A PIC (Programmable Interface Controller) is an unbelievably cheap programmable device containing a CPU, some Flash memory (for your program code) and a limited amount of RAM. Low end ('12F') devices can be found on eBay for less than 20p each, contain an 8bit CPU, up to a kb of program space (Flash memory), a few dozen bytes of RAM and 4 to 6 i/o pins (the function of which is under your program control). All have built in timer/counter(s) and most have serial comms (I2C, SPI) circuits and some support 'Interrupts'. Some even have a built-in A-D converter and a dozen or so bytes of EEPROM ! They typically run at 1 MIPS.
Even the 'high end' PICs typically cost less than £5 each, for which you get a 16bit CPU running at 16MIPS (or so), multi-kb's of Flash instruction space (up to about 192kb), a few kb of RAM register space (up to about 8kb) and even some user EEPROM. Designed to run C program code they come with multiple 'built in' support components (such as a 10bit ADC, I2C, UART and even USB !)
