The ZX81 came with 1 kB of on-board memory that could officially be expanded externally to 16 kB. Its single circuit board is housed inside a wedge-shaped plastic case measuring 167 millimetres (6.6 in) deep by 40 millimetres (1.6 in) high. The memory is provided by either a single 4118 (1024 bit × 8) or two 2114 (1024 bit × 4) RAM chips. There are only three other chips on board: a 3.5 MHz Z80A 8-bit microprocessor from Nippon Electric (now NEC), an uncommitted logic array (ULA) chip from Ferranti and a 8 kB ROM providing a simple BASIC interpreter. The entire machine weighs just 350 grams (12 oz). Early versions of the external RAM cartridge contained 15 kB of memory using an assortment of memory chips, while later versions contained 16 kB of chips but the lowest addressed kilobyte was disabled.
ZX Spectrum 48K
(I had two)