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ZX Spectrum

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The Sinclair ZX Spectrum was a small home computer released in the United Kingdom in 1982 by Sinclair Research. Based on a Zilog Z80 CPU running at 3.50 MHz, the Spectrum came with either 16 KB or 48 KB of RAM. Users with 16KB Spectrums could upgrade them to 48k versions. The hardware designer was Richard Altwasser of Sinclair Research and the software was written by Steve Vickers on contract from Nine Tiles Ltd, the authors of Sinclair BASIC. Sinclair's industrial designer Rick Dickinson was responsible for the machine's outward appearance. Originally dubbed the ZX82, the machine was later renamed the "Spectrum" by Sinclair to highlight the machine's colour display, compared to the black-and-white of its predecessors, the ZX80 and ZX81.

The original 1982 ZX Spectrum.
The original 1982 ZX Spectrum.


Description

Video output was to a TV, for a simple colour graphic display. The rubber keyboard (on top of a membrane, similar to calculator keys) was marked with Sinclair BASIC keywords, so that, for example, pressing "G" when in programming mode would insert the BASIC command GO TO. Programs and data were stored using a normal cassette recorder.

ZX Spectrum rubber keyboard
ZX Spectrum rubber keyboard

The Spectrum's video display, although rudimentary by today's standards, was perfect at the time for display on portable TV sets, and didn't present much of a barrier to game development. Text could be displayed using 32 columns × 24 rows of characters from the Spectrum Character Set, with a choice of 8 colours in either normal or bright mode, which gave 15 shades (black was the same in both modes). The graphics resolution was 256×192 with the same colour limitations. The Spectrum had an interesting method of handling colour; the colour attributes were held in a 32×24 grid, separate from the text or graphical data, but was still limited to only two colours in any given character cell. This led to what was called colour clash or attribute clash with some bizarre effects in arcade style games. This problem became a distinctive feature of the Spectrum and an in-joke among Spectrum users, as well as a point of derision by advocates of other systems. Other machines available around the same time, for example the Commodore 64 and Amstrad CPC, did not suffer from this problem.

The Spectrum was the first mainstream audience home computer in the UK, similar in significance to the Commodore 64 in the USA. The Commodore 64, often abbreviated to C64, was also the main rival to the Spectrum in the UK market. An enhanced version of the Spectrum with better sound, graphics and other modifications was marketed in the USA by Timex as the TS2068.

Models

ZX Spectrum (1982)

Released by Sinclair in 1982 and available with either 16KB (£125, later £99) or 48KB (£175, later £129) of RAM and 16KB ROM, the original Spectrum is remembered for its rubber keyboard and diminutive size. Owners of the 16K model could purchase an external 32K RAMpack that mounted in the rear expansion slot. As with the ZX81, "RAMpack wobble" caused by poor connection with the expansion was the bane of many users, causing instant crashes and sometimes ULA or CPU burnout. Also available was an internal 32K RAM update, which consists of 8 dynamic RAMs and few TTL chips. Users with 16K Spectrums could mail them to Sinclair to be upgraded to 48K versions.

ZX Spectrum+ with third-party joystick interface installed.

ZX Spectrum+ (1984)

This 48K Spectrum had a much needed solid keyboard and reset button, retailing for £180. An upgrade package for older machines was also available. Most hard core users (programmers and gamers) disliked the new keyboard, but the new style helps the Spectrum to look less like a toy and more like a computer.

ZX Spectrum 128K (1986)

Sinclair developed the 128K in conjuction with their Spanish distributor Investrónica. Investrónica had helped adapt the Spectrum+ to the Spanish market after Spanish courts decreed all computers with 64 KB RAM or less must support the Spanish alphabet (including ñ) and show messages in Spanish.

New features included 128 KB RAM, three-channel audio via the AY-3-8912 chip, MIDI compatibility, an RS-232 serial port, an RGB monitor port, improved BASIC editor and an external keypad.

The machine was presented at SIMO '85 in Spain, with a price of 44.250 pesetas (266 €), where it was subsequently launched. A UK release followed without an external keypad available although the ROM routines to utilise it and the port itself remained, hastily renamed "AUX".

The Z80 processor used in the Spectrum has a 16-bit address bus which means only 64 KB of memory can be addressed. To facilitate the extra 96 KB of RAM the designers utilised a bank switching technique so that the new memory would be available as 6 pages of 16 KB at the top of the address space. The same technique was also used to page between the new 16 KB editor ROM and the original 16 KB BASIC ROM at the bottom of the address space.

The new sound chip and MIDI out abilities were exposed to the BASIC programming language with the command PLAY and a new command SPECTRUM was added to switch the machine into 48K mode. To enable BASIC programmers access to the additional memory a RAM disk was created where files could be stored on the additional 96 KB of RAM. The new commands took the place of two existing user-defined-character spaces causing compatibility issues with some BASIC programs.

