Southbridge is a chipset that manages the basic forms of input/output (I/O) such as Universal Serial Bus (USB), serial, audio, Integrated Drive Electronics (IDE), and Industry Standard Architecture (ISA) I/O in a computer. Southbridge is one of two chipsets that are collectively called Northbridge/Southbridge. Northbridge controls the processor, memory, Peripheral Component Interconnect (PCI) bus, Level 2 cache, and all Accelerated Graphics Port (AGP) activities. Unlike Northbridge, Southbridge consists of one chip, which sits on Northbridge's PCI bus.