Sinclair ZX80 - 1980
At £99.95 ready assembled (or £79.95 if you felt confident enough to solder it together yourself) then it fulfilled the first aim of being under £100. It displayed via a normal television showing 24 lines of 32 characters (more on the screen in a while). It had 1KB (1000 bytes) of memory but came with BASIC so was MUCH easier to program on. The machine came with lots of foibles though:
1. Proper keyboards were expensive. To avoid this, the ZX80 came with the most awful "tough sensitive" keyboard. Sadly, it was anything BUT touch sensitive. It was basically two thin films held apart. When you pressed down a little then the films would touch and generate the relevant key press. It clicked a little like a real keyboard but typing had to slow and steady.
2. To avoid too much key entry, Sinclair adopted a keyword entry method. If you look at the photo then every key has a number of things around it. What you got depended on what you were typing. If you typed 1 then 0 for line 10, then pressing the K key actually showed LET (since LET starts with a K it is not easy to remember - an inconsistency made worse as the L key was not used for anything else). Some of the keys made a little more sense, N for NEXT, F for FOR etc. It even put a space at the end of the keyword for you. Pressing the SHIFT key and the K offered the + key. Look forward to the ZX Spectrum to see this key entry system taking to its (il)logical conclusion.
3. All computer screens need continually updating or whatever you printed on the screen would just disappear again. Modern computers (well, everything bar the ZX80 and very few others) have a second chip of some kind to handle the refresh. The ZX80 used the main processor to handle screen refresh so was then unable to do anything else. What this meant was that the screen went blank every time the computer had work to do and displayed when it was idle - normally when it was waiting for input. This is why all the early games were text based.
4. Most of you will have used a word processor such as Word. You can move around the text all over the screen and make whatever changes you want. Most early computers were not able to do this and had a number of ways to permit editing of lines of program. One computer, the Cambridge Z88, simply required you to retype the line! As usual, Sinclair had their own curious twist. The screen was effectively split into 22 lines at the top and 2 at the bottom. The cursor keys (above the 6 and 7 keys) permitted you to move up and down the lines on screen then pressing the enter key brought the marked line down to the bottom 2 lines where you could move around with the left and right arrow keys and delete and replace characters. It was not difficult to do but very unique to Sinclair.
5. Another distinction of the ZX80 (and ZX81 and Spectrum which followed) is that the screen was in white with black text. Most computers of their day had a black background with white (or green or amber) text which was far more restful on the eye.
6. It was possible to load and save programs onto a cassette recorder but only, it seemed, if there was an R in the month, it was sunny outside and the cow had recently jumped over the moon. Some cheap recorders were better than others and the record and playback volume was incredibly sensitive. This problem continued on the ZX81.
7. If a "massive" 1KB of memory was not enough then you could purchase an enormous 16KB expansion. This plugged into the end of the circuit board and hung off the back. Frequently, it would move slightly, crash the computer and you would lose hours of typing - Oh what fun we had!
8. The ROM was not big enough for everything so bits were left out. One very serious edition was the ability to use floating point numbers (e.g. 1.75, 236.654556). Integers are all well and good but of limited use for your physics homework!
Despite all of these problems, the ZX80 was a success. Around 50,000 were sold though when you think that most people had only ever dreamt of working on a computer (never mind owning their own) then it becomes understandable.