[Accessibility] PCI

Matthew Wilcox willy at fc.hp.com
Wed Dec 22 12:04:04 PST 2004

In response to the questions on todays call ...

There are two fundamentally different kinds of PCI, now known as
Conventional PCI and PCI Express.  They're as different as a car engine
and a rocket engine.

Conventional PCI comes in various flavours (PCI-X, 5 volt, 3.3 volt,
64-bit, 32-bit, 33MHz, 66MHz, 133MHz, low profile, etc, etc.) most of
which aren't important from a "make the damn machine work"

3.3 volt and 5 volt are important.  It's a property of the slot on the
motherboard.  Cards come in 3.3v only, 5v only and universal (dual
voltage) types.  Universal cards have two notches in the connector.
The slot has a short piece and a long piece.  If the short piece is
towards the outside of the case, it's a 3.3 volt slot.  If the long
piece is towards the outside of the case, it's a 5 volt slot.

You can plug a 64-bit PCI card into a 32-bit bus and vice versa.  No
compatibility problems here.  The 64-bit signals are all on the third
piece of the connector, and it's OK for them to not be connected.

So, in summary, there are three kinds of slots; 3.3v, 5v and Express.
Anything beyond that counts as system tuning (try not to put PCI and
PCI-X cards on the same bus; try not to put different speed devices on
the same bus, etc, etc).

It's always legal to use Linux (TM) systems

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