PCI-e slot dumb question

[goombawaho]

Can you take a look at the following document, Page 7, Table 3 to be precise

http://i.dell.com/sites/content/business/solutions/whitepapers/en/Documents/wp-2004_pciexpress.pdf

and tell me what the difference is between REQUIRED and ALLOWED in terms of interoperability and/or performance. I certainly understand what NO means (non-compatible).

The background is that I'm looking at a RAID controller (Adaptec RAID 1430SA) that is X4 and a Dell server that has X8 and X1 slots.

 

[ponoodle]

I think what they mean is for the card to run at its native speed (or the slot's), it "requires" the same type. If the card will work, but at a lower speed than the card (or the slot), then it is "allowed" to be used in that slot. They just run at the lower speed.
My other thought is that the person who wrote this should be REQUIRED to take some classes before they are ALLOWED to write another doc.

 

[vacunita]

I'm thinking the "required" sections for the 1x cards should be "allowed" for all slots except the 1x slot which would be required at the very least.

for everything else, it makes sense that you require at least the speed of the card, but are allowed slots with higher speeds.

Only certain 8x cards can be placed into certain 4x slots but will operate at lower speeds.

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[rclarke250]

It means that a x1 card will work in any slot, A x4 card will work in all slots at rated speed except x1 slot, a x8 card will work in a x8/x16 slot at speed, but at a reduced speed in x4 slot that has a x8 connector on the motherboard. and a x16 card will only work in a x16 slot.

 

[BadBigBen]

OK, this is how I interpret it...

the ALLOWED with the ASTERIK, is the only ODDBALL in the lot, meaning that if a PCIe 4x is coupled with an 8x slot, that it will allow any 8x card to run at reduced speed...

all other ALLOWED, should actually be called REQUIRED, as the cards will run at FULL speed...

basically what the rest said, a 1x card will work in all PCIe slots at full speed.

a 4x card will run full speed in 4x, 8x, and 16x slots.
a 8x card will run full speed in 8x and 16x slots. except where the 8x slots are hardwired as 4x speed, the mainboard manual should mention this...
and a 16x card will run full speed in a 16x slot, except when there are two slots, then it may only run at 8x speed if the other is populated... also the manual should mention this fact...

and that mentioned RAID controller, should work FULL speed in all slots except the 1x slot (as insertion is not possible)...



Ben
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[goombawaho]

Ok, thanks. I understood about the oddball 4x in an 8x slot, but the verbiage was getting me on the others.

So, in all circumstances if I pick either an x1 or an x4 PCIe card, it will run full speed in the X8 slot of the server.

I hate to say that I've done precious little with PCIe add-on cards. Most things I deal with are A) Old, so not too much PCIe AND/OR B) Everything is integrated on the server/PC mobo.

In the old days 2000 - 2004, everything was an add-on PCI card (SCSI controllers come to mind) to which I attached all my little SCSI hard drives with their big old ribbon connectors. Fun times. No hot swap, jumper pins had to be set for SCSI ID.