The Sinclair ZX81 revolutionised home computing in the United Kingdom. A fully working computer for under £100.
With a huge amount of add-ons – such as Ram Packs and fully moving keyboards.

Technical Specifications
CPU : NEC Zilog Z80A compatible @ 3.25 MHz
ROM : 8 Kb (adapted from ZX80 Rom)
RAM : 1 Kb (expandable) to 16 KByte and further. Ours (here) has 64 Kb internally.
Display : Television
Text display : 32 x 22
Graphics display : 64 x 44
Colours : black and white only
Sound : No sound output at all
Keyboard : 40 key, with graphics and function modes, includes 20 graphical and 54 inverse video
Keyboard : characters Sinclair calls the keyboard a touch sensitive membrane.
Interface : Expansion Bus
Data Storage : Cassette Based via Earphone & Microphone 3.5mm Connection
Power Supply : External 9v DC power pack