The Sinclair ZX81: Small Review of a Small Computer

The ZX81 is the recent entry from Sinclair for lowest cost computers, and a very delightful entry it is. It retains the innovative features of the older ZX80 such as single-keystroke keyword entry and a very compact case. The new machine has an 8K ROM that contains the BASIC interpreter, the video display firmware, and a floating-point calculator that offers about the same amount of power as an Apple but at about double the speed. The BASIC interpreter allows variable names of arbitrary length, so you can write programs that are very nearly self-documenting.

The basic system also includes PEEK, POKE, and USER functions to facilitate machine language programming for the Z-80A processor. There is no doubt that the software resident in the system comes from a very smart group . . . they describe themselves in the excellent BASIC programming manual as “a small firm of Cambridge mathematicians.”

Sinclair is an English company and there is one English chip in the machine – a large universal logic array which executes the video, cassette tape and address decoder functions. The remaining four of the IC’s in my kit are of Japanese manufacture.

The small keyboard is not as hard to use as it might seem and is, in fact, just right for young fingers to practice the marvels of computing. If you should wish to add a larger keyboard, nothing more is required than a naked keyboard wired into the ZX81. About $1 in parts will add a direct video output, so you can use a composite monitor instead of a television set as your display device; another 50 cents worth of parts will fully decode the ROM address space to allow for easy expansion of the control program.

Sinclair and others offer RAM extension boards that start at 16K bytes and $100. Don’t take seriously the rather disappointing article in the January issue of BYTE. . . it is neither impossible nor undesirable to add more than 16K of RAM to this machine. I am equally pleased with its performance as a BASIC learning machine as a smart process con¬ troller, for which I predict it has a glorious future. It costs $150 assembled or $100 in kit form, which includes a UHF TV modulator and a calculator-charger type power converter. All in all, a rare, excellent bargain!