Superchip

Also called Super I/O, a Superchip is a hardware integrated circuit that integrates most of the "legacy" and low speed input and output (I/O) functions you would normally associate with a classic AT bus PC compatible system, however most modern Superchips are usually connected to the Southbridge or SoC using the LPC Bus as the ISA bus is no longer available on modern Southbridges.

Many modern Intel based boards do not have a Superchip at all or do not use the legacy I/O portions of the chip, using it only for temperature sensing and fan control, etc. Modern AMD Southbridges actually contain most of the functionality of the Superchip already making the chip mostly superflus, however many motherboard manufacturers still use Superchips as there is no price difference in quantity between them and simpler utility chips that provide only temperature sensing and control, and in addition to that many of the superchips are pin-compatible with each other, easing inventory concerns for manufacturers.

A typical Superchip will contain the following components:

Legacy ISA I/O and timers for IBM PC/AT & BIOS compatibility

A floppy drive controller
Parallel port (Printer port)
Two or more Intel 16C550 compatible RS-232 serial ports
An Intel 8254 compatible programmable interval timer.
A battery-backed real-time clock and tiny associated non-volatile BIOS memory.
A serial BIOS ROM interface

PS/2 I/O

PS/2 Bus controller (keyboard and mouse)

Environmental sensors and control

Temperature, voltage, and fan speed sensors alongside pulse-width modulation fan speed control.
Chassis intrusion detection

Sundry

Legacy Plug and Play support (for built-in devices only)
General purpose low speed I/O pins suitable for interfacing with Trusted Computing modules or environmental sensors for instance.

Optionally

An infrared port controller (Usually hooked up to the second on-board RS-232 port)
A game/a MIDI port
A watchdog timer
A consumer IR receiver (Suitable for remote controllers)

Historically Superchips also had a built-in dual IDE interface, but that is getting very rare, although some models are available for use in embedded computers.