The Sinclair ZX81 is a home computer released in the United Kingdom in 1981 by Sinclair Research Ltd. It featured 1K of RAM that could be expanded to 64K, plus a flat membrane-type keyboard where commands could be entered in as single keystrokes. It ran Sinclair BASIC as its main operating system. It was released in America as the Timex-Sinclair 1000 (which featured 2K of RAM) and the Timex-Sinclair 1500 (with 16K RAM). Games that were made for this system were either on cassette or type-in creations of hobbyists found in various books. It was replaced by the ZX Spectrum in 1982.