page_title: ZX Spectrum
section_title: ZX Spectrum +3
hierarchical_section_title: ZX Spectrum / Amstrad models / ZX Spectrum +3
caption_attribution_description: ZX Spectrum +3
context_page_description: The ZX Spectrum is an 8-bit personal home computer released in the United Kingdom in 1982 by Sinclair Research.
  Referred to during development as the ZX81 Colour and ZX82, it was launched as the ZX Spectrum by Sinclair to highlight the machine's colour display, compared with the black and white display of its predecessor, the ZX81. The Spectrum was released as eight different models, ranging from the entry level with 16 KB RAM released in 1982 to the ZX Spectrum +3 with 128 KB RAM and built in floppy disk drive in 1987; together they sold over 5 million units worldwide.
  The Spectrum was among the first mainstream-audience home computers in the UK, similar in significance to the Commodore 64 in the US. The introduction of the ZX Spectrum led to a boom in companies producing software and hardware for the machine, the effects of which are still seen. Some credit it as the machine which launched the UK IT industry. Licensing deals and clones followed, and earned Clive Sinclair a knighthood for services to British industry.
  The Commodore 64, Dragon 32, Oric-1, Oric Atmos, BBC Micro and later the Amstrad CPC range were rivals to the Spectrum in the UK market during the early 1980s.
context_section_description: The ZX Spectrum +3, released in 1987, looked similar to the +2A 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.
  Move 1 byte address in ROM.
  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.
  There was a regression in sound quality from the previous 128K models – an error with a resistor placement meant sound was distorted.
  The ZX Spectrum +3 power supply provides the same voltages as the one supplied with +2A/B. This power supply has the same DIN connector so can be used with the +2A/B. The power supply purchased with the +3 had "Sinclair +3" written on the case.
  
  Production of the +3 ceased in December 1990, believed to be in response for 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.
caption: ZX Spectrum +3
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