{"id":320,"date":"2022-02-20T10:47:02","date_gmt":"2022-02-20T09:47:02","guid":{"rendered":"https:\/\/www.sinclaircollection.site\/?page_id=320"},"modified":"2025-09-09T09:35:27","modified_gmt":"2025-09-09T07:35:27","slug":"sinclair-zx81","status":"publish","type":"page","link":"https:\/\/www.sinclaircollection.site\/?page_id=320","title":{"rendered":"Sinclair ZX81"},"content":{"rendered":"\t\t<div data-elementor-type=\"wp-page\" data-elementor-id=\"320\" class=\"elementor elementor-320\">\n\t\t\t\t\t\t<section class=\"elementor-section elementor-top-section elementor-element elementor-element-03e23db elementor-section-boxed elementor-section-height-default elementor-section-height-default\" data-id=\"03e23db\" data-element_type=\"section\">\n\t\t\t\t\t\t<div class=\"elementor-container elementor-column-gap-default\">\n\t\t\t\t\t<div class=\"elementor-column elementor-col-100 elementor-top-column elementor-element elementor-element-f4eee05\" data-id=\"f4eee05\" data-element_type=\"column\">\n\t\t\t<div class=\"elementor-widget-wrap elementor-element-populated\">\n\t\t\t\t\t\t<section class=\"elementor-section elementor-inner-section elementor-element elementor-element-aeaf08c elementor-section-boxed elementor-section-height-default elementor-section-height-default\" data-id=\"aeaf08c\" data-element_type=\"section\">\n\t\t\t\t\t\t<div class=\"elementor-container elementor-column-gap-default\">\n\t\t\t\t\t<div class=\"elementor-column elementor-col-50 elementor-inner-column elementor-element elementor-element-6366198\" data-id=\"6366198\" data-element_type=\"column\">\n\t\t\t<div class=\"elementor-widget-wrap elementor-element-populated\">\n\t\t\t\t\t\t<div class=\"elementor-element elementor-element-ed3d4b4 elementor-widget elementor-widget-image\" data-id=\"ed3d4b4\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<style>\/*! elementor - v3.23.0 - 05-08-2024 *\/\n.elementor-widget-image{text-align:center}.elementor-widget-image a{display:inline-block}.elementor-widget-image a img[src$=\".svg\"]{width:48px}.elementor-widget-image img{vertical-align:middle;display:inline-block}<\/style>\t\t\t\t\t\t\t\t\t\t<img fetchpriority=\"high\" decoding=\"async\" width=\"768\" height=\"768\" src=\"https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/zx81-0-768x768.jpg\" class=\"attachment-medium_large size-medium_large wp-image-9261\" alt=\"\" srcset=\"https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/zx81-0-768x768.jpg 768w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/zx81-0-300x300.jpg 300w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/zx81-0-1024x1024.jpg 1024w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/zx81-0-150x150.jpg 150w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/zx81-0-1536x1536.jpg 1536w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/zx81-0-666x666.jpg 666w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/zx81-0-96x96.jpg 96w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/zx81-0.jpg 1594w\" sizes=\"(max-width: 768px) 100vw, 768px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t<div class=\"elementor-column elementor-col-50 elementor-inner-column elementor-element elementor-element-9405b4b\" data-id=\"9405b4b\" data-element_type=\"column\">\n\t\t\t<div class=\"elementor-widget-wrap elementor-element-populated\">\n\t\t\t\t\t\t<div class=\"elementor-element elementor-element-b94f498 elementor-widget elementor-widget-text-editor\" data-id=\"b94f498\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<style>\/*! elementor - v3.23.0 - 05-08-2024 *\/\n.elementor-widget-text-editor.elementor-drop-cap-view-stacked .elementor-drop-cap{background-color:#69727d;color:#fff}.elementor-widget-text-editor.elementor-drop-cap-view-framed .elementor-drop-cap{color:#69727d;border:3px solid;background-color:transparent}.elementor-widget-text-editor:not(.elementor-drop-cap-view-default) .elementor-drop-cap{margin-top:8px}.elementor-widget-text-editor:not(.elementor-drop-cap-view-default) .elementor-drop-cap-letter{width:1em;height:1em}.elementor-widget-text-editor .elementor-drop-cap{float:left;text-align:center;line-height:1;font-size:50px}.elementor-widget-text-editor .elementor-drop-cap-letter{display:inline-block}<\/style>\t\t\t\t<p>Brand:&nbsp;<strong>Sinclair Research Ltd.