ZX Spectrum +2 (1986)

Shortly after Amstrad's buyout of Sinclair Research in 1986 came the ZX Spectrum +2. It featured a new, grey casing, distinguishing itself from the familiar black of previous Spectrums. The case also integrated a new spring loaded keyboard, dual joystick ports, and a built-in cassette recorder dubbed the "Datacorder" (like the Amstrad CPC 464). The +2 was otherwise essentially the same as the 128 model. Production cost cutting saw the retail price drop to £139-£149.

ZX Spectrum +3 (1987)

File:SpectrumPlus3Menu.gif
Power-on menu on Spectrum +3.

The Spectrum +3 was an Amstrad produced version, based on the +2 but featuring a built-in 3-inch floppy disk drive (like the Amstrad CPC 6128). Most models featured distorted sound due to a design fault, which was later rectified in the "4.1 ROM" model. This machine retailed for £249, then later for £199, and was the only model capable of running CP/M without additional hardware.

The +3 saw the addition of two more 16K ROMs, now physically implemented as two 32K chips. One was home to the second part of the reorganised 128K ROM, the other hosted the +3's disk operating system.

Such core changes brought incompatibilities:

  • Removal of lines on the edge connector - Caused many external devices problems, some such as the VTX5000 modem could be used via a FixIt device
  • Reading a non-existent IO port no longer returned the last attribute - Caused some games such as Arkanoid to be unplayable
  • Memory timings - Some of the RAM banks were now contended causing high-speed colour-changing effects to fail
  • The keypad scanning routines from the ROM was removed. The physical port was renamed Auxiliary

Many older 48K, and some older 128K, games were incompatible with the machine.

The ZX Spectrum +3 was the final official model of the Spectrum to be manufactured, remaining in production until December 1990. Although still accounting for one third of all home computer sales at the time, production of the model was ceased by Amstrad in an attempt to transfer custom to their CPC range.

ZX Spectrum +2A /+2B (1987)

The +2A was produced to homogenize Amstrad's range. Although the case reads "ZX Spectrum +2", the +2A/B is easily distinguishable from the original +2 as the case was restored to the standard Spectrum black.

The +2A was derived from Amstrad's +3 4.1 ROM model, hosting a new motherboard which vastly reduced the chip count, integrating many of them into a new ASIC. The +2A replaced the +3's disk drive and associated hardware with a tape drive, as in the original +2. Originally, Amstrad planned to introduce an additional disk interface, but this never appeared. If an external disk drive was added, the "+2A" on the system OS menu would change to a +3. As with the ZX Spectrum +3 many older 48K, and some older 128K, games were incompatible with the machine.

The +2B signified a manufacturing move from Hong Kong to Taiwan.

Clones

Sinclair licensed the Spectrum design to Timex in the USA which produced their own, largely incompatible, derivatives. However, some of the Timex innovations were later adopted by Sinclair Research. A case in point was the abortive 'Pandora' portable Spectrum, whose ULA had the high resolution video mode pioneered in the TS2068. 'Pandora' had a flat-screen TV monitor and Microdrives and was intended to be Sinclair's business portable - after Alan Sugar bought the computer side of Sinclair, he took one look at it and ditched it. (A conversation between him and UK computer journalist Guy Kewney went thus: GK: "Are you going to do anything with Pandora?" AS: "Have you seen it?" GK: "Yes" AS: "Well then.")

In the UK, Spectrum peripheral vendor Miles Gordon Technology (MGT) released the SAM Coupé as the natural successor with some Spectrum compatibility. However, by this point, the Commodore Amiga and Atari ST had taken hold of the market, leaving MGT in eventual receivership.

Many unofficial Spectrum clones were produced, especially in Eastern Europe and South America. A non-exhaustive list at Planet Sinclair lists over 50 such clones. Some of them are still being produced such as the Sprinter.

Technical specifications

ZX Spectrum motherboard (Issue 3B - 1983)
  • CPU
    • Zilog Z80A CPU, 3.50 MHz (Spectrum 16K, 48K, +) or 3.5469 MHz (Spectrum 128K and later)
  • Read-only memory (ROM)
    • 16 KB ROM (BASIC: Spectrum 48K, +)
    • 32 KB ROM (BASIC, Editor: Spectrum 128K, +2)
    • 64 KB ROM (BASIC, Editor, Syntax check, DOS: Spectrum +3, +2A, +2B)
  • Random-access memory (RAM)
    • 16 KB RAM (Spectrum 16K)
    • 48 KB RAM (Spectrum 48K, +)
    • 128 KB RAM (Spectrum 128K, +2, +3, +2A, +2B)
  • Display
    • Text: 32×24 characters
    • Graphics: 256×192 pixels, 15 colours (two simultaneous colours - "attributes" - per 8×8 pixels, causing attribute clash)
  • Sound
    • Beeper (1 channel, 5 octaves: Spectrum 16K and 48K via internal speaker, others via TV)
    • AY-3-8912 chip (3 channels, 7 octaves: Spectrum 128K, +2, +2A, +3)
  • I/O
    • Z80 bus in/out
    • Tape audio in/out (all except Spectrum +2)
    • RF television out
    • RS-232 in/out (128K models)
    • MIDI out (128K models)
    • RGB monitor out (128K models)
    • Joystick inputs, 2 (Spectrum +2, +2A, +3)
    • External numeric keypad (Spectrum 128K and +2)
    • Auxiliary interface (previously keypad port) (Spectrum +2A, +3)
    • Parallel Printer port (Spectrum +2, +2A, +3)
    • Second disk drive port (Spectrum +3)
  • Storage

