Sinclair ZX Spectrum +3

The ZX Spectrum +3, released in 1987, looked similar to the +2 but featured a built-in 3-inch floppy disk drive instead of the tape drive, and was in a black case. It was launched in 1987, initially retailed for £249 and then later £199 and was the only Spectrum capable of running the CP/M operating system without additional hardware.

The +3 saw the addition of two more 16 KB ROMs. One was home to the second part of the reorganised 128 ROM and the other hosted the +3’s disk operating system. This was a modified version of Amstrad’s PCWDOS (the disk access code used in LocoScript), called +3DOS. These two new 16 KB ROMs and the original two 16 KB ROMs were now physically implemented together as two 32 KB chips. To be able to run CP/M, which requires RAM at the bottom of the address space, the bank-switching was further improved, allowing the ROM to be paged out for another 16 KB of RAM.

The machine was a fairly big redesign over the +2, with new ports added, or changed. Probably the biggest difference was to the rear of the machine, which now sported an all new interface port for a printer and also for the allowance of a second disk drive.
Gone was the keypad port, it was replaced by an auxiliary port, which was used by such things as the Cheetah light gun.
The RS232 socket was retained, and because the machine now required more power, a larger PSU, and a DIN socket on the machine were needed, this larger plug did prevent some peripherals from being attached. In addition to the handling the music and FX out of the machine, the sound socket now also allowed a cassette deck to connect, to load games from tape. The RF socket remained unchanged.
The left side of the machine also remained the same and contained the two Sinclair joystick ports and the reset button.
The disk drive uses 3.0 disks, not the industry standard 3.5, these disks and drive loaded quickly, and were reasonably reliable.
Unlike previous models, the ZX Spectrum +3 power supply uses a DIN connector and has “Sinclair +3” written on the case. The same power supply could also be used with the later +2A/B models.

Almost all +3 machines have a sound fault, due to a component being left off the board, which means the sound is distorted and clips. The only models not to have the problem contain the 270835 motherboard, and only seem to appear in Spain.

The Spectrum +3 is considered the ultimate Spectrum model, gathering all the good points of the previous spectrum machines : 128k, convenient full-stroke keyboard, 3’’ built-in disk drive, 128k Basic, RAM disk, many interfaces. Unfortunately for Amstrad, the machine’s high cost, and games costing on average five pounds more on disk, sales of the computer and software were low, those who did buy the machine were happy enough to load cassette games in through the sound socket.
It was the last official Sinclair Spectrum model ever made. The +2A and +2B models vere launched a little later, but were just a revision of the +2 model already marketed. Production of the +3 ceased in December 1990, believed to be in response to Amstrad relaunching their CPC range. At the time, it was estimated about 15% of ZX Spectrums sold had been +3 models.

  • MANUFACTURER: Sinclair
  • TYPE: Home Computer
  • ORIGIN: United Kingdom
  • YEAR: 1987
  • BUILT IN LANGUAGE: 48K Spectrum BASIC (compatibility mode) and 128K Spectrum ZX+3 BASIC, integrated with +3 DOS
  • CPU: Zilog Z80 A
  • SPEED: 3.5469 MHz
  • RAM: 128 kb (8 x 16k pages)
  • ROM: 64 kb (4 x 16k pages)
  • TEXT MODES: 32 x 24
  • GRAPHIC MODES: 256 x 192
  • COLORS: 8 with two tones each (normal and bright)
  • SOUND: 3 channels, 8 octaves (Yamaha AY-3-8912)
  • SIZE / WEIGHT: 440 x 174 x 50 mm / 1,65 kg
  • I/O PORTS: UHF PAL TV port, Serial interface (RS232) port, Parallel Printer port (8 bit), Auxiliary interface port, RGB Monitor (and PERITEL TV) port, MIDI output port, Two Joystick ports, Audio Out/Cassette port, Second Disk Drive port, Expansion I/O port (full Z80 bus)
  • BUILT IN MEDIA: 3” Hitachi Floppy Disk Drive, single sided (40 track, 9 sector, 512 bytes/sector), CP/M compatible structure
  • Volatile RAM Drive
  • OS: +3DOS
  • POWER SUPPLY: External PSU (5V @ 2A, +12V @ 700mA, -12V @ 50mA) Same as Spectrum +2A/B PSU