What is a Low-Profile PCI Card?


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What is the definition of a low-profile PCI card? What are the electrical and mechanical differences between a low-profile PCI card and a standard PCI card?

Low-profile PCI cards are PCI cards based on a new card size standard. The low-profile PCI design was developed to standardize the design of PCI cards used in small-footprint systems. Low-profile PCI cards follow the PCI Local Bus Specification, Revision 2.2 or later, but in addition adopt the form factor requirements of the new "PCI Engineering Change Notice (ECN) by the PCI SIG Group".

Electrical

Low-profile PCI cards (also known as LPPCI or half-height cards) have the same signal protocol, electrical definitions, and configuration definitions as standard PCI cards. Just like standard PCI cards, low-profile PCI cards use the 3.3 volt PCI slot. All low-profile PCI cards are electrically backwards compatible with any otherwise compliant PCI slot.

Mechanical

The low-profile PCI card standard has added new mechanical card height and depth specifications to the existing PCI Local Bus specification, Revision 2.2. This standard was adopted in late 2000 as an Engineering Change Notice by the PCI SIG Group.

What is a Low-Profile PCI Card?

There are two defined standard lengths for low-profile PCI cards under Revision 2.2, known as MD1 (can accommodate 32-bit cards) and MD2 (can accommodate either 32-bit or 64-bit cards)

MD1 low-profile card dimensions

MD1 defines the shortest 32-bit PCI card length, 119.91 mm (4.721 inches) and a maximum height of 64.41 mm (2.536 inches) including the edge connector.

MD2 low-profile card dimensions

MD2 defines the maximum length of a low profile PCI card as 167.64 mm (6.600 inches) and a maximum height of 64.41 mm (2.536 inches) including the edge connector. Any low-profile PCI card longer than the MD1 length is considered an MD2 card. MD2 is the most common low-profile card form-factor. Beside standard PCI, many PCI Express cards are often described as MD2 low-profile form-factor.

Low-profile PCI cards bracket and retention screw dimensions

Low-profile PCI cards have a reduced bracket height of 79.2 mm (3.118 inches), and the retention screw has also been moved 1.35 mm closer to the fold in the bracket. Due to the height difference of the metal retention bracket, low-profile PCI cards do not securely insert into standard PCI slots. The smaller bracket will not fit a standard desktop, tower, or 3U rack-mount PC case, but will fit in many newer small form-factor (SFF) desktop cases or in a 2U rack-mount case. National Instruments does not sell a bracket adapter that allows low-profile PCI cards to remain securely fastened in standard PCI slots.

Standard (full-height) PCI cards dimensions

For comparison, standard (full-height) PCI cards have a specified bracket height of 120 mm (4.70 inches) and a card height of 107 mm (4.20 inches). This height includes the card edge connector. Two lengths have been defined for full-height cards, known as full-length and half-length.

Full-length PCI cards have a specified length of 312 mm (12.283 inches), and half-length PCI cards are specified as having a length of up to 175.26 mm (6.9 inches). Most modern cards are half-lengths, because full-length cards cannot fit in many modern PC cases. The actual dimensions of many cards described as half-length full-height are lower than these maximums and they will fit any standard full-height PCI slot as long as they use a properly located full-height bracket.

Actually there are three different kinds of PCI cards: Full-Length, Half-Length, and another type called Low-Profile or Slim.

The bus connection is identical for all three types of cards, but most computers will only accommodate half-length PCI cards. You will need to check with the computer manufacturer or take a look at the machine specifications to verify what PCI size your computer can accommodate. The measurements of each PCI format are listed in the table below.

What is a Low-Profile PCI Card?