Changes

* 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 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 it's 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+: 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 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.