Peripheral Component Interconnect

PCI is a motherboard slot type created by Intel for installing peripheral boards on the PCI. Nowadays is the most popular slot type.

Standard PCI slot works at 33 MHz transferring 32 bits per clock cycle, thus obtaining a maximum theoretical transfer rate of 132 MB/s (33 MHz x 32 bits / 8).

Other PCI standards with higher performance were created but with low market acceptance: 33 MHz x 64 bits (264 MB/s), 66 MHz x 32 bits (264 MB/s) and 66 MHz x 64 bits (528 MB/s).

Server motherboards usually have, besides PCI slots, PCI-X slots, which are high-performance PCI slots using bigger connectors, however.

A new kind of PCI slot was recently launched, called PCI Express. PCI Express works with serial communication (standard PCI slots work with parallel communication) and its basic transfer rate is of 250 MB/s for “1x” slots. “4x” slots work at 2,000 MB/s and “16x” slots work at 4,000 MB/s. Each speed grade (1x, 4x, 16x) uses a different connector type, see Figure 1. The most common PCI Express slots are 16x, used by video cards, and 1x, used by other PCI Express cards.

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Figure 1: PCI slots on a motherboard.