Peripherals

Several peripherals for the Spectrum were marketed by Sinclair: the printer was already on the market, as the Spectrum had retained the protocol for the ZX81's printer. The Interface 1 added a standard RS-232 serial port, a proprietary format local area networking port, and the ability to connect up to eight ZX Microdrives – somewhat unreliable but speedy tape-loop storage devices. These were later used in a revised version on the Sinclair QL, whose storage format was electrically compatible but logically incompatible with the Spectrum's. Sinclair also released the ZX Interface 2 which added two joystick ports and a ROM cartridge port.

There were also a plethora of third-party hardware addons. The better known of these included the Kempston joystick interface, the Currah Microspeech unit (speech synthesis), RAM pack, and SpecDrum (Drum machine), and the Multiface (snapshot and disassembly tool), from Romantic Robot. There were numerous disk drive interfaces, including the Opus Discovery and the DISCiPLE/PlusD from Miles Gordon Technology. During the mid-80s, the company Micronet800 launched a service allowing users to connect their ZX Spectrums to a network known as Micronet hosted by Prestel. This service had some similarities to the Internet, but was proprietary and fee-based.

Software

The Spectrum family enjoyed a very large software library of at least 20,000 titles. Despite the fact that the Spectrum hardware was limited by most standards, its software library was very diverse, including programming language implementations (C, Pascal, Prolog, Forth, several Z80 assemblers/disassemblers (eg: Devpac, ZEUS, Artic Assembler), Sinclair BASIC compilers (eg: MCoder, COLT), Sinclair BASIC extensions (eg: Beta Basic, Mega Basic), databases (eg: VU-File), word processors (eg: Tasword II), spread sheets (eg: VU-Calc), drawing and painting tools (eg: Art Studio, Artist, Paintbox, Melbourne Draw), and, of course, many, many games.

A number of current leading games developers and development companies began their careers on the ZX Spectrum, including Peter Molyneux (ex-Bullfrog Games), David Perry of Shiny Entertainment, and Ultimate Play The Game (now known as Rare, maker of many famous titles for Nintendo game consoles). Other prominent games developers include Matthew Smith (Manic Miner, Jet Set Willy), and Jon Ritman (Match Day, Head Over Heels).

Most Spectrum software was originally distributed on audio cassette tapes. The software was encoded on tape as a sequence of alternating pitches, similar to the sounds of a modern day modem, using Frequency-shift_keying. Standard speed was 1500 baud (in this case 1 baud = 1 bit per second) but higher speeds were possible using custom machine code loaders instead of the ROM routines. Complex loaders with unusual speeds or encoding were the basis of the ZX Spectrum copy prevention schemes, although other methods were used including asking for a particular word from the documentation included with the game - often a novella - or the notorious Lenslok system. This had a set of plastic prisms in a fold-out red plastic holder: the idea was that a scrambled word would appear on the screen, which could only be read by holding the prisms at a fixed distance from the screen courtesy of the plastic holder. This relied rather too much on everyone using the same size television, and Lenslok became a running joke with Spectrum users.

A standard 48 K program would take about 4.5 minutes to load: 49152 bytes * 8 = 393216 bits; 393216 bits / 1500 baud = 262.14 seconds = 4.36 minutes. Curiously, experienced users could tell the type of a file, e.g. machine code, BASIC program, or screen image, from the way it sounded on the tape.

One very interesting kind of software was copiers. Most were piracy oriented, and their function was only tape duplication, but when Sinclair Research launched the ZX Microdrive (later with a diskette system), copiers were developed to copy programs from audio tape to microdrive tapes or diskettes. Best known were the LERM copiers produced by Lerm Software, Omni Copy 2, and others. As the protections became more complex (e.g. Speedlock 1-8) it was almost impossible to use copiers to copy tapes, and the loaders had to be cracked by hand, and unprotected versions produced. This was, of course, illegal, but in the 1980s most of South and Eastern Europe didn't have software copyright laws.

