PCI Slot

A PCI (Peripheral Component Interconnect) Slot is a computer bus.  It attaches various hardware to a computer, and to each other in a computer.  Connected hardware comes in two forms:

• Planar Devices – an integrated circuit attached directly to the motherboard
• Expansion Card – a card that connects to the motherboard through a socket

PCI Buses are the standard computer expansion buses.  They replaced older bus types including ISA and VESA Local Bus.  Faster PCI versions exist, including PCI-X and PCI Express.

PCI's specification covers a number of attributes:

• Physical Bus Size – including spacing between wires
• Electrical signal characteristics
• Timing
• Protocols

PCI-SIG ( PCI Special Interest Group) sells the specification paper.

Computers use a variety of PCI cards:

• Network Interface Cards (NIC) – connect the PC to the network
• Sound Cards – create sound, beyond the old computer beeps, by converting between analog signals and digital data
• Modems – modulates data between analog and digital, for transport over a telephone wire
• USB and Serial Ports – connect a variety of devices
• Disk Controllers – interface between the CPU and the hard drive
• Video Cards – Because of increased video requirements, computers use AGP or PCI Express instead of PCI for all but the most basic video cards and requirements, such as connecting to a second monitor.

Motherboard mounted peripherals and USB connected devices have taken a lot of the load from PCI slots on modern computers.

Intel developed PCI beginning in 1990, and quickly used it in servers instead of older MCA (Micro Channel Architecture) or EISA (Extended Industry Standard Architecture) buses.  PCs at the time used VESA (Video Electronics Standards Association) Local Bus in conjunction with ISA and EISA Buses.  PCI didn't penetrate the PC market until 1994, and it completely replaced VESA Local Bus by 1997.  EISA and ISA remained in use until 2001.

Intel and others, working through a special interest group called the PCI-SIG,  later revised PCI, adding increased performance to the new PCI-X format.  PCI-X supports PCI (backwards compatibility.)  In 2004, the PCI-SIG introduced PCI Express, and at the same time they renamed PCI to Conventional PCI.  Conventional PCI still exists, but it's rare.

Later, the PCI-SIG created mini PCI for laptops.  Mini PCI cards have special features for laptop use, as well as inherent features:

• Smaller size
• Lower power consumption
• Support direct memory access
• Have limited external access and thus some limits to functionality

Mini PCI devices include:

• Wi-Fi cards
• Fast Ethernet network cards
• Bluetooth
• Modems – laptops use special modems called Winmodems.  These save space because, instead of having their own hardware features, they use more host computer resources.
• Sound Cards
• Various hard drive controllers

Mini PCI equipment works with standard PCI cards, and standard PCI equipment works with Mini PCI  cards, but these require conversion devices.

Consumer products specify the number of PCI (or PCI Express) slots, but not the size of those slots.  Slots come in a variety of sizes:

• Full sized
• Half length
• Even smaller sizes

Manufacturers develop PCI cards smaller than half length for these smaller than half length card slots.

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