{"id":21564,"date":"2025-07-08T12:12:04","date_gmt":"2025-07-08T16:12:04","guid":{"rendered":"https:\/\/carleton.ca\/scs\/?page_id=21564"},"modified":"2025-07-15T14:18:45","modified_gmt":"2025-07-15T18:18:45","slug":"vin72","status":"publish","type":"page","link":"https:\/\/carleton.ca\/scs\/vintage-computing\/item\/vin72\/","title":{"rendered":"Sinclair ZX-81"},"content":{"rendered":"<h2>Sinclair ZX-81 (Timex Sinclair 1000)<\/h2>\n<p>[Vin72]<\/p>\n<p>The Sinclair ZX-81, introduced in 1981, was a groundbreaking home computer celebrated for its ultra-affordable price, minimalist design with only four main chips, and a base of just 1 KB of RAM\u2014features that made personal computing accessible to millions. Its claim to fame was democratizing computer ownership: it sold over 1.5 million units worldwide, sparked a home computing boom, and inspired a generation of programmers and hobbyists by making programming and computing available to the general public through high street retailers rather than just mail order.<a href=\"https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250708_163850338-scaled.jpg\"><img decoding=\"async\" loading=\"lazy\" class=\"alignright size-large wp-image-21573\" src=\"https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250708_163850338-400x300.jpg\" alt=\"Timex Sinclair ZX-81\" width=\"400\" height=\"300\" srcset=\"https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250708_163850338-400x300.jpg 400w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250708_163850338-240x180.jpg 240w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250708_163850338-160x120.jpg 160w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250708_163850338-768x577.jpg 768w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250708_163850338-1536x1153.jpg 1536w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250708_163850338-2048x1538.jpg 2048w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250708_163850338-800x600.jpg 800w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250708_163850338-360x270.jpg 360w\" sizes=\"(max-width: 400px) 100vw, 400px\" \/><\/a><\/p>\n<p>The ZX-81 was especially significant in computing history for catalyzing the mass adoption of home computers in the UK and North America, including Canada, where it was sold as the <a href=\"https:\/\/carleton.ca\/scs\/vintage-computing\/item\/vin53\/\">Timex Sinclair 1000<\/a>\u00a0one of the first widely available home computers in the Canadian market, manufactured by Timex Corporation in Dundee, Scotland. Its simplicity, affordability, and broad reach played a pivotal role in shaping the early home computing landscape and nurturing the software and hardware industries that followed.<\/p>\n<ul>\n<li><strong>Manufacturer<\/strong>: Sinclair Research<\/li>\n<li><strong>Released<\/strong>: 1981<\/li>\n<li><strong>Type<\/strong>: Home Computer<\/li>\n<li><strong>Cost at release<\/strong>: GBP \u00a399.95 (CAD ~$745 adjusted for inflation)<\/li>\n<li><strong>MIPS<\/strong>: 0.058 (58 KIPS)<\/li>\n<\/ul>\n<h3><span class=\"NormalTextRun SCXW169789978 BCX0\">Hardware Specifications<\/span><\/h3>\n<ul>\n<li><strong>CPU<\/strong>: Zilog Z80A, 8-bit, running at 3.25 MHz.<\/li>\n<li><strong>Memory<\/strong>:\n<ul>\n<li>RAM: 1 KB built-in (expandable up to 16 KB or more via external modules; max 56 KB usable).<\/li>\n<li>ROM: 8 KB, containing Sinclair BASIC interpreter.<\/li>\n<\/ul>\n<\/li>\n<li><strong>Display<\/strong>:\n<ul>\n<li>Text Mode: 32 characters x 24 lines (2 lines reserved for system use).<\/li>\n<li>Graphics Mode: 64 x 44 pixels (monochrome).<\/li>\n<\/ul>\n<\/li>\n<li><strong>Keyboard<\/strong>: 40-key membrane, pressure-pad switches.<\/li>\n<li><strong>Video Output<\/strong>: RF modulator for connection to a standard TV (UHF\/NTSC\/PAL, depending on region).<\/li>\n<li><strong>Sound<\/strong>: None.<\/li>\n<li><strong>I\/O Ports<\/strong>: Edge connector for RAM expansion and peripherals, cassette interface for data storage (audio cassette, 250 baud).<\/li>\n<li><strong>Power Supply<\/strong>: 9V DC, 600 mA (center positive).<\/li>\n<li><strong>Case Dimensions<\/strong>: Approx. 167 mm (width) x 175 mm (depth) x 40 mm (height).<\/li>\n<li><strong>Weight<\/strong>: 350 grams (12.15 oz)<\/li>\n<\/ul>\n<h3><span class=\"TextRun SCXW50331614 BCX0\" lang=\"EN-US\" xml:lang=\"EN-US\" data-contrast=\"auto\"><span class=\"NormalTextRun SCXW50331614 BCX0\">Operating System &amp; Programming Languages<\/span><\/span><span class=\"EOP SCXW50331614 BCX0\" data-ccp-props=\"{&quot;335559685&quot;:0}\">\u00a0<\/span><\/h3>\n<ul>\n<li><strong>Operating System<\/strong>: used an 8 KB ROM containing its operating system and the built-in Sinclair BASIC interpreter. The operating system was tightly integrated with BASIC, providing the user interface, program editing, and system control directly through the BASIC environment<\/li>\n<li><strong>Programming Languages<\/strong>:\n<ul>\n<li>Sinclair ZX81 BASIC: The default and primary language, resident in ROM, was a minimal but functional dialect of BASIC designed for ease of use and learning.<\/li>\n<li>Z80 Assembly Language \/ Machine Code: Advanced users could write programs directly in Z80 assembly or machine code, either by embedding code within BASIC programs (using the USR function) or by loading binary files via cassette.<\/li>\n<li>Forth: Several Forth implementations (such as fig-FORTH and ZX-FORTH) were available through third-party expansion cartridges or software.