The Spectrum was intended to work with almost any cassette tape player, and despite differences in audio reproduction fidelity, the software loading process was quite reliable; however all Spectrum users knew and dreaded the "R Tape loading error, 0:1" message.

Typical settings for loading were 3/4 volume, 100% treble, 0% bass. Audio filters like loudness and Dolby Noise Reduction had to be disabled, and it was not recommended to use a Hi-Fi player to load programs. There were some tape recorders built specially for digital use, such as the Timex Computer 2010 Tape Recorder.

In addition to tapes, software was also distributed through print media, fan magazines, or books. The prevalent language for distribution was the Spectrum's BASIC dialect Sinclair BASIC. The reader would type the software into the computer by hand, run it, and save it on tape for later use. The software distributed in this way was in general simpler and slower than its assembly language counterparts, and lacked graphics, but soon, magazines were printing long lists of checksumed hexadecimal digits with machine code games or tools. There was a vibrant scientific community built around such software, ranging from satellite dish alignment programs to school classroom scheduling programs.

One unusual software distribution method was a radio or television show, in Poland or Czechoslovakia for example, where the host would describe a program, instruct the audience to connect a cassette tape recorder to the radio or TV and then broadcast the program over the airwaves in audio format.

Other unusual method were 33⅓ rpm floppy or soft disks, not the hard vinyl ones, that were played on a standard hifi pickup of a record player. These disks were known as "floppy ROMs,". This method was used in France by some magazines. See: "Unusual types of gramophone record#Unusual materials".

A few pop musicians included Sinclair programs on their records. Ex-Buzzcock Peter Shelly put a Spectrum program including lyrics and other information as the last track on his XL-1 album. Festival favourites Hawkwind put a Spectrum database of band information on their 1984 release, 'New Anatomy'. Also in 1984, the Thompson Twins released a game on vinyl. The Freshies had a brief flirtation with fame and Spectrum games, and the Aphex Twin included various loading noises on his Richard D. James album in 1996 - most notably the loading screen from Sabre Wulf on Corn Mouth.

As audio tapes have a limited shelf-life, most Spectrum software has been digitized in recent years and is available for download in digital form. One popular program for digitizing Spectrum software is Taper: it allows connecting a cassette tape player to the line in port of a sound card or, through a simple home-built device, to the parallel port of a PC. Once in digital form, the software can be executed on one of many existing emulators, on virtually any platform available today. Today, the largest on-line archive of ZX Spectrum software is The World of Spectrum site with more than 12,000 titles.

The Spectrum enjoys a vibrant, dedicated fan-base. Since it was cheap and simple to learn to use and program, the Spectrum was the starting point for many programmers and technophiles who remember it with nostalgia. The hardware limitations of the Spectrum imposed a special level of creativity on game designers, and for this reason, many Spectrum games are very creative and playable even by today's standards.

Notable titles

Your Sinclair top 10

Between July and November 1991 Your Sinclair published a list of what they considered to be the top 100 games for the ZX Spectrum. Their top 10 were:

  1. 3D Deathchase
  2. Rebelstar
  3. All or Nothing
  4. Stop the Express
  5. Head Over Heels
  6. R-Type
  7. The Sentinel
  8. Rainbow Islands
  9. Boulder Dash
  10. Tornado Low Level

Crash top 10

Between August and December 1991 Crash published their list of the top 100 ZX Spectrum games, including in the top 10:

  1. Rainbow Islands
  2. Chase HQ
  3. Robocop
  4. Robocop 2
  5. Dizzy
  6. Target: Renegade
  7. Magicland Dizzy
  8. Batman - The Movie
  9. Operation Wolf
  10. Midnight Resistance

In Crash's Top 10 all but the Dizzy games were published by Ocean Software. It is also interesting to note that all but one of the Your Sinclair Top 10 games were released in 1987 or before (the conversion of Rainbow Islands did not appear until 1989, although the original was released in 1987), in comparison to the Crash Top 10 which exclusively features games released in 1987 or after. 1987 was the year in which use of the newer 128K architecture and of the newer AY-3-8912 sound chip began to take off. Indeed, all of Crash's Top 10, with the exception of Dizzy, made use of these new features with enhanced sound and preloaded levels (eliminating the need for a multiload), reflecting a difference in the attitudes of the editorship and readership of the two magazines.

See also: World of Spectrum top 100

Screenshots

Screenshot from "3 Weeks in Paradise" Screenshot from "Chuckie Egg" Screenshot from "Elite"
3 Weeks in Paradise Chuckie Egg Elite
Mikrogen (1985) A&F (1984) Firebird (1985)
Screenshot from "Jet Set Willy" Screenshot from "Knight Lore" Screenshot from "Saboteur"
Jet Set Willy Knight Lore Saboteur
Software Projects (1984) Ultimate (1984) Durell (1987)

Magazines

See also

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