Comment by rwmj
12 days ago
The ZX Spectrum had (primitive) video hardware. The GP commenter means the ZX80 and ZX81 which used the Z80 CPU to generate the display and so really were unable to both "think" and generate the display at the same time. On the ZX81 there were two modes, SLOW mode and FAST mode. In FAST mode the Z80 CPU prioritized computations over generating the display, so the display would go fuzzy grey while programs were running, then would reappear when the program ended or it was waiting for keyboard input.
There was an adventure game that showed “The Mists of Time” for 30 seconds during initial map generation - it was a very creative way to describe the analogue tv noise caused by missing video signal.
You're right! I was thinking of the Timex Sinclair 2068. It was preceded by the 1000 and 1500 (ZX80 & ZX81 respectively as you say).