A PCI mezzanine card or PMC is a printed circuit board manufactured to the IEEE P1386.1 standard. This standard combines the electrical characteristics of the PCI bus with the mechanical dimensions of the Common Mezzanine Card or CMC format (IEEE 1386 standard).
A PMC card can have 2 bus connectors ("P1" and "P2"), supporting 32 bit PCI signals; 3 bus connectors ("P1", "P2" and "P3") supporting 64 bit PCI signals, and / or a 4th bus connector ("P4") supporting non-specified I/O signals. In addition, arbitrary connectors can be supplied on the front panel, or "bezel".
The PMC standard defines which connector pins are used for which PCI signals; in addition it defines 64 of the (optional "P4") connector pins for use of arbitrary I/O signals.
It enables manufacturers to offer products that are compatible with the well-established PCI bus, but in a smaller and more robust package than standard PCI plug-in cards. The word mezzanine, meaning a platform inserted between two floors of a building, describes the way in which a PMC card fits between two adjacent host cards in a standard card rack, attached to one of the cards by connectors and mounting pillars. A single PMC measures 74 mm x 149 mm. The standard also defines a double-sized card, but this is rarely used.
Carrier cards that accept PMCs are usually made in the Eurocard format, which includes single, double and triple-height VME cards and compact PCI (cPCI) cards.
For the PMC standard, various I/O cards are available such as Serial communication controllers, SCSI controllers, Graphics controllers and Firewire controllers.
Additional standards exist that define variants of the standard PMC. For example,
- PMC-X (PCI-X PMC) defined by the VITA 39 standard
- PPMC (processor PMC) defined by the VITA 32 standard
- CCPMC (conduction-cooled PMC) defined by the VITA 20 standard
- XMC (PMC with high-speed serial fabric interconnect) defined by the VITA 42 standard. XMC specifies a 5th connector ("P5") that supports PCI Express (VITA 42.3) or other high speed serial formats such as Serial RapidIO (VITA 42.2) and Parallel RapidIO (VITA 42.1).