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There were also 8-bit home computers (like the Amstrad CPC and C64) where a different memory bank would be accessed depending on whether the CPU would do a read or write access, e.g. a read would access a ROM bank, but a write would access a RAM bank at the same address (usually called 'shadow ROM').

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Huh? How do you read from the ram after you write to it?

You bank switch then. A common use would be to e.g. be able to use the ROM to load code into the RAM under the ROM and then bank switch, but also e.g. for extensions where you might want to first copy the ROM into the underlying ROM, and then patch whatever changes you wanted into before bank switching.

And sometimes you also don't need to read the written data back (for instance when writing to video memory).

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