Board Form Factors
The size and shape of an electronic equipment chassis is dictated by a number of factors. The type of card used within the chassis plays a large role, but many of the Board configurations result in the same size case.
The component within the Electronic Enclosure that really holds the boards is the card cage. The card cage is a metal frame with card rails and attachment points so that it can be secured to the chassis and a backplane secured to it. The type and style of card format being used dictates the size of the card cage.
There are a number of competing board formats. Many of the board formats are only used in the industrial or embedded area. The common PC card formats are PCIe, PCI, and AGP standards. The common embedded card formats are VME, cPCI, ATCA, and PC-104, but there are many others. Refer to the BackPlane Buses page for a complete list of possible backplane card combinations.
Normally at the start of a design the board format is decided upon. Once the design matures the card functions need to partitioned and the number of cards within a chassis starts to be fixed. There is a finite number of cards that a chassis will hold, and a fixed number depending on the bus standard used.
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