The ZX Spectrum +3, released in 1987, looked similar to the +2 but featured a built-in 3-inch floppy disk drive (like the Amstrad CPC 6128) 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.

Such core changes brought incompatibilities:

  • Removal of several lines on the expansion bus edge connector (video, power, and IORQGE); caused many external devices problems; some such as the VTX5000 modem could be used via the “FixIt” device.
  • Dividing ROMCS into two lines, to disable both ROMs.
  • Reading a non-existent I/O port no longer returned the last attribute; caused certain games such as Arkanoid to be unplayable.
  • Memory timing changes; certain RAM banks were now contended causing high-speed colour-changing effects to fail.
  • The keypad scanning routines from the ROM were removed.
  • Some older 48K and 128K games were incompatible with the machine. The ZX Interface 1 was incompatible due to differences in ROM and expansion connector, making it impossible to connect and use the Microdrive units.

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.

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. Production of the +2B (the only other model then still in production) continued, as it was believed not to be in competition with other computers in Amstrad’s product range.

I did play a bit with the Spectrum +3, more because I had the lick of getting about twenty 3" floppy disks with games. However, due to their age, most of them don’t work anymore. However, a few do work fine and the games were pretty fun to play, making you see the big advances in video game design, control, usability and graphics.