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Depending on what tickles your fancy, there are rather a lot to choose from. And that's just the official Sinclair models and the official clones...
Sinclair's computers based on the Z80A microprocessor started with the ZX80. The ZX81 was next. Both only have 1K bytes of RAM. In the U.S.A. Sinclair also sold the U.S.A. version of the ZX81. But stopped after an agreement with Timex. Timex under the Timex Sinclair name sold the very similar TS1000. The TS1000 has 2K bytes of RAM.
In the U.K. Sinclair produced a colour computer called the ZX Spectrum. This came in two flavours: 16K bytes of RAM or 48K bytes of RAM.
The next model from Timex was the TS1500. Essentially a TS1000 in a ZX Spectrum case (with similar rubber keyboard) but with 16K bytes of RAM.
Eventually Timex designed their own new colour computer model. The TS2068 but it was not very successful.
In parts of Europe, such as Portugal, Timex Computer (a different division to the U.S.A. operation) sold the TC2068 and later on the TC2048.
Sinclair was working on their new computer, This was based on the Motorola 68008 16/32 bit microprocessor. The name was Quantum Leap, or QL for short.
Sinclair in the U.K. upgraded the ZX Spectrum, the new version was the ZX Spectrum+ with 48K bytes of RAM. It had a larger case with a better keyboard.
In Spain, a new model only for that market was launched with 128K bytes of RAM. It had better sound and more ports. Once Sinclair had shifted many of the ZX Spectrum+ stock, a revised 128K model was released in the U.K. Affectionately known as the "toastrack" because of the metal heatsink on the right hand side.
By now Timex had abandoned the computer market in the U.S.A.
Sinclair was in financial trouble. And ended up selling the computer business to Amstrad.
Amstrad were not interested in the QL. It was abandoned.
Amstrad went on to produce the ZX Spectrum+2 (in a grey case hence it's called the "+2 grey"), then a ZX Spectrum+3. They discontinued the ZX Spectrum+2 and replaced it with the ZX Spectrum+2 in a black case, but underneath it is called a +2A. The same case with a later PCB revision is called the +2B.
Sinclair set up a brand new company, This company only made and sold one computer model, the Cambridge Z88. A lightweight portable, a "laptop" for want of a better description. It had a LCD and ran from batteries. But it was not compatible with any of the earlier computers even though it has a Z80A microprocessor.
There is a modern computer called the ZX Spectrum Next. It's far more powerful but can run in a compatibility mode so can run ZX Spectrum software.
There are many, many other clones of both the ZX80, ZX81/TS1000 and ZX Spectrum (most being unofficial).
Mark