ddrueding
Fixture
Why do we have these two formats? Why are servers coming out with PCI-X slots while desktop video cards are PCI-E? Which is technically superior and which is likely to succeed?
PCI-X and PCI-E: Why?
- Thread starter ddrueding
- Start date
I'm no authority on the subject, but here's what I've gathered:
PCI-X (Extended) is an upgrade from old PCI. PCI-X provides 64-bit IO @ 133MHz. (1 GBps)
There is also a PCI-X 2.0 which goes to 533MHz or something insane.
http://www.pcstats.com/articleview.cfm?articleid=1087&page=1
Anyway, the general gist I've gotten is that PCI-E is here to stay. Two different markets perhaps.
PCI-X (Extended) is an upgrade from old PCI. PCI-X provides 64-bit IO @ 133MHz. (1 GBps)
There is also a PCI-X 2.0 which goes to 533MHz or something insane.
http://www.pcstats.com/articleview.cfm?articleid=1087&page=1
Anyway, the general gist I've gotten is that PCI-E is here to stay. Two different markets perhaps.
PCI-X is simply an extension to the PCI bus. It adds MHz (33->66->100->133MHz) and/or extending the number of data lines (32->64). As an engineering task, going faster and adding more parallel lines to a bus becomes increasingly difficult to do. The crosstalk, impeadance, end-point reflection, and maintaining proper timing get harder and harder to do the faster the bus with the more parallel lines on an unterminated bus.
PCI-E is going to be the replacement of the PCI bus, in the long run. The long range solution to those problems that plague the PCI bus is to go serial with your data. Because it uses far less lines it will typically be cheaper to build. Because it is serial it doesn't have race conditions or crosstalk to deal with. All that matters is that you can get the speed way up there. Engineers have decided that it is easier to deal with a single very high speed line than deal with parralell lines.
That is the point of SATA replacing the parallel ATA bus and SAS replacing the parallel SCSI bus. The next step in the plan is for PCI-E to replace the PCI bus. They are all trying to solve the exact same problems by replacing a parallel bus with a high speed serial line with equivilent to superior BW with a potential of going way higher at a much less cost than a parallel architecture.
PCI-E is going to be the replacement of the PCI bus, in the long run. The long range solution to those problems that plague the PCI bus is to go serial with your data. Because it uses far less lines it will typically be cheaper to build. Because it is serial it doesn't have race conditions or crosstalk to deal with. All that matters is that you can get the speed way up there. Engineers have decided that it is easier to deal with a single very high speed line than deal with parralell lines.
That is the point of SATA replacing the parallel ATA bus and SAS replacing the parallel SCSI bus. The next step in the plan is for PCI-E to replace the PCI bus. They are all trying to solve the exact same problems by replacing a parallel bus with a high speed serial line with equivilent to superior BW with a potential of going way higher at a much less cost than a parallel architecture.
I just read what I wrote and am not particularly pleased with it. It needs editing to be more accurate. Even in its inaccurate state it still portrays the gist of what I wanted to get across. So I guess I'll live with it.
So please forgive any inacuracies or incompleteness of some of the statements. Or even better make posts that correct the inferior statements.
So please forgive any inacuracies or incompleteness of some of the statements. Or even better make posts that correct the inferior statements.
ddrueding
Fixture
So PCI-X is a brute-force kludge that is here to deal with excess demand on current technology, while PCI-E is a new architecture that promises higher speeds at lower costs (eventually). Do I have it right? Will servers eventually go PCI-E?
GIANT
Learning Storage Performance
ddrueding said:
No, PCI-X is definitely not kludge someone dreamed up overnight. The evolution of PCI from 32-bit / 33 Mhz clock was a well-planned evolution that began in the early 1990s. Exactly how the evolution transpired, was a bit different than what Intel planned. Certain vendors bumped the clock speed of 32-bit PCI to 66 MHz earlier than what Intel wanted as well as the jump to 64-bit / 66 MHz. PCI-X came along as an update, actually, where the fundamental signaling was tweaked for efficiency in favour of further elevating the clock speed.
PCI Express was not part of the original PCI evolution plan from the 1990s. PCI Express is essentially full-duplex serial PCI. PCI-E falls into the greater trend of serial data channels and busses; SATA, SAS, F-C, Firewire, USB, etc.
Yes, absolutely, and sooner than later. Full-duplex PCI-E will match up ever so beautifully with technologies like full-duplex HyperTransport and SAS. PCI-X is half-duplex.
sechs
Storage? I am Storage!
The reason why servers are still holding on PCI-X, while desktops are moving to PCI-E is entrenchment. PCI-X is a proven, stable technology with lots of cards. You don't want any big surprises in a high-availability server!
Dell is now incorporating PCI-E into their new low-end servers. That being said -- I'm not impressed. They are incorporating x8 and x1 PCI-E slots and the problem is that they are useless right now. They are using integrated video with no AGP slots; and the minimum standard for a PCI-E video card (for the most part the only PCI-E boards that exist) is x16.
I suppose eventually a network/SATA/SAS or another server-useful 8x PCI-e card will exist but not yet.
To me that shows that PCI-E is already invading the server market.
I suppose eventually a network/SATA/SAS or another server-useful 8x PCI-e card will exist but not yet.
To me that shows that PCI-E is already invading the server market.
ddrueding
Fixture
Sounds good to me. IIRC, a 1x card can run in any slot, but I thought a 16x card could run in a 8x slot @ 8x speeds?
No smaller cards get to plug into larger slots (x1 card into a x16 slot is ok)but you can't make a x16 card plug into a x8 slot.
The actual slots are different sized so you can't actually fit an x16 card (82 pins) into an x8 slot (49 pins). There is only one mechanical key in the slots and that is between pins 11 and 12 with no allocated keys for the edges of the connectors of smaller slots. Even if there were, you'd have problems with exposed pins (an exectronic no no)
The actual slots are different sized so you can't actually fit an x16 card (82 pins) into an x8 slot (49 pins). There is only one mechanical key in the slots and that is between pins 11 and 12 with no allocated keys for the edges of the connectors of smaller slots. Even if there were, you'd have problems with exposed pins (an exectronic no no)