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Timex Sinclair ZX-81

[Vin52]

The Timex Sinclair ZX-81 was a groundbreaking, ultra-affordable home computer introduced in 1981, notable for its minimalist design using only four main chips, a 3.5 MHz Z80A processor, and just 1 KB of RAM (expandable to 56 KB). Its claim to fame was making personal computing accessible to the masses with a retail price under $100, selling over 1.5 million units worldwide and inspiring a generation of programmers and hobbyists. Manufactured in Dundee, Scotland, by Timex Corporation—including for the Canadian market—the ZX-81 was sold in North America as the Timex Sinclair 1000, making it one of the first widely available home computers in Canada and cementing its importance in computing history.

• Manufacturer: Developed by Sinclair Research and manufactured by Timex Corporation at their Dundee, Scotland plant
• Type: Home computer
• Release Date: March 1981 (UK), July 1982 (North America)
• Cost at release: USD $99.95(CAD ~$360 adjusted for inflation)
• MIPS: 0.058  (58 KIPS) – theoretical max but ran much slower

Technical Specifications

• CPU: Zilog Z80A CPU running at 3.25 MHz
• RAM: 2 KB RAM (expandable to 16 KB with external module)
• ROM: 8 KB ROM with Sinclair BASIC interpreter
• Display: RF modulator for connection to standard TV, monochrome display (32 characters × 24 lines)
• Storage: Programs and data saved/loaded via standard cassette tape recorder
• Power: External 9V DC adapter

Operating System & Programming Languages 

• Operating System: Sinclair BASIC

• Supported Languages:
  • Z80 assembly language/machine code
  • Forth (including fig-FORTH and ZX-FORTH)
  • Pascal (via third-party add-ons)
  • BASIC compilers and assemblers
  • BCPL (with add-ons)
  • RPNZL (a FORTH-like language)
  • Extended BASIC (with additional commands)

Notables

• Minimalist Marvel: The ZX-81 was famously designed with only four main chips, drastically reducing cost and complexity compared to competitors that used dozens of chips.
• “Wobble RAM”: The 16KB RAM expansion pack was notorious for being unstable—any bump could cause the computer to crash and lose all data, earning it the nickname “wobble RAM” among users.
• Nicknames: In the U.S. and Canada, it was known as the Timex Sinclair 1000; in the UK, simply the ZX81. Some enthusiasts affectionately called it “the people’s computer” or “the £50 computer”.
• Keyboard Quirks: Its pressure-sensitive membrane keyboard was compared to a microwave oven’s buttons—cheap, but difficult to use for extended typing.
• Pop Culture: The ZX81’s limitations and quirks became part of its legend—its BASIC was so minimal that even the square root function was buggy in early ROMs.
• First for Many: For countless users in the UK, U.S., and Canada, the ZX81/Timex Sinclair 1000 was their first computer and introduction to programming, often via magazine-printed BASIC listings.
• Place in History: The ZX81 was one of the first truly affordable, mass-market home computers, selling over 1.5 million units globally and opening up computing to the general public. Its success paved the way for the ZX Spectrum and the democratization of home computing

Donated by: Arlen Michaels