What is PCI / PCI Express

When we install a functionality expansion board in our computer desktop, most of the time it follows the PCI standard for connection, or its evolution PCI Express. What exactly does this mean?

PCI is a standardized way of connecting computer peripherals directly to the motherboard

The type of PCI slot is similar to ISA slots in idea, although different in Format, since the cards are installed in a similar way, although they have different sizes and speeds.

In the PCI card we have a string of contacts, which are visually an extension of the board, with plated contacts, which are inserted into the slot found on the motherboard.

This slot is divided into two sections, one longer than the other. The slot is raised above the motherboard and is white in color to distinguish it from other types of slots.

The acronym PCI stands for Peripheral Component Interconnect (Interconnection of Peripheral Components)

The standard allows self-configuration of the cards, so that when the computer boots, recognizes the peripherals connected by this standard, although later it will also need to load some

drivers specific to operating system so that the software can work with them.

This allows the same computer to assign certain resources to the card, as an interrupt (IRQ), which will be used automatically by the system. This assignment is done through direct "negotiation" between the PCI board and the BIOS.

The first version of the PCI standard was published in 1992, although it still did not mark how the slot to connect the expansion board and connectors. The following year, and in version 2.0 of the standard, the connection was defined. In 1995 version 2.1 of the standard was launched.

Between these versions, differences of velocity that take it from the original 33.3 MHz, through 66, to 133.

PCI Express (also abbreviated as PCIe or PCI-E) is an evolution of the PCI standard introduced in 2004 that consists of serial PCI

Speed ​​is increased thanks to the use of communications full-duplex, as the size of the bus decreases. We have, in fact, five types of slots, depending on whether they have one, two, four, eight or sixteen communication lanes for data transfer between the PCIe board and the system motherboard computer scientist.

Backward compatibility ensures that a manufacturer can convert a design PCI to a new PCI Express board just by adapting the physical connectors, keeping the same functioning Of the device.

Transfer speeds increase compared to its predecessor, reaching 250 MB / s in version 1.x and connector x1 (4 GB / s for connector x16), 500 Version 2.x MB / s with the x1 connector (8 GB / s for the x16), and 1969 MB / s on the x1 connector for version 4.0 of the PCIe standard (31.51 GB / s on the connector x16).

This latest version provides bandwidth as fast as the fastest version of the AGP connectivity standard for graphics cards.

That is why PCI Express is called not only to replace the PCI standard, but also to the other standards of peripheral card connectivity directly to the motherboard, such as the same AGP for graphics cards, simplifying the building motherboard and user purchases.

Photos: Fotolia - Sergii Shcherbakov / Giusepperg

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