PCI/ISA Board Interface Combination
Four sizes of PCI add-in cards are defined: long, short, Low Profile, and variable short
length.
However; systems are not required to support all add-in card types.
Short Form PCI Printed Circuit Board Dimensions
Navigation; Index > Interface Buses > PC Buses > PCI Bus > PCI Card Dimensions
The standard PCI card form factor is 107mm x 312mm [4.2" x 12.283"]. The
standard card version is listed on the PCI Bus Card Size page.
The first graphic below shows a PCI bus with an additional PC AT [ISA] bus on the same PC board.
The PCI / ISA board differs from the board dimensions specified in the
PCI specification.
The next graphic shows a low profile PCI card.
The low profile version of the PCI board ranges from 64.41mm x 119.91mm to
64.41mm x 167.64mm [2.56" x 6.6"].
Four sizes of PCI add-in cards are defined: long, short, Low Profile, and variable short
length.
However; systems are not required to support all add-in card types.
The Peripheral Component Interface 'PCI' Bus was originally
developed as a local bus expansion for the PC (ISA) bus, and was coined
the PCI Local Bus. The spec started as an add-on to the ISA form factor
with the PCI requiring its own connectors. The PCI specification defines
the Electrical requirements for the 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 pin placement define how 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.
The top picture show a combination PCI/AT card; for reference, J1 (sides
A/B) represent the XT bus, J2 (sides C/D in addition to J1 A/B) represent
the PC AT (ISA) bus.
There is also another style of card called PISA; PCI+ISA (not
shown above). It's a combination ISA, and PCI bus in a short card form
factor. In PISA's case the ISA and PCI fingers are on top of each other
(but offset). You need a back plane designed to accept PISA cards, to use
the PISA card. The PISA bus is used as an Industrial Embedded Computer
Bus, not a consumer Personal Computer bus.
The card [Board] sizes shown do not represent the absolute card size
possible, but represent the general size which may be encountered.
The size of a PCI card is represented by the second graphic, which depicts a
PCI bus expansion card without the ISA bus.
Another drawing shows the actual card size as defined by the PCI standard and is found on the
PCI Card Size page.
Refer back to the main discussion of the PCI Bus description.
Also see the related topic of Manufacturers of PCI Boards
Of course the boards pins have to align with the connector pins on the Mother-Board, the max board size is a different matter.
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