Super I/O

Diagram of a motherboard, which supports many on-board peripheral functions as well as several expansion slots.

ITE Super I/O chip (IT8712F)

SMSC (now Microchip) Super I/O chip (FDC37M813) on IBM motherboard

Super I/O is a class of I/O controller integrated circuits that began to be used on personal computer motherboards in the late 1980s, originally as add-in cards, later embedded on the motherboards. A super I/O chip combines interfaces for a variety of low-bandwidth devices. The functions below are usually provided by the super I/O if they are on the motherboard:

• A floppy-disk controller^[1]
• An IEEE 1284-compatible parallel port^[1] (commonly used for printers)
• One or more 16C550-compatible serial port UARTs^[1]
• One or more embedded controllers including the keyboard controller
• PS/2 keyboard and/or mouse interface.

Most Super I/O chips include some additional low-speed devices, such as:

• Temperature, voltage, and fan speed sensors^[2][3]
• Chassis intrusion detection
• Pulse-width modulation fan speed control^[4]
• A serial BIOS ROM interface (if the ROM is not directly on the LPC bus itself)
• An infrared port controller
• A game port (not provided by modern super I/O chips anymore because Windows XP is the last Windows OS to support a game port)
• A watchdog timer
• A consumer IR receiver
• a MIDI port
• Some general-purpose input/output pins
• Legacy Plug and Play support for the included devices

By combining many functions in a single chip, the number of parts needed on a motherboard is reduced, thus reducing the cost of production.

The original super I/O chips communicated with the central processing unit via the Industry Standard Architecture (ISA) bus. With the evolution away from ISA towards use of the Peripheral Component Interconnect (PCI) bus, the Super I/O chip was often the biggest remaining reason for continuing inclusion of ISA on the motherboard.

Later super I/O chips use the Low Pin Count (LPC) bus instead of ISA for communication with the central processing unit. This normally occurs through an LPC interface on the southbridge chip of the motherboard.

Since Intel is replacing the LPC bus with the Enhanced Serial Peripheral Interface Bus (eSPI) bus, super I/O chips that connect to that bus have appeared on the market.

Companies that make super I/O controllers include Nuvoton (formerly Winbond),^[1]ITE Tech [zh],^[1][3] Fintek,^[5] and Microchip Technology. National Semiconductor used to make super I/O controllers but sold that business to Winbond at 2005, which already had a competing super I/O controller business. In 2008, Winbond then spun off its logic businesses to a wholly owned subsidiary, Nuvoton. SMSC made super I/O chips and then got acquired by Microchip Technology.