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The Secret Chip That Made the ZX Spectrum Possible

The film's page has its chapters, every source, the code and the full transcript: The Secret Chip That Made the ZX Spectrum Possible.

Sources and credits for the film. Every fact in the narration is tied to a quotation from a captured source; every image, clip and piece of music is listed with its licence and where it came from. Archive images and footage are public domain, openly licensed or used for commentary, criticism and historical analysis. Maps, charts and diagrams were made for this film from the cited sources.

Images and footage (51)

  • Steve Vickers at TNMOC's 40th-anniversary Q&A describing how he joined the ZX81/Spectrum ROM project via Nine Tiles Information Handling and John Grant
    The National Museum of Computing. Fair-use candidate (copyright The National Museum of Computing / event participants). Source
  • check frame for clean-crop verification
    Silicon Dream 2013 / Chris Smith. Fair-use candidate (copyright Silicon Dream / Chris Smith). Source
  • Chris Smith showing his hand-rebuilt ZX Spectrum ULA, reverse-engineered from decapped die photographs, at Silicon Dream 2013
    Silicon Dream 2013 / Chris Smith. Fair-use candidate (copyright Silicon Dream / Chris Smith). Source
  • Sir Clive Sinclair photographed in 1990 (18 July) riding a prototype folding bicycle (the X-Bike, designed by Mark Sanders), a clear, identified photograph of Sinclair himself, though unrelated to the Spectrum; useful only for his likeness.
    Mark Sanders / Wikimedia Commons / CC BY-SA 4.0. CC BY-SA 4.0. Source
  • A video essay explaining the ZX Spectrum's colour clash / attribute clash limitation with named game examples
    YouTube uploader (commentary with game footage). Fair-use candidate (copyright uploader, commentary with game footage). Source
  • Rick Dickinson speaking to camera in his garden about the Spectrum's design
    BBC Arts / Centre for Computing History. Fair-use candidate (copyright BBC Arts / Centre for Computing History). Source
  • A 48K Spectrum (emulated) with a blank screen and black border, its speaker playing our own beeper program: a plain tone of about 430 Hz for 1.5 seconds, then a two-voice tune (Frere Jacques, traditional, over a bass line) made by switching one speaker bit between two square waves; the sound is the point, the picture is the machine at rest
    Retro Computer TV. Own work.
  • A 48K Spectrum (emulated) running our own border-stripe loop from contended memory (0x6000): blue and red stripes, even above the picture, stretched taller beside the picture while the ULA fetches the screen, running on into the bottom border
    Retro Computer TV. Own work.
  • Our two emulated 48K recordings side by side, captioned '0x6000 · SHARED LOWER MEMORY' (left) and '0x8000 · UPPER MEMORY' (right): the same border-stripe loop; on the left the blue and red stripes stretch beside the picture and run into the bottom border, on the right they stay even and finish two thirds of the way down
    Retro Computer TV. Own work.
  • A 48K Spectrum (emulated) loading our own tape at real speed: red and cyan pilot stripes, the header's 'Program: retrotech', blue and yellow data stripes, then a loading screen drawn in memory order (the top third first, line by line in the interleaved order, black on white), its colours arriving last, then a black border; with the tape's own sound
    Retro Computer TV. Own work.
  • Macro footage of a stage in Ferranti's semiconductor fabrication process (a wafer or die under process lighting) at the Gem Mill plant
    Ferranti / Martin Mallinson. Fair-use candidate (copyright Ferranti/successors; re-uploaded by former Ferranti engineer Martin Mallinson). Source
  • Tim Follin's five-channel Agent X title music from a real 48K Spectrum's beeper, heard over the uploader's presentation (the loading screen framed, a caption bar, a portrait of Follin): use for its sound, not as a picture of the game
