ZX80
It all started in January 1980 when Sinclair announced the project that their engineers had been working on since May the previous year. The following month the ZX80 appeared, in kit form initially, followed quickly by a prebuilt (slightly more expensive) version. The Z80 went on to sell over 50,000 units - the seeds of the home computer revolution in the UK had been sewn.

ZX81
In March 1981 the follow up in the form of the ZX81 was launched and after a “buggy” start, its success snowballed as the bedroom programming revolution started and magazines sprung up to cater for the demand for program listings!

 As more and more commercial games appeared (some very successful if your imagination could stretch to the blocky graphics looking like aliens), sales rocketed and within 2 years over a million ZX81’s had been sold.

ZX Spectrum
The pinnacle of Sir Clive's creations was the Spectrum - arriving in 1982 it brought colour computing to the masses.

Very clever marketing stressing the educational capabilities of the computer and software that would follow, enabled millions of school kids to convince their parents that it was a homework tool!
The difficulty Sinclair had in meeting those initial demands is now stuff of legend.

Masses of software (mainly games despite the marketing) and add on peripherals appeared rapidly and third party manufacturers of many types flourished.

Sinclair was on a roll...

Spectrum+
In October 1984 the Spectrum+ appeared. Essentially the same machine, but with a keyboard where the keys actually moved! For the rubber key purists though, finding all those keywords proved much more difficult without the colour coding. 

By 1985 though sales had started to slide and work began to improve the Spectrum+ paving the way for the new Spectrum 128.

Spectrum+ 128
The new machine was the first Spectrum to produce decent sound via its new 3 channel 7 octave dedicated sound chip system.
It also sported 128K RAM and a new 128 Basic which saw off the old keyword entry (although 48K compatibility mode was retained for all that software out there).

 The new machine was launched in February 1986 - just a little too late for the struggling Sinclair.

Amstrad bought the company a few months later after Sinclair  had suffered heavy financial losses (blamed on the Sinclair C5 pedal car) and promptly dropped the Spectrum 128 making it somewhat of a valuable rarity today.

Spectrum +2
Later the same year Amstrad brought the first version of the Spectrum +2 to market which was Spectrum 128 board squeezed into case of similar design to its own CPC 464.

It had a built in tape recorder and was aimed more at the console market.

With Amstrad's greater emphasis on quality, the machine was much better built and so much more reliable than earlier Sinclair built spectrum models.

Spectrum +3
Development of the spectrum range was now at a much slower pace and the next machine - the Spectrum +3 - didn’t appear until 1987.

This had Amstrad's own 3” disk drive from the CPC6128  built in and an upgraded version of BASIC, complete with a new operating system.

 The new model didn’t sell well though and the +2 remained the punters choice of machine.

It was difficult to get software for the +3 and most disk based games were existing 48K games adjusted to load from, and save to, disk. 
It was even more difficult to transfer tape based games to disk.

Spectrum +2A
It was probably the shortage of dedicated 128K disk based software for the Spectrum +3, coupled with difficulties of transferring cassette based software to disk that an updated version of the +2, the +2A, also appeared later in 1987.

The main board and ROMs were virtually identical to the +3 and it continued selling well beyond the +3 sales into the early 1990's.

Due to it being based on the +3, It wasn't as compatible with the back list of 48K and 128K cassette software as the first Spectrum +2 (grey model), but the better ROM and cassette reliability helped to make up for that.

Sinclair QL
Alongside of all this Spectrum activity, Sinclair got serious in 1984 and launched the Sinclair QL in January of that year.
It was described as the first 32-bit business machine for under £40.

With a new Motorola 68008 processor, 128K RAM (although strangled by an 8-bit bus), twin microdrives and real monitor connectivity it certainly sounded impressive.

However, real supply problems from a disastrous mail order arm, the rapid growth of the PC and the damage to the Sinclair name done by the C5 Trike saw sales struggle to only 100,000 units by the time Amstrad bought the company. Sales struggled on to around 150,000 units before it was dropped.

 Still popular today with collectors though, particularly good quality boxed systems.