It is based around the Zilog Z80 CPU clocked at 3.5Mhz, which was initially developed for pocket calculators, where Sir Clive Sinclair had originally begun his entry into mass market electronics. The Z80 is still in production, and remains used in many scientific and graphical calculators. The use of this CPU allowed both he ZX81 and the Spectrum successors to undercut other brands on price in the fiercely competitive 80's home computer market. All Spectrums use the CP/M operating system.
There was a whole generation of Spectrum class computers, though all shared the low-cost philosophy.
- Spectrum 16k/48k: The main model, with a small case and rubber keyboard and RF output only, and choice of 16k or 48k models. Aside from the ZX81, they were amongst the cheapest turn-key home computers available in the UK.
- Spectrum+: Essentially a 48k with improved keyboard and a bigger, stronger external case. Apart from a reset button, it is identical to the 48k in terms of electronics. Soon after its release, it outsold the basic model by a 2:1 ratio, despite retailing for around £25 more. It was possible to buy a kit to convert an existing 48k to the "+" specification, which was easy to perform since no modification of the motherboard was needed.
- Spectrum 128k: A joint venture with a Spanish company (Investronica), where Sinclair had always had an important market, this was the first spectrum to support the Spanish character set and OS. The joint venture also dramatically updated the basic design of the Spectrum, introducing a modern sound chip with MIDI support (the Yamaha/General Instruments AY-3-8910, as used on the Atari ST, Apple II, and most other computers of the era), RGB monitor output, serial port and a much larger 32kb ROM with improved BASIC that also took advantage of the new features. An external numeric keypad was also available in Spain. This would be the last major development of the basic Spectrum design, and soon after, a financially struggling Sinclair Research was purchased by Amstrad for just £5 million.
- Spectrum +2: A cost reduced version of the 128k with a built in tape deck, still a common external data storage medium at the time for home computers. The keyboard from the Amstrad CPC range was also used instead of the previous Sinclair design. Came in a grey case, rather than the normal Sinclair black.
- Spectrum +3: As above but with an unusual 3" disk drive format, as used by Amstrad on the CPC and PCW range of computers instead of the tape deck, and in a black case.
Sinclair Research originally provided a wide array of external devices for the Spectrum, especially since many models lacked the standard I/O ports. These included a miniscule thermal printer, network adapter and external high speed tape drives. In addition 3rd party manufacturers made numerous other devices and port adapters to allow use of disk drives, printers etc.
The Spectrum is widely and fondly remembered in Britain by those who grew up in the 1980s, and many of the games developed for the system by home programmers paved the way for many of the leading European software houses of today. It also taught a generation the basics of computer science and programming, due to the popularity of "program your own game" articles in Spectrum fan magazines, as well as numerous contests. In addition due to the limited functionality of the basic machine, many users "hacked" their computer to add additional functionality.
Soviet and Eastern Bloc Clones
Spectrum compatible machines were widely produced in the Eastern Bloc and Soviet Union up until the mid 1990s. They were produced by various different enterprises, often only semi-officially. The clones served in a much wider variety of uses than in Europe, and were used in schools and other institutions as well as for home use, and as such some were considerably more advanced than the basic low-cost models in Europe, including models clocked at up to 25Mhz. Due to this several attempts were made to import them once the iron curtain came down, as they had considerable appeal to hardware enthusiasts who did not want to abandon the Spectrum platform for the "conformity" of the PC. However, copyright issues prevented this.