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> In all cases it is possible to add additional memory up to 640k via an ISA card.

Was there any performance difference if you added memory in an ISA card as opposed to directly on the motherboard?

Not on the original PC/XT machines, as the ISA bus was basically the CPU data bus. So regardless of whether you had memory on board or on an ISA card, data transfers were exactly the same speed. On later machines, the CPU would be clocked faster than the ISA bus, so this was no longer true.

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