ISA (pronounced eye-suh), which is an acronym for Industry Standard Architecture, is a data transfer standard introduced in the IBM PC in 1982.  An ISA bus,16-bit slot, is the oldest of the bus types, or data pathways.  It operates at 8 MHz clock rate and has a maximum data rate of 8 MBps.  It is typically still found in nearly every computer sold today, however the ISA buses are used only for slower devices like modems and most sound cards.

VESA Local Bus. A 32-bit slot, this originated in and was designed for 486 systems. Generally used by video cards and hard drive controllers. Cards in these slots are not plug-n-play. You won't see this in newer systems since it was replaced by AGP.

PCI, which stand for Peripheral Component Interconnect, was introduced in 1992. it is a 32-bit slot, mainly found in Pentium Class systems, but may also be found on some 486 systems.It operates at clock speeds of 33 or 66 MHz. At 32 bits and 33 MHz, a PCI bus has a maximum data rate of 132 MBps.

Sockets, or slots, for PCI cards are shorter than those for ISA plug-in cards.  The PCI Slot is generally used by IDE/SCSI controllers, video cards, network cards, video capture boards, and some sound cards.  Additionally some companies are starting to produce system upgrades (CPU, memory, etc...) using this bus.

Accelerated Graphics Port. This newest bus was designed to be used exclusively by the display adapter. The performance of AGP is increasing and the importance of this bus is quite obvious.