Types of PCI Connectors and Cards

The PCI (Peripheral Component Interconnect bus) is currently the most common system bus for PC systems. It has very high speeds and bandwidths compared to older bus types, such as ISA. It is not hot-swappable and not as compact as USB, FireWire, and PCMCIA. PCI specifications categorize devices by card form factor and by connectors.

PCI Card Form Factors

The PCI card form factor has become a standard for PCs and is usually the best choice for transfer speed, economy, and availability.

PCI card form factors (H x L: maximum dimensions):

• Standard PCI and PCI-X: 107 x 312mm (4.2" x 12.283"), with a standard backplate
• Low-Profile PCI MD1: 64.41 x 119.91mm (2.536" x 4.72"), with a low-profile or standard backplate
• Low-Profile PCI MD2: 64.41 x 119.91 to 167.64mm (2.536" x 4.72" to 6.6"), with a low-profile or standard backplate

Maximum PCI Card Dimensions (Includes Connectors)

The Low-Profile PCI card form factor (introduced with the PCI v2.3 specification) reduced the size of PCI cards to accomodate smaller PC chassis. Low-Profile PCI cards are similar to standard PCI cards except that they are smaller and use a shorter mounting backplate. There are two standard card lengths: MD1, which can be up to 4.72" long, and MD2, which can be up to 6.6" long. Low-Profile backplates are 80mm high.

Although Low-Profile and standard PCI specifications define slightly different card and mounting backplate form factors, they both follow the same PCI specifications for the types of PCI bus connectors that the card is compatible with.

Type of PCI Connectors

The original 32-bit, 5V PCI standard began as an improvement over the then-common ISA bus. Over time, a 64-bit, 3.3V version was developed. Several intermediary standards have been introduced as enhancements to 32-bit, 5V PCI, using lower voltages and offering faster throughput.

Ideally slots and card connections would be keyed as 5V or as 3.3V only to prevent matching PCI components with dissimilar signal voltages. In reality, "Universal PCI" connectors were developed to ease the transition from 5V to 3.3V, while allowing for backwards compatibility with a customer's existing hardware.

PCI connector types:

• 32-bit 5V: Connectors with the notch farthest from the backplate
• 32-bit 3.3V: Connectors with the notch closest to the backplate
• 32-bit Universal PCI: Connectors with notches in both the 5V and 3.3V positions
• 64-bit 5V: 32-bit 5V PCI connectors with additional pins
• 64-bit 3.3V: 32-bit 3.3V PCI connectors with additional pins
• 64-bit Universal PCI: 32-bit Universal PCI connectors with additional pins

32-bit and 64-bit cards work together. 5V connectors (cards or slots) fit with 5V or with Universal PCI connectors. 3.3V connectors fit with 3.3V or with Universal PCI connectors. Universal PCI connectors fit with 5V, 3.3V, or Universal connectors.

When installing expansion cards into PC slots, care must be taken to confirm that the signal voltage is supported, as some manufacturers have produced cards that physically fit together, but do not have compatible signal voltages. Installing a 3.3V card into a 5V system, for example, could damage the card. Contact our Application Engineers for questions about our products.

PCI-X

PCI-X (PCI Extended) was designed as a high-performance improvement to the standard PCI specification. PCI-X v1.0 specifications increased the maximum clock frequency to 133MHz, while PCI-X v2.0 improved it to 533MHz. The PCI-X specification is fully backward-compatible with 3.3V PCI, using the same connector specifications and card form factors, supporting the same cards.

PCI and PCI-X