PCI card dimension

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I have what seems to me to be a very basic question, but over an hour of
Google searching has failed to find any reasonable answer.

The question is simply this: What are the actual dimensions of standard PCI
cards? And of so-called "half-height" cards?

Although Wikipedia gives the dimensions of the official standard as height
107 mm (4.2 inches) and a depth of 312 mm (12.283 inches), looking at a
recent PCI card (it's a Sitecom WiFi card as it happens) and at the PCI
slots on the motherboard, I can see that although it is about the right
height, it is much shorter than this - about 120mm. This seems to be what
www.interfacebus.com call a "short" PCI card, but it's shorter than that -
they say that the "short" card is 174mm long. My motherboard has 3 PCI slots
and they all definitely won't take a card anything like as long as 312mm
(which is over a foot).

I have just bought a new PC which only takes "half-height" PCI cards
(although the so-called "specification" doesn't actually tell you this). I
am pretty sure that my standard-height, short PCI card won't fit. But apart
from the back-plate, the actual card itself if much lower than the full
height - about 67mm including edge slots.

Wikipedia just says that ""Half-height" and "half-length" cards and slots
are common, and presumably have dimensions half those of the full-size
cards". I think this presumption is wrong, I think that "half-height" is
just a way of saying "lower than full-height", and since half-height or
"low-profile" cards are available I guess this must be some sort of
standard. But, my question is, what sort of standard is it? What are the
standard dimensions of a "half-height" or "low-profile" PCI card, and will
my card fit if I remove the back plate?

An obvious way to find out is to try it and see. But surely somewhere there
must be a defined standard? Or is this too much to hope?

 -- Philip

Re: PCI card dimension

On Wed, 17 Jan 2007 11:46:36 -0000, "Philip"

Quoted text here. Click to load it

http://en.wikipedia.org/wiki/Mini_PCI ?

Kind regards,
Gerard Bok

Re: PCI card dimension

On Wed, 17 Jan 2007 11:46:36 -0000, "Philip"


Quoted text here. Click to load it

When buying a ready-made system, one cannot presume the
system adheres to standards rather than somewhat
proprietary.  Even so, there is still the reasonable
presumption it has to adhere to some of them just to make
(their) sourcing of parts cost effective, instead of having
to reinvent everything at significantly higher cost in
design and manufacturing (parts the OEM buys then uses).

The length can vary quite a bit depending on how the board
is laid out, situated in the case, but a useful working
number is about 120mm length of PCB from the forward edge of
the PCI slot, to rearward edge that screws to the mounting
bracket.  In other words there can't be anything blocking
the forward edge of the card when it doesn't extend forward
past the slot itself.

The height could be exceeded a few millimeters depending on
the design of the case, but another working number (I don't
recall if this is a spec # or not) for total PCB height
(including card edge) would be 65mm.  

As to whether your card will fit if you remove the
backplate, how will you then mount it?  It's easier to find
cards 65mm or less than to also find them with the back
mounting bracket, though I suppose you can machine down that
bracket to the height you need, or fabricate one though
often cards with so little on them that they'll fit on a
half height card, aren't very expensive if you had to find
an alternative with the shorter bracket included.

Some cards are shorter merely to save on cost of the PCB
material used, not necessarily targeted to fit a half height
standard, so you may find cards not much taller than 65mm
but still too tall to fit (like Promise Ultra/FastTrack 66
(not that you'd want to use one today but it's just an
example, a few years ago I ended up replacing the right
angle pin headers on a FastTrack66 with straight 180' header
and sawing off about 1 cm from a card so it would fit in a
low profile case... so it is possible to /make/ a card fit
sometimes, but more often the designer routed something up
nearer the top edge that can't be cut off)).

Re: PCI card dimension

Philip wrote:
Quoted text here. Click to load it


Low-Profile PCI

Q: What is Low-Profile PCI?