<\/li>\n<li>Pascal: Pascal interpreters and compilers were produced by third parties, allowing structured programming on the ZX-81\/Timex Sinclair 1000.<\/li>\n<li>BCPL: Some add-ons enabled use of this early systems programming language.<\/li>\n<li>Other Languages: Additional niche and experimental languages, such as RPNZL (a Forth-like language), and extended versions of BASIC with added commands, were also available through software expansions and magazines.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<h3>Notables<a href=\"https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250715_181445338-scaled.jpg\"><img decoding=\"async\" loading=\"lazy\" class=\"alignright size-large wp-image-21730\" src=\"https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250715_181445338-400x300.jpg\" alt=\"Timex Sinclair 1000\" width=\"400\" height=\"300\" srcset=\"https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250715_181445338-400x300.jpg 400w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250715_181445338-240x180.jpg 240w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250715_181445338-160x120.jpg 160w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250715_181445338-768x577.jpg 768w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250715_181445338-1536x1153.jpg 1536w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250715_181445338-2048x1538.jpg 2048w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250715_181445338-800x600.jpg 800w, https:\/\/carleton.ca\/scs\/wp-content\/uploads\/PXL_20250715_181445338-360x270.jpg 360w\" sizes=\"(max-width: 400px) 100vw, 400px\" \/><\/a><\/h3>\n<ul>\n<li>Democratized Home Computing: One of the first truly affordable, mass-market home computers, selling over 1.5 million units globally.<\/li>\n<li>Catalyst for Industry: Sparked a wave of software and hardware companies and inspired a generation of programmers and engineers.<\/li>\n<li>Retail Revolution: First home computer widely available in high street shops, not just by mail order<\/li>\n<li>Minimalist Marvel: Used only four main chips, drastically reducing cost and complexity compared to competitors.<\/li>\n<li>\u201cWobble RAM\u201d: The 16KB RAM expansion was infamous for being unstable\u2014any bump could crash the computer and erase all data, earning the nickname \u201cwobble RAM\u201d among users.<\/li>\n<li>Keyboard Quirk: Featured a pressure-sensitive membrane keyboard, often compared to microwave oven buttons\u2014cheap, but challenging for extended typing.<\/li>\n<li>Legendary 1K Chess: Despite only 1 KB of RAM, programmers managed to create games like 1K ZX Chess, fitting most chess rules in just 672 bytes.<\/li>\n<li>Square Root Bug: Early models had a notorious bug where the square root of 0.25 returned the wrong result (1.359&#8230;), prompting Sinclair to replace faulty ROMs.<\/li>\n<li>\u201cDogsbody\u201d Chip: The ULA chip was nicknamed the \u201cdogsbody\u201d for handling multiple vital tasks usually spread across several chips.<\/li>\n<li>First Computer for Many: For countless users in the UK, U.S., and Canada, the ZX-81 (Timex Sinclair 1000) was their first computer experience.<\/li>\n<\/ul>\n<p><\/p>\n<p><strong>Donated By<\/strong>: Don Shesnicky and Arlen Michaels<\/p>\n<p><\/p>\n","protected":false},"excerpt":{"rendered":"<p>Sinclair ZX-81 (Timex Sinclair 1000) [Vin72] The Sinclair ZX-81, introduced in 1981, was a groundbreaking home computer celebrated for its ultra-affordable price, minimalist design with only four main chips, and a base of just 1 KB of RAM\u2014features that made personal computing accessible to millions. Its claim to fame was democratizing computer ownership: it sold [&hellip;]<\/p>\n","protected":false},"author":7,"featured_media":0,"parent":19704,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_relevanssi_hide_post":"","_relevanssi_hide_content":"","_relevanssi_pin_for_all":"","_relevanssi_pin_keywords":"","_relevanssi_unpin_keywords":"","_relevanssi_related_keywords":"","_relevanssi_related_include_ids":"","_relevanssi_related_exclude_ids":"","_relevanssi_related_no_append":"","_relevanssi_related_not_related":"","_relevanssi_related_posts":"","_relevanssi_noindex_reason":"","_mi_skip_tracking":false,"_exactmetrics_sitenote_active":false,"_exactmetrics_sitenote_note":"","_exactmetrics_sitenote_category":0,"footnotes":"","_links_to":"","_links_to_target":""},"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v21.2 - https:\/\/yoast.com\/wordpress\/plugins\/seo\/ -->\n<title>Sinclair ZX-81 - School of Computer Science<\/title>\n<meta name=\"description\" content=\"Sinclair ZX-81 (Timex Sinclair 1000) The Sinclair ZX-81, introduced in 1981, was a groundbreaking home computer celebrated for its ultra-affordable price,\" \/>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/carleton.ca\/scs\/vintage-computing\/item\/vin72\/\" \/>\n<meta name=\"twitter:label1\" content=\"Est. reading time\" \/>\n\t<meta name=\"twitter:data1\" content=\"4 minutes\" \/>\n<script type=\"application\/ld+json\" class=\"yoast-schema-graph\">{\"@context\":\"https:\/\/schema.org\",\"@graph\":[{\"@type\":\"WebPage\",\"@id\":\"https:\/\/carleton.ca\/scs\/vintage-computing\/item\/vin72\/\",\"url\":\"https:\/\/carleton.ca\/scs\/vintage-computing\/item\/vin72\/\",\"name\":\"Sinclair ZX-81 - 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