The ZX-81 was introduced in March of 1981. It has a membrane type keyboard which doesn't allow you to type in BASIC keywords, instead you have to push and hold a function key while hitting a specific letter key and the BASIC keyword is printed on the screen. The computer has no color or sound and comes with only 1k of user RAM in the basic unit. Despite these shortcomings the ZX-81 was a remarkable machine. It contained a Z-80A processor running at 3.5 MHz and 8K of ROM including a built in BASIC. On the left side of the computer are 4 ports. The first from the rear to front is a standard RCA type plug output from the built in RF modulator to a standard TV. Curiously the original mail order units from Sinclair output to a UHF channel not the usual VHF channel 3 or 4 that is seen on most all consumer video products sold in the US. This was changed when Timex started selling the computer under its own logo and the later ZX-81's all included a channel 3/4 switch on their underside. The next two ports are 8mm mini jacks for input and output to a standard cassette recorder for storing the programs to and from the computer. The process of loading a program into the computer was a difficult and slow process. As it was with most of the computers of that era that used a cassette as a mass storage device. The cassette recorder was generally slow and unreliable and greatly dependent on a number of factors such as the volume the recorder is set at to record or playback a program. The last port is an 8mm mini jack for the supplied 9 VDC power supply. The ZX-81 comes packaged with a very good owners manual with a very informative BASIC tutorial that takes the first time user step by step through the many features and uses of the ZX-81. All this was sold at $79.95 for the basic unit in kit form and $99.95 fully assembled and tested when equivalent machines at that time were selling at 6 times the cost. Although the basic unit was sold with only 1K of RAM an optional 16K RAM module was available for $49.95.

      This was my first computer. I bought this one in kit form on June 5,1982 along with a 16k RAM module. I had been interested in computers for a number of years prior to purchasing this one and had read a lot of books and magazines about them. I wrote my first BASIC program on it, a program to balance my checkbook. 

      I used a Radio Shack cassette tape recorder as the mass storage device and had the ZX-81 hooked to a Sears 12" Black and White TV. 

System Architecture

Memory

Standard Features

Disk Storage

Video & Graphics

Sound