A substantial disadvantage of the design of these machines is that because the refresh cycle is commandeered for other purposes, they're built around an assumption of static RAM. As a result, each shipped with only 1kb at launch and expansions beyond 16kb were rare.
PAL/SECAM compatibility was not an issue on these machines as they could only output black-and-white video signals anyway. Maybe that fouled fooled Lord Sinclair into neglecting SECAM on its following machine, the [[ZX Spectrum]].
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== Clones ==
Timex Sinclair was a joint venture established between the Sinclair Research and Timex Corporation in an effort to gain an entry into the rapidly growing early-1980s home computer market in North America. They produced 2 modified versions of the ZX81:
*TS 1000, introduced in July 1982 and essentially a modified ZX81 with 2 KB RAM.
*TS 1500, introduced in August 1983, it was a TS 1000 with 16 KiB KB RAM and a ZX Spectrum-like case and keyboard.
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