The Spectrum was the ZX81's colourful successor: a small black case with grey rubber keys and a rainbow stripe across one corner. Each key carried up to five commands, as BASIC keywords were typed with one press.
It was cheap, sold in the millions and became the heart of the British bedroom programming boom. Games loaded from cassette, with the famous screeching tones and stripy border.
Fifteen colours: eight in normal and bright versions, with black the same in both. The pixels were one colour each, but colour was stored per 8x8 square, with one ink and one paper colour in each. When two coloured things met in a square, one took on the other's colour. This was "colour clash", and it is why so many Spectrum games were drawn in one colour on black.
A one-bit beeper: the processor clicked a speaker on and off itself. It played one note at a time, and the game stopped while it played, unless a clever programmer wove the clicks into the rest of the code.