May 2, 2019

More ZX81 Thoughts

I've already described the first personal computer that I owned, the Sinclair ZX81, but I had some more memories to go with that post.

The amount of memory (RAM) that the computer had was 1K, that's 1,024 bytes of memory. Take out just over 100 bytes for system usage and you ended up with around 900 bytes of memory for your program and its data. My current desktop computer is about a million times more powerful than the ZX81 with its 24 Gb of memory but back then the few home computers available came with only a small amount of memory.

An additional memory pack was available for the ZX81. It was known as the Ram Pack and it brought the memory capacity up to 16K of RAM. Unfortunately, its connector was not very well designed and it literally just plugged straight into the edge of the circuit board inside the ZX81. The result was that it would wobble if you bumped the computer and would cause the computer to crash. Owners of Ram Packs tried many different ways to keep their computers from crashing. I had the most success with resting my computer on a small book to keep the Ram Pack in the air and prevent it flexing on the surface of my desk.

Without a disk drive, the way that you got programs into the computer was either by typing them in through the flat membrane keyboard or by playing recorded programs into its audio interface via a jack plug from a tape player. If you've ever heard the sounds a modem makes, that's what the programs sounded like. The programs were quite short, so it quickly became possible to buy C15 cassette tapes, that were just 15 minutes of total recording time, seven and a half minutes each side. I used to reuse the program tapes to record songs off of the radio during the chart countdown show on Sunday afternoons so I could listen to them during the week. Sometimes I would listen to the songs while going to bed and it was not unusual to be jolted at the end of a song by the screeching sound of a program that was on the tape before I recorded a song onto it.

Tags: Personal