    Fair-use candidate (copyright Beyond Software / Tim Follin). Source
  • Knight Lore (1984): a room rendered entirely in yellow ink on black, the same monochrome-per-room technique (and a room transition) seen throughout the game
    Fair-use candidate (copyright Ultimate Play The Game / Rare). Source
  • Lightforce (1986): the player's ship scrolling over a jungle river, green trees and cyan water each occupying their own attribute cells without visible colour clash
    Fair-use candidate (copyright FTL). Source
  • Popeye (1985): Popeye grappling with a large pink character sprite (Bluto) at the house door, both oversized relative to typical Spectrum platform-game sprites
    Fair-use candidate (copyright DKTronics / King Features Syndicate). Source
  • A ZX Spectrum Next (FPGA-based recreation of the Spectrum) running its own NextZXOS file browser, real hardware
    Fair-use candidate (copyright uploader / Spectrum Next demo). Source
  • A ZX Spectrum loading Jetpac from tape (an emulator or direct capture, not a camera on a television): red/cyan pilot-tone border stripes, then blue/yellow data stripes, with the header and the screen building up
    Fair-use candidate (copyright uploader / game copyright holder). Source
  • The completed Jetpac loading screen (an emulator or direct capture): the full-colour title, the astronaut and the Ultimate Play The Game logo, fully drawn in
    Fair-use candidate (copyright uploader / game copyright holder). Source
  • A hobbyist installing and testing a 'NebULA' modern replacement ULA chip in a real 48K ZX Spectrum
    16BitBench (YouTube). Fair-use candidate (copyright uploader, own repair footage). Source
  • Sidewize (Odin Computer Graphics/Firebird, 1987) gameplay, likely captured via emulator with a modern review overlay rather than filmed off real hardware; shows the game's horizontally-scrolling raster-timed display that the floating-bus claims discuss
    YouTube uploader. Fair-use candidate (copyright Odin Computer Graphics/Firebird Software). Source
  • A UK TV advert for the Sinclair ZX Spectrum
    Sinclair Research. Fair-use candidate (copyright Sinclair Research/successors). Source
  • A ZX Spectrum with its cassette-tape software collection fanned out in front of it, next to its own boxed manuals, a period photograph of the machine with its tape library, dated 1982.
    Museum Rotterdam / Wikimedia Commons / CC BY-SA 3.0. CC BY-SA 3.0. Source
  • A ZX Spectrum 48K with its rubber keyboard, photographed on a white background
    Bill Bertram / Wikimedia Commons / CC BY-SA 2.5. CC BY-SA 2.5. Source
  • A period colour photograph (taken 30 November 1988, on Ektachrome slide film) of a ZX Spectrum board with its Ferranti ULA visible among the other chips: an authentic period snapshot, not a modern museum photo.
    pedrik / Wikimedia Commons / CC BY 2.0. CC BY 2.0. Source
  • A Sinclair ZX Spectrum Issue 1 motherboard, full board, component side, bare (out of its case): the ULA, Z80A, ROM and RAM chips laid out, with the hand-soldered modification wires ('dead cockroach' fix) visible among the chips. High-resolution overhead photo.
    AUIC Oficial - (c) Fernando Sáenz - Public Domain Work / Wikimedia Commons / public domain. Source
  • A Sinclair ZX Spectrum Issue 4B motherboard, full board, component side, bare: a later production revision than Issue 1, chips and trace layout visibly different from the first boards.
    AUIC Oficial - (c) Fernando Sáenz - Public Domain Work / Wikimedia Commons / public domain. Source
  • A ZX Spectrum 48K motherboard, full board overview, component side, showing the overall chip layout (ULA, CPU, ROM, RAM banks) end to end.
    Bill Bertram / Wikimedia Commons / CC BY-SA 3.0. CC BY-SA 3.0. Source
  • The Sinclair ZX Spectrum+ (48K) main board, Issue 6A (1984), full board, component side: another board revision in the chip's production run.