<br><\/strong>Model: <strong>ZX81<\/strong><br>Country of origin:&nbsp;<strong>United Kingdom<\/strong><br>Made in:&nbsp;Scotland (Dundee)<br>Manufacturer: <b>Timex Corp.<\/b><br>Launch date: <b>5 March&nbsp;<\/b><strong>1981<\/strong><br>Price in UK: <b>\u00a369.95 \/ \u00a349.95 (kit)<\/b><br>Price in NL: <b>\u0192 595,-<\/b> \/&nbsp;<b>\u0192 499,-<\/b> (7-&#8217;82)<br>Price in Fr: <b>580 F<\/b><\/p>\n<p>Board design: <b>Jim Westwood<br><\/b>ULA:&nbsp;<b>Brian Flint<\/b><br>Software:&nbsp;<b>Steve Vickers<\/b><br>Case design:&nbsp;<b>Rick Dickinson<br><\/b><\/p>\n<p>Dimensions:&nbsp;<span style=\"font-weight: bold;\">167 \u00d7 174 \u00d7 40 mm <\/span>(feet adds 2 mm)<br>Weight: <span style=\"font-weight: bold;\">340 g<\/span><b><br><\/b><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t<div class=\"elementor-element elementor-element-a6a6d2a elementor-widget elementor-widget-text-editor\" data-id=\"a6a6d2a\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p>This successor to the\u00a0<a href=\"https:\/\/www.sinclaircollection.site\/?page_id=320\"><u>ZX80<\/u><\/a>\u00a0reduced the chip count from 21 to only 4, by incorporating the Ferranti ULA, a &#8216;glue chip&#8217; and precursor of the modern day Gate Array IC.<\/p><p><i>(Text continues below the gallery)<\/i><\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-988cba8 elementor-widget elementor-widget-image-gallery\" data-id=\"988cba8\" data-element_type=\"widget\" data-widget_type=\"image-gallery.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t<style>\/*! elementor - v3.23.0 - 05-08-2024 *\/\n.elementor-image-gallery .gallery-item{display:inline-block;text-align:center;vertical-align:top;width:100%;max-width:100%;margin:0 auto}.elementor-image-gallery .gallery-item img{margin:0 auto}.elementor-image-gallery .gallery-item .gallery-caption{margin:0}.elementor-image-gallery figure img{display:block}.elementor-image-gallery figure figcaption{width:100%}.gallery-spacing-custom .elementor-image-gallery .gallery-icon{padding:0}@media 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src=\"https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2022\/02\/4_3_zx81-tv1-150x150.jpg\" class=\"attachment-thumbnail size-thumbnail\" alt=\"\" \/><\/a>\n\t\t\t<\/div><\/figure><figure class='gallery-item'>\n\t\t\t<div class='gallery-icon landscape'>\n\t\t\t\t<a data-elementor-open-lightbox=\"yes\" data-elementor-lightbox-slideshow=\"988cba8\" data-elementor-lightbox-title=\"My test card\" data-e-action-hash=\"#elementor-action%3Aaction%3Dlightbox%26settings%3DeyJpZCI6MTU2LCJ1cmwiOiJodHRwczpcL1wvd3d3LnNpbmNsYWlyY29sbGVjdGlvbi5zaXRlXC93cC1jb250ZW50XC91cGxvYWRzXC8yMDIyXC8wMlwvNF81XzAwLmpwZyIsInNsaWRlc2hvdyI6Ijk4OGNiYTgifQ%3D%3D\" href='https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2022\/02\/4_5_00.jpg'><img loading=\"lazy\" decoding=\"async\" width=\"150\" height=\"150\" src=\"https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2022\/02\/4_5_00-150x150.jpg\" class=\"attachment-thumbnail size-thumbnail\" alt=\"\" \/><\/a>\n\t\t\t<\/div><\/figure><figure 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https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/Photoroom-20240513_0438112-96x96.jpg 96w\" sizes=\"(max-width: 150px) 100vw, 150px\" \/><\/a>\n\t\t\t<\/div><\/figure><figure class='gallery-item'>\n\t\t\t<div class='gallery-icon landscape'>\n\t\t\t\t<a data-elementor-open-lightbox=\"yes\" data-elementor-lightbox-slideshow=\"988cba8\" data-elementor-lightbox-title=\"Advertisement\" data-e-action-hash=\"#elementor-action%3Aaction%3Dlightbox%26settings%3DeyJpZCI6MTU5LCJ1cmwiOiJodHRwczpcL1wvd3d3LnNpbmNsYWlyY29sbGVjdGlvbi5zaXRlXC93cC1jb250ZW50XC91cGxvYWRzXC8yMDIyXC8wMlwvNF8xMF96eDgxLmpwZyIsInNsaWRlc2hvdyI6Ijk4OGNiYTgifQ%3D%3D\" href='https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2022\/02\/4_10_zx81.jpg'><img loading=\"lazy\" decoding=\"async\" width=\"150\" height=\"150\" src=\"https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2022\/02\/4_10_zx81-150x150.jpg\" class=\"attachment-thumbnail size-thumbnail\" alt=\"\" \/><\/a>\n\t\t\t<\/div><\/figure>\n\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<section