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The ZX80 only came with 1K of RAM, which had to be shared between program and screen memory, so many customers bought the Sinclair 16K RAM pack, which plugged into the expansion bus (the edge connector at the back, that basically allowed access to the system address and data lines).

The expansion bus was also used for connecting peripherals such as the Sinclair spark printer, and third-party disk drives and joysticks.

How was it possible to use peripherals and the RAM pack at the same time? Did one or the other have a pass-through for the expansion bus?

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Did one or the other have a pass-through for the expansion bus?

There was no other peripheral (by Sinclair) for the ZX80 than the 1..3 KiB static RAM or the later 16 KiB DRAM version (*1).

Most (*2) third party vendors made theirs offering a pass-through.

Did one or the other have a pass-through for the expansion bus?

When the ZX-Printer came for the ZX81 (*3), it had a pass-through and was meant to be plugged before the RAM-Pack.


*1 - The only other "expansion" Sinclair ever offered for the ZX80 was the ROM Update to turn it into a (FAST only) ZX81.

*2 - I own at least two different I/O expansions without. I'm still puzzled what they expected users to do with an I/O port and not enough RAM for even the most simple program using it.

*3 - Usable with the ZX80 with ROM-update installed.

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