    The original uploader was Powerhp at Italian Wikipedia . / Wikimedia Commons / CC BY-SA 2.5. CC BY-SA 2.5. Source
  • A Sinclair ZX Spectrum +2B (Amstrad-era) Issue 1 motherboard, part number Z70833, full board, component side: the later Amstrad-produced Spectrum variant's board layout.
    AUIC Oficial - (c) Fernando Sáenz - Public Domain Work / Wikimedia Commons / public domain. Source
  • A Sinclair ZX Spectrum (16K/48K rubber-key model), straight-on photograph of the complete keyboard and case, every key and its coloured BASIC-keyword labels legible.
    Nico Kaiser from München, Germany / Wikimedia Commons / CC BY 2.0. CC BY 2.0. Source
  • A labelled diagram over a photograph of the ZX Spectrum 48K's keyboard membrane, tracing the matrix wiring in red and white to show how the 8 half-rows of keys are wired for the ULA's port 0xFE to scan.
    Alejandro Sánchez / Wikimedia Commons / CC BY-SA 4.0. CC BY-SA 4.0. Source
  • A ZX Spectrum 48K's rubber-keyboard membrane removed from its case, showing the printed conductive traces under the keys.
    Alejandro Sánchez / Wikimedia Commons / CC BY-SA 4.0. CC BY-SA 4.0. Source
  • A black-and-white press photograph, 3 August 1984 (Nationaal Archief / Anefo, photographer Rob Bogaerts): two young women at a library demonstration, one operating a ZX Spectrum connected to a monitor, the other watching, a library lending a home micro-computer as an experiment.
    Nationaal Archief / Anefo, Rob Bogaerts. CC0. Source
  • A present-day museum display (MNACTEC, Terrassa, 'L'Enigma de l'Ordinador' exhibition) showing a ZX Spectrum (1982) connected to a contemporary round-screen television set, staged to resemble a period living-room setup.
    Enric / Wikimedia Commons / CC BY-SA 4.0. CC BY-SA 4.0. Source
  • Close-up macro photograph of two TMS4532 DRAM chips on a ZX Spectrum 48K board, the memory the ULA shares with the Z80, with surrounding resistors and traces sharply in focus.
    Alejandro Sánchez / Wikimedia Commons / CC BY-SA 4.0. CC BY-SA 4.0. Source
  • The retail box for a Sinclair ZX Spectrum 'Personal Computer', 48K RAM, shown at an angle: the black box with the Spectrum's rainbow stripe branding and a '48K RAM' sticker.
    Nico Kaiser from München, Germany / Wikimedia Commons / CC BY 2.0. CC BY 2.0. Source
  • Close-up macro photograph of the ZX Spectrum's 16K mask ROM, marked 'NEC D23128C', on a Spectrum 48K board.
    Bill Bertram / Wikimedia Commons / CC BY-SA 3.0. CC BY-SA 3.0. Source
  • A Sinclair ZX Spectrum connected by cable to a cassette recorder/monitor setup, wires visible running from its edge connector and power socket, photographed on a desk.
    JIP / Wikimedia Commons / CC BY-SA 4.0. CC BY-SA 4.0. Source
  • Close-up macro photograph of the ZX Spectrum's Z80A CPU, an NEC-made second-source part marked 'NEC D780C-1', on a Spectrum 48K board, solder joints and surrounding traces in focus.
    Bill Bertram / Wikimedia Commons / CC BY-SA 3.0. CC BY-SA 3.0. Source
  • The ZX Spectrum's Ferranti-made ULA, a 40-pin DIP chip marked 'FERRANTI ULA 6C001E-7 8543' (the Ferranti winged logo above the part number), photographed against a plain cyan background. The Spectrum's own chipset, part 6C001E-7, date code reads week 43 of 1985.
    Karlovarak / Wikimedia Commons / CC BY-SA 4.0. CC BY-SA 4.0. Source
  • The same ZX Spectrum ULA part, 6C001E-7, from a second-source die marked only 'ULA6C001E7' without a manufacturer logo (the Plessey-made example, per the file's own title), same chipset shot series as the Ferranti-branded chip, on a plain cyan background.
    Karlovarak / Wikimedia Commons / CC BY-SA 4.0. CC BY-SA 4.0. Source
  • The bare silicon die of the Acorn Electron's ULA, a Ferranti gate array of the same family and era as the Spectrum's, decapped and photographed in macro showing a dense grid of logic cells. A second, contemporary British Ferranti ULA for comparison.