class=\"elementor-section elementor-inner-section elementor-element elementor-element-51de295 elementor-section-boxed elementor-section-height-default elementor-section-height-default\" data-id=\"51de295\" data-element_type=\"section\">\n\t\t\t\t\t\t<div class=\"elementor-container elementor-column-gap-no\">\n\t\t\t\t\t<div class=\"elementor-column elementor-col-50 elementor-inner-column elementor-element elementor-element-ca5b461\" data-id=\"ca5b461\" data-element_type=\"column\">\n\t\t\t<div class=\"elementor-widget-wrap elementor-element-populated\">\n\t\t\t\t\t\t<div class=\"elementor-element elementor-element-f1b7d86 elementor-widget elementor-widget-text-editor\" data-id=\"f1b7d86\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p>In January 1980, John Grant hired mathematician Steve Vickers to rewrite the ZX80 ROM for the ZX81, based on Grants earlier work. The commands DATA, READ and RESTORE were scrapped in favour of the <u><a href=\"https:\/\/www.sinclaircollection.site\/?page_id=528\">ZX Printer<\/a><\/u> commands LPRINT, LLIST and COPY.<\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t<div class=\"elementor-column elementor-col-50 elementor-inner-column elementor-element elementor-element-f4803cd\" data-id=\"f4803cd\" data-element_type=\"column\">\n\t\t\t<div class=\"elementor-widget-wrap elementor-element-populated\">\n\t\t\t\t\t\t<div class=\"elementor-element elementor-element-297a921 elementor-widget__width-initial elementor-widget elementor-widget-image\" data-id=\"297a921\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"920\" height=\"350\" src=\"https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/product-1152112.jpg\" class=\"attachment-large size-large wp-image-11488\" alt=\"\" srcset=\"https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/product-1152112.jpg 1000w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/product-1152112-300x114.jpg 300w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2024\/05\/product-1152112-768x292.jpg 768w\" sizes=\"(max-width: 920px) 100vw, 920px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-6fcee9f elementor-widget elementor-widget-text-editor\" data-id=\"6fcee9f\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p style=\"text-align: right;\">&#8220;ZX80 8K BASIC&#8221; prototype keyboard overlay with READ, RESTORE and DATA<\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t<div class=\"elementor-element elementor-element-a63df33 elementor-widget elementor-widget-text-editor\" data-id=\"a63df33\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p>Users could save themselves \u00a320 \/ $50 by building it from a\u00a0<a style=\"background-color: #c70101;\" href=\"https:\/\/www.sinclaircollection.site\/?page_id=7234\"><u>kit<\/u><\/a>.<\/p><p>ULA types <b>2C158E<\/b> and <b>2C184E<\/b> didn&#8217;t have a &#8216;back porch&#8217; giving a dark, blurry and noisy image, whereas ULA type <b>2C210E<\/b> did have a &#8216;back porch&#8217;, which improved compatibility with most TV&#8217;s. It is explained in\u00a0<a style=\"transition-property: all; background-color: #c70101;\" href=\"https:\/\/youtu.be\/1irH3KuGyl0\" target=\"_blank\" rel=\"noopener\"><u>this<\/u><\/a>\u00a0video.<\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<section class=\"elementor-section elementor-inner-section elementor-element elementor-element-9526735 elementor-section-boxed elementor-section-height-default elementor-section-height-default\" data-id=\"9526735\" data-element_type=\"section\">\n\t\t\t\t\t\t<div class=\"elementor-container elementor-column-gap-no\">\n\t\t\t\t\t<div class=\"elementor-column elementor-col-50 elementor-inner-column elementor-element elementor-element-c7d41c5\" data-id=\"c7d41c5\" data-element_type=\"column\">\n\t\t\t<div class=\"elementor-widget-wrap elementor-element-populated\">\n\t\t\t\t\t\t<div class=\"elementor-element elementor-element-f38ca75 elementor-widget elementor-widget-text-editor\" data-id=\"f38ca75\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p>There are 3 ROM types:<\/p>\n<p><b>550<\/b> &#8212; Initial ROM has the &#8216;square-root bug&#8217;: SQR 0.25 would return 1.3591409 instead of 0.5<\/p><p><b>622<\/b> &#8212; Fixed the math bug, added an extra CALL to clear the workspace in the INPUT routine and improved the syntax checking routine by testing bit 6 and 7 of system variable FLAGS.