Expansion Slots << Previous Next >> Summary

PCI PCI X Slots

An expansion slot is a receptacle on the motherboard for expansion cards. The first expansion slot we will discuss is the oldest covered by the CompTIA A+ hardware exam: the peripheral component interconnect (PCI). PCI was originally developed in the early 1990s to provide an expansion slot for network, video, audio, I/O (input/output), modem, and storage host adapter cards. It replaced older technology, such as the industry standard architecture (ISA) card, as a faster and more robust expansion card slot. It was found as a 32-bit interface supporting a maximum bus speed of 33 MHz. Later, it also offered a 64-bit variety at a speed of 66 MHz, but even this was not fast enough for the growing demand of faster CPUs. Along came the upgrade, called PCI-X, which is a faster, 64-bit version running at a bus speed of 133 MHz. This PCI-X, which is found on modern computers that still have a PCI/PCI-X slot, is fully backward compatible with older PCI cards, but if you mix them with newer PCI-X cards, the motherboard defaults back to the slower PCI speeds. The latest version, PCI-X 2.0 supports speeds of up to 266 MHz to 533 MHz, but has been replaced by the PCIe (PCI express) card slot standards for better speed/performance.

PCI supports a 32- or 64-bit I/O bus providing compatibility with both 486 and Pentium machines. Here are some facts about this slot:

This bus is processor independent (the CPU and the PCI bus can process concurrently).
PCI is plug-and-play, meaning that newly installed devices can be detected and configured automatically.
PCI buses are most commonly used for devices such as sound cards, modems, network cards, and storage device controllers.
The PCI bus is usually 32 bits wide, although 64-bit versions have been used as well. Running at 33 MHz, it can transfer data at 133 MBps (or 266 MBps for 64-bit versions).

PCI is an I/O bus that supports both 32- and 64-bit data paths and has been a standard expansion bus since the Intel 80486 (1989) chipset through all versions of Pentium, Apple Computers, and AMD chipsets. While PCI is definitely a legacy architecture, being replaced by PCIe and Thunderbolt interfaces, it is still included on current mainboards and definitely found in service in most computer workstations.

Expansion Slots << Previous Next >> Summary