THE COLLECTORS GUIDE TO THE:
SINCLAIR ZX81 by using the FAST command. On powering up the computer it is set to what is known as a “compute and display” mode. This means that the computer refreshes the information on screen while it processes data. The computer struggles with updating the screen and processing data at the same time. The following short program demonstrates this: 10 FOR A=1 TO 100 20 PRINT A; 30 NEXT A
seconds. It’s still not as fast as a ZX Spectrum but it is a much needed boost when processing data. Officially the computer displays a graphic resolution of 64 x 48 using graphical symbols. However, a resolution of 256 x 192 is possible using a 16K RAM pack and some clever programming. While there’s no audio hardware, people have produced sound out of the computer by two methods. By rapidly cycling between the FAST
The above took 36.7 seconds to reach the end of the program, where as a Sinclair ZX Spectrum running at 3.5 MHz would complete it in under 2 seconds. Using the US version only makes the situation worse, as NTSC requires the screen to be updated 60 times a second instead of 50. It would takes a whole minute on a NTSC system. The “FAST” command fixes this, it forces the computer to only update the screen when it isn’t processing data. Typing the FAST command causes a irritating flash on screen each time a key is pressed and when a program is running only displays a blank screen. It will however display the screen for INPUT statements and the PAUSE command. Using FAST mode the above program will count out 1 to a 100 in a little over 10 CLIVE SINCLAIR INTRODUCING THE ZX81
THE MEMBRANE KEYBOARD OF THE SINCLAIR ZX81
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