    Revaldinho / Wikimedia Commons / CC BY 4.0. CC BY 4.0. Source
  • The bare die of a Ferranti ULA1U034JBS gate array, decapped and photographed in macro; the image shows distinct coloured regions (metal layers) over a grid of uncommitted logic cells, bond wires round the edge. A further example of Ferranti ULA die construction, same family as the Spectrum's chip.
    Revaldinho / Wikimedia Commons / CC BY 4.0. CC BY 4.0. Source
  • The bare silicon die of a Plessey Semiconductor (originally Ferranti) ULA 2C200J, decapped and photographed in extreme macro: a square grid of gate-array logic cells around the edge, bond wires visible as dark hooks around the perimeter. Not the Spectrum's own part number, but the same Ferranti ULA family and package (DIP28), made after Plessey took over Ferranti's semiconductor business in 1987 (date code 8832, 1988). Shows what the inside of a Spectrum-era Ferranti ULA looked like under the lid.
    Revaldinho / Wikimedia Commons / CC BY 4.0. CC BY 4.0. Source
  • The Sinclair ZX80's own circuit board ('platine'), showing its much simpler chip count than the Spectrum's board, the ZX80 has no ULA; the Z80 itself generates the display in software.
    Joho345 / Wikimedia Commons / CC BY-SA 4.0. CC BY-SA 4.0. Source
  • A boxed Sinclair ZX80, the complete unit photographed on a plain background, calculator-style keyboard and silver side trim visible.
    de:Benutzer:Stahlkocher / Wikimedia Commons / CC BY-SA 3.0. CC BY-SA 3.0. Source
  • A Sinclair ZX80 (1980), professionally photographed at the Computer History Museum: the complete machine, silver trim, calculator-style keyboard, on a plain background.
    Michael Hicks from Saint Paul, MN, USA / Wikimedia Commons / CC BY 2.0. CC BY 2.0. Source
  • A Sinclair ZX81 printed circuit board, Revision 3, component side, full board, chips and traces in sharp focus, high resolution.
    Binarysequence / Wikimedia Commons / CC BY-SA 4.0. CC BY-SA 4.0. Source
  • A hobbyist's home-built ZX80-style computer (stripboard circuit with a home-made keyboard, on a modern monitor) running a BASIC prime-number program: the picture drops to the monitor's 'NO SIGNAL' while it calculates, as the ZX80 did. Not an original Sinclair machine The calculation is shown sped up, with a burned-in 'Speed x10' caption.
    Fair-use candidate (copyright uploader, own hardware demonstration). Source
  • An unboxed Sinclair ZX81 'Personal Computer' retail kit laid out on blue cloth: the box, the computer itself, the membrane keyboard overlay, cables and small parts bags.
    Smaddison / Wikimedia Commons / CC BY-SA 3.0. CC BY-SA 3.0. Source
  • Close-up photograph of the ZX81's own Ferranti ULA chip, a 40-pin DIP, date code partly legible ('8128'), the predecessor chip to the Spectrum's ULA.
    Russian Rocket / Wikimedia Commons / CC BY-SA 3.0. CC BY-SA 3.0. Source

Music (10)

  • "Bit Quest" Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 4.0 License. CC BY 4.0. Source
  • "Chipper Doodle v2" Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 4.0 License. CC BY 4.0. Source
  • "Digital Lemonade" Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 4.0 License. CC BY 4.0. Source
  • "Equatorial Complex" Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 4.0 License. CC BY 4.0. Source
  • "Inspired" Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 4.0 License. CC BY 4.0. Source
  • "Investigations" Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 4.0 License. CC BY 4.0. Source
  • "Pixelland" Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 4.0 License. CC BY 4.0. Source
  • "Sneaky Snitch" Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 4.0 License. CC BY 4.0. Source
  • "Spy Glass" Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 4.0 License. CC BY 4.0. Source
  • "Voxel Revolution" Kevin MacLeod (incompetech.com), licensed under Creative Commons: By Attribution 4.0 License. CC BY 4.0. Source

Sources (51)