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Re: PCI hardware

On Thu, 2003-08-14 at 11:35, vinai wrote:

> With the newer, faster flavours of PCI (PCI-X, etc) there might be some
> incompatibilities.  I've already heard rumblings about the new Apple G5
> machines only being able to use 3.3V "PCI" cards. But they run on a new
> flavour of PCI, and won't be able to use the older (5V) PCI cards.

Notice how the bottom edge of a PCI card has a notch or
two in it. Cards with two notches will tolerate both 3.3v
and 5v. Cards with one notch far from the place where you
plug in an Ethernet cable are 5v-only. Cards with one notch
near the place where you plug in cables are for 3.3v only.
You can also get 64-bit cards, with an extra bit of connector.
These are typically 3.3v-only AFAIK.

With the plug-side to the left:

============= ===     32-bit 5v-only
=== ========= ===     32-bit, any voltage (card only)
=== =============     32-bit 3.3v-only
=== ============= =======   64-bit 3.3v-only

What I mean by "card only" is that you don't see
multi-voltage slots. That would require a lever that
flips from one side to the other or a cover that
snaps back and forth over the slot -- this to both
signal the motherbard and physically prevent you
from exposing a card to the wrong voltage.

PCI-X is a protocol change. If all the cards on a
bus are capable of doing PCI-X and the motherboard
like it too, then the bus can run the PCI-X protocol.
PCI-X seems to be a requirement for exceeding 66 MHz.

Sometimes you get several kinds of slots in one system.
I just got an x86-64 box at work with a regular 5v slot
and 5 wide 3.3v slots that can do PCI-X, some of them
to 133 MHz.

When buying a new card, favor a choice that lets you
run at both voltages.

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