Memory Expansion Modules
1980-81

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Sinclair's memory expansion module, more commonly called a RAM pack, was simply a box with extra memory chips which plugged into the back of a ZX80 or ZX81 to expand the otherwise pitifully small memories of the two computers. A 3K RAM pack (above left) was available for the ZX80, with a 16K model (above right) available for the ZX81. The standard 16K RAM packs were produced by Sinclair, but other manufacturers produced them in larger sizes, up to an improbable 128K. The ZX81's 16K RAM pack was rebadged in the US as the TS 1016, for use with the TS 1000 (which was itself a rebadged ZX81).

Unfortunately, the Sinclair RAM packs suffered from a major design flaw. They plugged into the edge connectors of the first two ZX computers, but were otherwise physically unsupported. This meant that the slightest nudge could incur the dreaded "RAM pack wobble", when the circuit with the computer was briefly interrupted. At best, this meant that any data in memory would be lost. At worst, it could blow the computer's circuit board. Hence many Sinclair users found that a piece of sticky tape or bubble gum was an essential accessory, used to keep the RAM pack in place. Other manufacturers produced more reliable alternatives, designed to rest flush with the table top and the back of the computer (a good example is Memotech's popular offering, right).

The 16K Spectrum could be expanded internally with a kit available from Sinclair Research, so no official RAM pack was produced, although a few third-party manufactures offered external expansion modules.

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© Chris Owen 1994-2003