7 Developer : Sinclair Research Manufacturer : Timex Corporation Year of Release : 1981 Units sold : 1.5 million CPU : Z80 at 3.25 MHz Memory : 1 KB (64 KB max. 56 KB usable) Storage : External cassette tape recorder at 250 baud Display : Monochrome display on UHF television Graphics : 24 lines x 32 characters or 64 x 48 pixels graphics mode