One of the things that distinguished the ZX81 from its predecessor the ZX80 was the fact that the screen didn't go off when your program was running, which made it much more useful. The CPU was still driving the screen but interrupts ensured that it was doing so when needed so actual code execution was limited to times when it wasn't needed for the screen.
This of course made it exceedingly slow. Not helped by the fact that the BASIC - squeezed into 8k - was also very slow.
You could write a surprisingly big program in the 1k RAM though due to the fact that all the BASIC keywords were stored as one byte - and had to be entered using one keypress. Which given the quality of the key (not actually keys) board was a relief.
Truly a machine built down to a price, but with considerable ingenuity!
This of course made it exceedingly slow. Not helped by the fact that the BASIC - squeezed into 8k - was also very slow.
You could write a surprisingly big program in the 1k RAM though due to the fact that all the BASIC keywords were stored as one byte - and had to be entered using one keypress. Which given the quality of the key (not actually keys) board was a relief.
Truly a machine built down to a price, but with considerable ingenuity!