Physical card dimensions
The original “full-size” PCI card is specified as a height of 107 mm (4.2 inches) and a depth of 312 mm (12.283 inches). The height includes the edge card connector. However, most modern PCI cards are half-length or smaller (see below) and many modern PCs cannot fit a full-size card.
In addition to these dimensions the physical size and location of a card’s backplate are also standardized. The backplate is the part that fastens to the card cage to stabilize the card and also contains external connectors, so it usually attaches in a window so it is accessible from outside the computer case. The backplate is typically fixed to the cage by either a 6-32 or M3 screw, or with a separate hold-down bracket.
The card itself can be a smaller size, but the backplate must still be full-size and properly located so that the card fits in any standard PCI slot.
Half-length extension card (de facto standard)
This is in fact the practical standard now – the majority of modern PCI cards fit inside this length.
- Width: 0.6 inches (15.24 mm)
- Depth: 6.9 inches (175.26 mm)
- Height: 4.2 inches (106.68 mm)
Low-profile (half-height) card
The PCI organization has defined a standard for “low-profile” cards, which basically fit in the following ranges:
- Height: 1.42 inches (36.07 mm) to 2.536 inches (64.41 mm)
- Depth: 4.721 inches (119.91 mm) to 6.6 inches (167.64 mm)
The bracket is also reduced in height, to a standard 3.118 inches (79.2 mm). The smaller bracket will not fit a standard PC case, but will fit in a 2U rack-mount case. Many manufacturers supply both types of bracket (brackets are typically screwed to the card so changing them is not difficult).
These cards may be known by other names such as “slim”.