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Questions tagged [zx81]

For questions about the Sinclair ZX81.

9
votes
3answers
224 views

How can a peripheral work on both the ZX81 and on the ZX Spectrum?

The ZX Printer was made to work with both the ZX81 and the Spectrum (or rather, the Spectrum was made to work with the ZX81's printer!), but these computers have different expansion ports. What I ...
4
votes
2answers
338 views

Why does Sinclair BASIC have two formats for storing numbers in the same structure?

The ZX Spectrum has two formats for storing numbers, both 40 bits, or five bytes. The first is a floating point format, which consists of one exponent byte, and four mantissa bytes. The first bit of ...
5
votes
2answers
402 views

Membrane keyboard robustness

Some early computers used a membrane keyboard (ZX80, ZX81, Atari 400), or semi-membrane with minimal keys (ZX Spectrum). This is because it was cheaper than a mechanical keyboard. Intuitively I would ...
14
votes
1answer
1k views

How do high-resolution graphics work on the ZX81?

The ZX81 has a display file which is treated rather like a serial file. And the CPU generates addresses which the ULA uses to look up the characters' bitmaps from the ROM (Yes, I know the actual ...