PCI Card Size [3.3 Volt Keyed]

The standard PCI card form factor is 106.68mm x 312mm. The standard defines two sizes; a long form and short form factor board.
Both card formats are shown below, note the keep-out for the short-form card.
Also note the component keep-outs shown in yellow.
The difference between the 5 volt PCI card and the 3.3 volt card is the location of the key on the board [missing fingers on the card edge].
So the key changes position, but the board size remains the same between a 3.3V or 5V card.
The key location shown is for a 3.3 volt cards or Universal cards [56.21mm off the edge].
The key location for a 5 volt card is 104.47mm off the card edge.

PCI Bus CCA Card Size and Dimensions
Short PCI Card Dimensions / Long PCI Card Dimensions

Four sizes of PCI add-in cards are defined: long, short, Low Profile, and variable short length. Systems are not required to support all add-in card types. The long add-in cards include an extender to support the end of the add-in card. To accommodate the 3.3V and 5V signaling environments and to facilitate a smooth migration path between the voltages, two add-in card electrical types are specified: a "universal" add-in card which plugs into both 3.3V and 5V connectors and a "3.3 volt" add-in card which plugs into only the 3.3V connector.

The Peripheral Component Interface 'PCI' interface Bus was developed as a local bus expansion for the PC ISA bus. The PCI specification defines the Electrical and physical requirements for the board interface. No bus terminations are specified, the bus relies on signal reflection to achieve a valid voltage level threshold. The first version of the PCI bus ran at 33MHz with a 32 bit bus (133MBps), the current version runs at 66MHz with a 64 bit bus. The PCI bus operates either synchronously or asynchronously with the "mother Board" bus rate. While operating asynchronously the bus will operate at any frequency from 66MHz down to (and including) 0Hz. PCI is an unterminated bus, the signal rely on signal reflections to attain there final value.

The PCI connector pins define the PCI Bus Pinout. The card draws power from the Mother Board. Pin arrangements are defined for +5 volts, +3.3 volts, or +5 and +3.3 volts. The +5 volt connectors and boards are Keyed, so that 3.3 volt cards may not be inserted. The +3.3 volt boards are also Keyed but in a different location on the connector, so that 5volt cards may not be inserted. However the difference between the two card types resides with the signaling protocol they use, and not with the power rails. Refer to the PCI Bus Pinout page for signal descriptions and connector pin-out information.

As shown on the PCI page a half size card does not have to consume the entire card size defined, it may be shorter than allowed.
The same is true for either card size. The dimensions are maximum, so a smaller board is permissible.
A PCI board needs to conform to the dimensions up to the end of the expansion connector, so the fingers line up.
Un-used board space after the expansion connector could be omitted to save money.

Site Navigation; Index > Interface Buses > PC Buses > PCI Bus > PCI Card Dimensions

Related topics;
The main discussion of the PCI Bus interface.
Or see the related page on Manufacturers of PCI Boards for OEM vendors.

PC motherboard

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Modified 12/27/11
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