The CPC was a home micro manufactured by Amstrad in the 1980s and early '90s.
First came the CPC464, in 1984. It had a fairly chunky (at the time) 64K of RAM, and a built-in cassette deck. Later models would come with a 3-inch disk drive instead (the 664) and a massive 128K of memory (the 6128).
All the CPCs were based around a 4MHz Zilog Z80 CPU. The operating system and BASIC programming language were built-in, on ROM chips. System disks for the operating system CP/M were supplied with add-on 3" disk drives and with the disk-based machines. 464 and 664 owners got CP/M 2.2, while 6128 owners got CP/M 3.1. CP/M was a sort of grandfather to MS-DOS, though CP/M enthusiasts tend to keep quiet about it.
There were many add-on widgets produced for the CPCs during its lifetime, certainly too many to describe here. Some of the more popular add-ons included:
The CPC464 was nicknamed "Arnold" during its development, and the name stuck. Eventually it came to be applied to the whole CPC range.
The 664 was once nicknamed IDIOT (for "Insert Disk Instead Of Tape"), and the 6128 was "Big IDIOT" (it had more RAM). But these names never caught on, and no-one ever really uses them.
In 1990, Amstrad decided to redesign and re-release the CPCs as the 464+ and the 6128+. These machines were based on the original CPC range, but with enhanced graphics and sound capabilities, a more streamlined case and a slot on top for games on cartridges. The cartridge format flopped, and so did the new machines. The home computing market had moved on, and kids now wanted shiny new Amigas, not Amstrads.
The CPC is still supported by a band of die-hard enthusiasts, many of whom can be found posting to comp.sys.amstrad.8bit. Recent developments include a CPC hard drive, an ISA interface and a TCP/IP stack (with talk of web browsers being developed!)