General-purpose input/output
A general-purpose input/output (GPIO) is an uncommitted digital signal pin on an integrated circuit or electronic circuit board which may be used as an input or output, or both, and is controllable by software.
Network router with three GPIOs (Banana Pi R1)
GPIO interface for Hewlett-Packard Series 80 computers (HP 82940A)
Ethernet interface to 48 GPIOs (Sensoray 2410)
Color coded GPIOs (top) on an Asus Tinker Board
A microcontroller or microcontroller unit (MCU) is a small computer on a single integrated circuit. A microcontroller contains one or more CPUs along with memory and programmable input/output peripherals. Program memory in the form of NOR flash, OTP ROM or ferroelectric RAM is also often included on chip, as well as a small amount of RAM. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications consisting of various discrete chips.
The die from an Intel 8742, an 8-bit microcontroller that includes a CPU running at 12 MHz, 128 bytes of RAM, 2048 bytes of EPROM, and I/O in the same chip
Two ATmega microcontrollers
A PIC 18F8720 microcontroller in an 80-pin TQFP package
Die of a PIC12C508 8-bit, fully static, EEPROM/EPROM/ROM-based CMOS microcontroller manufactured by Microchip Technology using a 1200 nanometer process