A: Low-Profile PCI is a new PCI card standard for space-constrained system
    designs. The new form factors maintain the same electricals, protocols,
    PC signals and software drivers as standard PCI v2.2 expansion cards.
    They are also mechanically similar; however, Low-Profile PCI is an
    additional form factor that defines a shorter raw card and new mounting
    bracket for card retention. The Low-Profile PCI definition is an engineering
    change notice (ECN) to the conventional PCI specification, Revision 2.2. It
    include a new section in the mechanical chapter to define the Low-Profile
PCI raw
    card and mounting bracket.

Q: What is the difference between Low-Profile PCI and Mini PCI?

A: Low-Profile PCI and Mini PCI are two different initiatives that address
    market needs. Low-Profile PCI will allow greater flexibility in desktop and
    designs, and in some cases eliminate the need for riser cards. Mini PCI was
    developed specifically for integrated communications peripherals such as
    and network interface cards (NICs) in a mobile environment. Mini PCI provides
    flexibility for OEM/system integrators and is not intended for end-user

Q: If Mini PCI is smaller than Low-Profile PCI, then why not use Mini PCI rather
    define a new standard?

A: The smaller card dimensions for Mini PCI require more compact and higher
    components than Low-Profile PCI. Mini PCI is a standard for integrated
    that targets small form-factor products such as notebook PCs, docking
stations and
    printers. In addition to the small size, Mini PCI requires a new interface
to the
    board and system. Low-Profile PCI leverages existing adapter-card designs.
    cards are already short in height to save cost and optimize PCB panel sizes.
In many
    cases, the bracket drives the height of the card assembly and therefore, the
    height of the system design.

Q: How tall will the Low-Profile cards be compared to standard PCI adapter cards?

A: Low-Profile PCI should fit into systems as low as 3.350" [85 mm] without the
    use of riser cards.

Q: Are there various card lengths defined for Low-Profile PCI similar to short
    long cards for standard PCI?

A: Low-Profile PCI has two card lengths defined for 32-bit cards, MD1 and MD2.
    purpose of MD1 and MD2 is to establish size limits for system designers. MD1
    the shortest card offering and poses the greatest challenge to adapter-card
    However, MD1 cards also allow for the smallest system design. Systems which
    designed to support both MD1 and MD2 card lengths will have the greatest
    in supporting all Low-Profile PCI compliant cards.

Q: Will Low-Profile PCI fit into current brackets?

A: Low-Profile PCI will be backward compatible for existing brackets; however,
    ECN will also define a new bracket that will not be compatible with standard

Q: Is Low-Profile PCI going to support 5.0 volt signaling?

A: To reflect the PCI-SIG's market recommendation of moving to 3.3 volt signaling
    as quickly as possible, Low-Profile PCI will only support 3.3 volt signaling.

Q: What is the status of Low-Profile PCI?

A: The Low-Profile PCI ECN was officially approved and released by the steering
    committee on February 11, 2000. The Low-Profile ECN, along with all other
    to the v2.2 PCI bus specification, are currently available at the PCI-SIG Web
    site, www.pcisig.com, for free download to the industry.

Q: When will Low-Profile PCI products be available?

A: Compliant Low-Profile PCI products are currently on the market. Q-Logic is
    presently producing Low-Profile PCI products. Accton Technologies is also
    currently producing two products that support Low-Profile PCI, the EN1207D
    series 10/100 Fast Ethernet Adapter and the EN1207F series 10/100 Fast
Ethernet Adapter.

The low profile ECN is here. I expect that at least some of the cards
you'll find, won't be entirely compliant with the intent of specs like
this. For example, the cards might not be 3.3V only, in the interest
of the company making them being able to sell more of them.


The MD1 is 4.8" long and MD2 is around 6.6". The 4.8" is probably selected to
meet the end of the motherboard connector.

For more info about PCI, use your favorite search engine and look for
It is a 3,837,952 byte file. Should it be available for download ? No :-)


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