<br>It also introduced a new bug, explained in chapter 19 of the ZX81 programming manual:<\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-3f0dff7 elementor-widget elementor-widget-image\" data-id=\"3f0dff7\" data-element_type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"920\" height=\"119\" src=\"https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2025\/06\/20250609_1410234802-1024x133.jpg\" class=\"attachment-large size-large wp-image-13143\" alt=\"\" srcset=\"https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2025\/06\/20250609_1410234802-1024x133.jpg 1024w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2025\/06\/20250609_1410234802-300x39.jpg 300w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2025\/06\/20250609_1410234802-768x100.jpg 768w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2025\/06\/20250609_1410234802-1536x200.jpg 1536w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2025\/06\/20250609_1410234802-2048x267.jpg 2048w\" sizes=\"(max-width: 920px) 100vw, 920px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-3af90e5 elementor-widget elementor-widget-text-editor\" data-id=\"3af90e5\" data-element_type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<p>(memory address 16437 is system variable FRAMES_hi)<\/p><p><span style=\"font-weight: bold;\">649<\/span>&nbsp;&#8212; Final ROM which fixed the PAUSE statement bug<\/p>\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t<div class=\"elementor-column elementor-col-50 elementor-inner-column elementor-element elementor-element-2294066\" data-id=\"2294066\" data-element_type=\"column\">\n\t\t\t<div class=\"elementor-widget-wrap elementor-element-populated\">\n\t\t\t\t\t\t<div class=\"elementor-element elementor-element-e8e3745 elementor-absolute elementor-widget elementor-widget-image\" data-id=\"e8e3745\" data-element_type=\"widget\" data-settings=\"{&quot;_position&quot;:&quot;absolute&quot;}\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t<img loading=\"lazy\" decoding=\"async\" width=\"403\" height=\"194\" src=\"https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2025\/06\/622.jpg\" class=\"attachment-large size-large wp-image-13122\" alt=\"\" srcset=\"https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2025\/06\/622.jpg 403w, https:\/\/www.sinclaircollection.site\/wp-content\/uploads\/2025\/06\/622-300x144.jpg 300w\" sizes=\"(max-width: 403px) 100vw, 403px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t<\/div>\n\t\t","protected":false},"excerpt":{"rendered":"<p>Brand:&nbsp;Sinclair Research Ltd.Model: ZX81Country of origin:&nbsp;United KingdomMade in:&nbsp;Scotland (Dundee)Manufacturer: Timex<\/p>\n<p><span class=\"more-link\"><a href=\"https:\/\/www.sinclaircollection.site\/?page_id=320\" class=\"readmore\">Continue reading<span class=\"screen-reader-text\">Sinclair ZX81<\/span><\/a><\/span><\/p>\n","protected":false},"author":1,"featured_media":0,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"footnotes":""},"class_list":["post-320","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/www.sinclaircollection.site\/index.php?rest_route=\/wp\/v2\/pages\/320","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.sinclaircollection.site\/index.php?rest_route=\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/www.sinclaircollection.site\/index.php?rest_route=\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/www.sinclaircollection.site\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.sinclaircollection.site\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=320"}],"version-history":[{"count":151,"href":"https:\/\/www.sinclaircollection.site\/index.php?rest_route=\/wp\/v2\/pages\/320\/revisions"}],"predecessor-version":[{"id":13283,"href":"https:\/\/www.sinclaircollection.site\/index.php?rest_route=\/wp\/v2\/pages\/320\/revisions\/13283"}],"wp:attachment":[{"href":"https:\/\/www.sinclaircollection.site\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=320"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}