This is designed to be a simple set of questions and answers - please no general chit chat in here - keep it focused to help new users!
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
Iss 3 ZXVid
TS 1000 iss 3, ZXPand AY, ZX8-CCB, ZX-KDLX & ChromaSCART
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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Apart from the Z80, the ROM chip and the RAM chips, all the remaining chips were inexpensive standard 74LSxxx series parts.
The ZX81 was designed to lower the cost further. Hence the ULA replaced ALL the standard 74LSxxx series parts. A keyboard made of a plastic membrane also lowered the cost.
This left the ZX81 with a smaller (and cheaper) PCB, with only four chips or only five chips. The chips are:
- Z80A or more likely a NEC unlicensed clone (NEC D780C-1) CPU
- Mask ROM
- 1K byte SRAM chip
- Two 1K by 4 bit SRAM chips (combined giving 1K byte)
At that time, all RAM was very expensive. SRAM was very simple to use, and did not need any support chips. Whereas DRAM chips for larger amounts of RAM were cheaper per byte, but needed support chips. Complexity that Sinclair did not want.
To see an indication of how much DRAM cost, look through adverts in the magazines of the time and compare the cost of a ZX81 and that of a 16K RAM pack for it.