CPC-series Technical Details and Trivia


  • an expansion port for disk drives - 50-pin male edge connector. On Schneider models, this was replaced by a standard Centronics port.
  • a printer port (7-bit) - 34-pin male edge connector.
  • a single joystick/paddle port, incompatible with other systems, but joysticks come with a second port to allow daisy-chaining - 9-pin DB9 plug.
  • a monitor output socket (also used for TV modulators MP1 or MP2) - 6-pin round DIN.
  • a stereo headphone jack - 3.5mm - not present on some early CPC464s
  • a power supply socket (from either the monitor or the TV modulator) - 5V DC.

Technical Facts

  • The 3" Hitachi floppy drives are 40-track and the disks store 180K (178K in AMSDOS format) per side, or 360K in total. The drive interface is standard "Shugart", allowing Amstrad CPCs to use 3", 3.5", or 5.25" floppy drives as their second drive if required.
  • The CPC464 monitor (either green screen model GT64 or colour model CTM640) contains the computer's power supply. If the computer is to be used with a television, a seperate TV modulator (MP-1 for the CPC464 or MP-2 for the CPC664/6128) must be used which also contains a power supply for the computer. The monitors were different for the CPC664 and CPC6128 than the CPC464 because they included a 12V power supply for the floppy disc drive (and other accessories including the CT-1 Clock Timer) as well as the 5V power supply for the computer. The CPC664 monitor models were the green screen GT65 and the colour CTM644. Later CPC464s were sold with these monitors after Amstrad had sold out of their GT64 and CTM640 stock. For this reason the 12V power outlet from these later monitors was a socket to support a cable from the computer. All other connectors were hard-wired from the back of the monitor.
  • The CPC664 had the same output sockets and ports on the rear with the exception that the 664 and 6128 came with an additional 12V input needed to power the built-in floppy disk drive.
  • A rare accessory for owners of the CTM-644 monitor (supplied with the CPC6128) was the CT-1 Clock Timer. This was a clock radio that was designed to fit underneath the monitor, much like hi-fi separates units of the era that stacked on top of each other. The CT-1 was powered via the 12V output on the front of the monitor, and provided an LCD clock, alarm, and 3-band FM/MW/LW radio.
  • Another accessory for use with the CTM-644 monitor was the MP-3 TV tuner module. Like the CT-1 this would sit underneath the monitor itself as a 'separates' unit. It was used for viewing analogue TV channels on the CTM644 monitor. One downside to the design of the MP-3 is that there is no switch to easily select TV mode or computer mode - you had to manually unplug the 12V and RGB cables to switch from TV to CPC.


Hover your mouse over the circuit board for a description of the components

Component details reproduced with friendly permission from Sothius' Home, www.sothius.com


  • During development, the choice of using the Zilog Z80 CPU instead of the 6502 was interesting. Project "Arnold" was well behind schedule, and Locomotive Software who had been commissioned to write the BASIC interpreter for the new system (the CPC464) reckoned it would take 8 months to write BASIC for the 6502, but much less time if it were to use a Z80. Given that so little hardware had been completed to date it was decided that MEJ (the hardware firm) would start from scratch on building a Z80-based system.
  • The CPC464 was originally planned to be based on the 6502 microprocessor, but was changed around the time of the first Arnold prototype because at that time Locomotive BASIC was available only on the Z80 so the decision was made to use the Zilog Z80 microprocessor instead
  • The CPC464 could run CP/M , like the Commodore 128. But at the time, Microsoft's MS-DOS was beginning to take the lead over CP/M as the 'business' operating-system of choice. Amstrad even produced their own variant of CP/M 3.0, called CP/M Plus for the CPC6128 machine.
  • The CPC464 was pitched to compete directly with the Commodore 64. It supported more colours on-screen simultaneously, but the C64 supported hardware sprites and had better sound capability thanks to the SID chip, which meant the C64 was considered the better option for gaming.
  • Early CPC464s had what looked like the 3.5mm jack for headphones, but this was actually for an external cassette recorder. Later models used a 5-pin DIN connector for the same task.
  • The CPC464 had superior graphics and sound capabilities than the ZX Spectrum, but a lot of its games were ported directly from the Spectrum version due to them both making use of the Z80 microprocessor. This resulted in what was perceived by owners to be 'low quality' titles, although CPC-equivalent games didn't suffer the dreaded "colour clash" of the Spectrum version..
  • A special version of CPC464 was made for Spain. It was called the CPC472, and it did indeed have 72K RAM. This was to circumvent the additional Spanish tax for personal computers with 64K or lower RAM and that didn't have a Spanish keyboard. It was manufactured by Indescomp, Amstrad's Spanish distributor. The additional 8K of RAM was never connected to the board !
  • The CPC664's disks were double-sided, storing 169K on each side, but the drive only read one side at a time so you had to flip the disk to read the other side.
  • The CPC464's physical size was big, apparently because Alan Sugar dictated that it that way so it "looked like value for money"!
  • The decision to go with 3" floppy drives on the CPC664 and CPC6128 instead of the 3.5" size that was rapidly becoming the industry standard is sometimes wrongly claimed that Amstrad got hold a bulk load cheaply. This is not the case - Amstrad commissioned Panasonic to develop the drives specially. Other computer systems that made use of the 3" disk format were the Sega SF-7000, Tatung Einstein, and Osborne machines.
  • The CTM640, CTM644 and CM14 colour monitors can also be used to output RGB video from other computers, including the BBC Model B and Master, Spectrum +2A and +3, Sinclair QL, Commodore Amiga and ST. Do note however, that the pins will usually need to be reassigned for this to work.



This page was last updated on 6th April 2015.