Mezzanine is a term used to describe the stacking of computer component card s into a single card that then plugs into the computer bus or data path. The bus itself is sometimes referred to as a mezzanine bus. The term derives from the Italian word, mezzano , which means middle. The more common use of this term is in architecture, where it is a low-ceilinged story between two main stories in a building. In theaters, a mezzanine is a balcony projecting partly over the ground floor below it.
A mezzanine card is a smaller form of the more familiar Peripheral Component Interconnect ( PCI ) or Industry Standard Architecture ( ISA ) card. The original and still most popular mezzanine card is the Industry Pack (IP) card. An IP card provides a 16-bit data path. The IP card is 3.9 x 1.8 inches and has two 50-pin connectors that plug into an IP-to-PCI adapter card. The IP-to-PCI adapter card usually holds up to three IP cards. Another popular mezzanine card is the PCI Mezzanine (PMC) card. This card provides 32 or 64-bit data paths and uses 64-pin connectors. Both types of mezzanine cards are widely used with VME bus , which is an expansion bus technology that supports up to 21 cards on a single backplane . VME bus is widely used in industrial, telecommunication, and military applications.