ZX Spectrum

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Platform - ZXS.png
ZX Spectrum
ZX Spectrum 48K.jpg
Released: 1982-04-21
Discontinued: 1992-??-??
Developer: Sinclair Research
Type: Hardware

The ZX Spectrum (nicknamed Speccy) is an 8-bit home computer developed by UK-based Sinclair Research and released on April 21, 1982. At the time of its debut, it was an impressive computer, but four months later, the Commodore 64 (to this day, its archrival) was released making the Spectrum look outdated. Nevertheless, the low cost of the ZX Spectrum led to massive sales and widespread use throughout the UK, Spain, and clones from the USSR and CIS countries (notably Russia and Ukraine).


Due to the popularity of the ZX Spectrum, and the loyalty of fans, tens of thousands of games were released for the platform. Software was originally loaded from cassette tapes, but later models feature a 3" disk drive.


Although various models were released over the years, each with upgrades to the hardware, most Spectrum software is compatible with the original Spectrum 48K model.

ZX Spectrum 16K/48K

ZX Spectrum 48K

Upon its first release, the ZX Spectrum could be bought with 16K of on-board RAM, or 48K. This model features a poorly-made rubber keyboard. Display goes to a television, and audio consists merely of a PC Speaker. It boots directly into Sinclair BASIC.

Several companies sold peripherals, most popularly Fuller Box, that plug into the edge connector and combine an Atari joystick port, an amplifier, an AY-3-891x sound chip, and another edge connector as a passthrough to plug another peripheral in.

ZX Spectrum+

ZX Spectrum+

This model, released in 1984, is essentially a ZX Spectrum 48K with a wider case and better keyboard (created for a different platform, the Sinclair QL). It still uses a PC Speaker for audio.

ZX Spectrum 128K

ZX Spectrum 128K

This model goes by a lot of names: "ZX Spectrum+" and "128K" on the keyboard, "128 K SPECTRUM" on the board, "ZX Spectrum 128" on the box and in the manual, and "toast rack" or "toastrack" as a recent nickname, possibly to differentiate them from later models. Several emulators go with "ZX Spectrum 128K".

The actual hardware model rose the RAM to 128 KB, added an RGB monitor port, a built-in AY-3-8912 sound chip, and an RS-232 serial port that can be used for MIDI. The clocks also changed as shown below.


First released with a Spanish-language ROM in September 1985, the 128K also improved the BASIC editor.


Delayed at home till January 1986, the 128K added a boot menu.

ZX Spectrum +2

On 1986-04-07, Sir Clive Sinclair sold his brand (not the actual company) and ZX Spectrum line to Amstrad.

Similar to the Amstrad CPC464, the +2 added a built-in cassette drive and two joystick ports.

ZX Spectrum +2A

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ZX Spectrum +3

Similar to the Amstrad CPC664, the +3 replaced the cassette drive by a 3" disk drive. A ZX Spectrum game and a CPC game can be stored on the same disk.

ZX Spectrum +2B/+3B

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Music and Sound

Every ZX Spectrum has several built-in components:

  • a Z80 CPU to program and run games and music drivers.
  • a PC Speaker (called loudspeaker on the board and in the manual) to write 1-bit PCM to. This takes a lot of CPU time, hence loudspeaker music rarely plays in-game.
  • a ROM with a BEEP command that programmers can call from both BASIC and Z80 machine code to easily play a square wave in 10 octaves.
  • an edge connector to plug peripherals in.
  • a screen refresh interrupt to run things at a steady rate, like animations and AY-3-891x music.

Sinclair's models have two 3.5 mm jacks called EAR and MIC. Both are used to access data on tape cassette and to amplify the loudspeaker. As detailed above, several peripherals and models have a built-in AY-3-891x sound chip. However, most boards put the same chip at a different address, rendering them incompatible after all. On the unintended model, pitch and speed are off by 23 cents. The clocks are:

Models CPU Screen refresh
48K 3500000 Hz 50.08 Hz
128K and later 3546900 Hz 50.021 Hz


When arranging for the loudspeaker, many programmers "misused" bits of the ROM as noisy sound effects and percussion. Some knew how to do pulse width modulation or mix multiple voices together. They were able to push the loudspeaker to the limit and play very impressive sounding tunes.

When arranging for the AY-3-8912, many programmers tuned their music driver at 438 Hz or even 390 Hz (two semitones lower), possibly as a simplified port from the Amstrad CPC.

Some games came with arrangements for both outputs. To determine which should be used, the game either shows a setup, detects the Spectrum 128K (not peripherals) in various ways, or came in separate versions. Simultaneous usage of different outputs was rare on the Spectrum, but still more common than on any other home computer.