TI-99/4 and /4A computers. These computers by default had 16.25KB of RAM (16K of slow DRAM and 256 bytes of faster SRAM used by the processor as a scratchpad due to its lack of useful registers). The developer of Video Chess decided that this wasn't enough to get the computer to play a good game of chess, and therefore used the cartridge to fill the entire memory space of the processor (other than the parts that were needed for ROMs) with additional RAM, leaving the system with 42KB of RAM, according to the specs here (although I'm a little dubious, because those specs suggest the total address space used exceeds the processor's address space, but only by a couple of KB... I have a suspicion that something has been reported incorrectly, somewhere), which was basically an enormous amount of memory for a home computer in 1979.

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    That is an interesting find. I find a few things confusing: a) it says 42 KiB RAM in the table, but 28KiB of 'active memory' below b) The TI99/4 offers only 40 KiB of extension space: 8 KiB at >2000 and 24 KiB at >A000 for RAM and 8 KiB at >4000 for ROM. c) Puting 26 KiB of ROM and 42 KiB of (static) RAM in a TI cardridge seams almost impossible for 1979. Even more with a 70 USD price tag. --- Now, if we assume a typo and go for 2 KiB RAM (the precedign 4 being an artifact, this would with 26 KiB of ROM add up nicely to 28 KiB 'active memory'. Just a quick guess. – Raffzahn Nov 28 '17 at 0:31
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    Ok, got it - and that page got it wrong. There is NO RAM I just opened one (Video Chess is one of the most common TI cartridges). The board is a standard TI cartridge board for up to 1 ROM and 4 GROM. All 5 places are in use. 4 GROMs (CD2020ANL..CD2023ANL), so these are 24 KiB of GROM, as described on that page. The 5th is clearly an 8 bit wide ROM labeled CN19310N. TI had 2 KIB and 4 KiB ROMS fiting that socket. So my final verdict is that this cardridge holds 24 KiB GROM with interpreted (GPL) code and 2 (or 4) KiB bytewide ROM holding interpreter extensions specially made Video Chess. – Raffzahn Nov 28 '17 at 1:03
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    Addendum, Here's a nice (italian) site showing several pictures of TI cartridges, including Video Chess. webalice.it/facele/ti99.htm The TI 99/4 is an awesome machine. The only reason why it didn't push every other home computer out is a classic example how management shoots itself in the foot. – Raffzahn Nov 28 '17 at 1:11
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    Interesting. Particularly interesting because this site wasn't where I found the original information that the cartridge contained a RAM expansion (which I've believed since the time I owned it in the mid 80s), so it must be a myth that has been circulated somewhere and copied onto that site from some source or other, but unfortunately I have no memory of where I got it from. – Jules Nov 28 '17 at 14:00

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