Talk:PCI Express/Archive 2007

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External

Blackmagic Design's Multibridge Extreme appears to implement external PCIe. The device itself is housed in a 1U rackmount and cabled to a card comprising nothing but a 4-lane PCIe edge connector wired to what looks very much like a DVI connector. It's visible on their website:

http://www.blackmagic-design.com/products/multibridge/

Whether this puts the lie to the "External: No" part of the page, or whether this is an unofficial application, it's clear that someone has implemented external PCIe.

The Multibridge Extreme is a device that uses PCIe to connect to the computer. The card that it uses is not simply a card that creates "External PCIe" It is an adapter for the use of Blackmagic Design. Jvc3po 17:51, 15 February 2007 (UTC)

General Compatibility

I'd heard that PCI-E is "backwards compatible" with PCI. When I got my new computer with PCI-E, I wanted to keep one of my old PC cards, but it would not physically fit: the PCI-E slots have a space between the pins near the panel side that the PCI card I wanted to keep didn't have a matching gap for, so it could not go in the slot. However, I checked some of my other PCI cards, and some of them did have that gap and did fit. Now, I want to buy a new card (USB2 & Firewire), but the only PCIe cards available so far cost a lot, and I'm fine with a PCI card (speedwise), but since my old one didn't fit, how can I tell if a new one will fit? I'm not looking for someone to directly answer my questions on Wikipedia, I can find a forum for that. It's just that there's no section addressing compatibility with PCI cards, I expected to get some info on this here, if anyone could add it.

-Tom, June 6, 2006

PCI-E is NOT backwards compatible with PCI PERIOD, the software layers may be the same but the physical interface is totally different. BTW the intro to this article reads rather like a marketing peice. Plugwash 23:11, 15 June 2006 (UTC)

This is exactly the question I came looking for, as a confused owner of 4 pci-e slots. Someone who understands this stuff enough to be writing about it should add this info and an explanation as to why to the main article. -Josh March07

Practically speaking if you want to use those slots you will have to find PCI express cards that give you the functions you want. Soloutions do exist that will let you connect pci cards through a pci-e slot (see for example http://www.magma.com ) but you will have to pay through the nose for them.

BTW be carefull not to confuse pci-e with pci-x (as it looks like the initial poster of this section may have done) Plugwash 21:59, 25 March 2007 (UTC)

Help with 'conversion'

"As it is based on the existing PCI system, cards and systems can be converted to PCI Express by changing the physical layer only – existing systems could be adapted to PCI Express without any change in software." Does this mean a PCI slot can support a PCI-express card? Or do you have to have a PCI-express slot that could possibly support an older PCI card? I'd like to get a new video card, but the one I want is PCI-Express, while I only have PCI-X slots. EDIT: I think they're PCI-X slots, but I'm not completely sure on if they are or how to find out. PirateMonkey 02:18, 28 January 2006 (UTC)

The slots are not compatible in any way. I presume the new PCIe slots were designed to make it impossible to insert old PCI cards. That section is simply saying that there needs to be no change in the software interface. Makers of PCI cards/chips can make a PCIe version by changing the physical interface and the card will work in a PCIe system. The system still sees a host bridge, one or more buses behind it, and devices with vendor:device ID's. No massive change to the way that works, except for graphics cards moving from AGP. Imroy 06:05, 28 January 2006 (UTC)

I just spotted some stuff at http://www.mobl.com/expansion/products/pcie_expansion/index.html for using PCI cards with a PCIe system, they are bloody expensive though. Plugwash 12:01, 12 March 2007 (UTC)

I believe that this fits here best, is there any way to simply add a PCI-E slot to your motherboard? -annonymous —The preceding unsigned comment was added by 68.99.190.230 (talk • contribs) 00:58, July 22, 2007 (UTC)

Not in any way that is at all practical. If the motherboard chipset doesn't support PCI-Express (and if you don't have the slots, it doesn't), you would need to provide your own controller and somehow interface it with the motherboard. — Aluvus t/c 09:51, 22 July 2007 (UTC)

In principle there is no reason why not, you can bridge PCI and PCI express in either direction. However such a product would be pretty pointless since you would still be restricted by the speed of the PCI bus. My google searches turns up lots of stuff from semiconductor manufacturers suggesting that such cards are a possible use of thier products but noone making the actual cards. Plugwash 10:15, 23 October 2007 (UTC)

adaptors

i guess an adaptor could theoretically be made to fit a card into a smaller slot then intended but there would be physical issues with the machines case in doing so. Would that be a correct analysis? Plugwash 23:15, 15 June 2006 (UTC)

Yes that would be correct. The added height would cause physical problems. There are companies that make "shims" to convert to lower lane widths. They are useful for testing.

got any names of such companies? a quick googling doesn't seem to be finding any. Plugwash 20:14, 17 January 2007 (UTC)

250 MiB or 250 MB

It is definitely 250 MB/s.
It's 1.25GHz * 2 bits/clock / (10 bits/byte) = 250 million bytes per second = 250 MB/s
To quote the IBM Redbook (see Link in the article):

"The 8b/10b encoding essentially requires 10 bits per character, or about 20% channel overhead. This encoding explains differences in the published spec speeds of 250 MBps (with the embedded clock overhead) and 200 MBps (data only, without the overhead)."

And especially to DmitryKo: If 2.5 Gbit/s was the real data bandwdith, you'd get 298 MiB/s and not 250 MiB/s.
I hope that's proof enough for you. If not, please show me how to get 250 MiB/s with a clock of 1.25GHz, DDR and a 8b/10b encoding. In my opinion, this is a calculation you should have done before changing the MB to MiB.
JogyB 21:22, 27 August 2006 (UTC)

• I just didn't realize bus bandwidth is expressed in decimal units... sorry. --Dmitry _{(talk •contibs )} 06:22, 28 August 2006 (UTC)

Nothing said above really matters, since some retardo has erroneously changed all the units to megabits, when they clearly should be bytes. The article which is cited as source 1 does talk about bits, but it is also wrong in doing so. —Preceding unsigned comment added by 84.248.78.243 (talk • contribs)

It looks like the intro was already reverted the change from bytes to bits, i have now removed the dubious reference that caused that change in the first place. Plugwash 20:44, 2 February 2007 (UTC)

splitting

is it feasible to have a splitter card that plugs into one PCI-E slot and routes different lanes to different cards? Plugwash 15:37, 2 December 2006 (UTC)

I assume not. A "link" is made of one or more "lanes", and the data is interleaved when a link has more than one lane. So I'm thinking it simply wouldn't make sense to split one link into its constituent lanes and use them separately. It would be like splitting up the 32 bits in the original PCI bus. Those bits/lanes are meant for one device. Perhaps you're thinking of a bridge? --Imroy 18:08, 2 December 2006 (UTC)

No, it is not a bus in the traditional way. You can do some magic with interrupt lines and use a bus expander card on standard PCI, but PCI Express is a whole different beast. For all effective purposes, it is a point to point protocol. — RevRagnarok ^{Talk Contrib} 15:04, 3 December 2006 (UTC)

I take that back. A "non-passive" card with an active PCI Express hub chipset may be able to do it, similar to a USB hub. But you would be limited by the "upstream" bandwidth so would need a x16 slot to handle two x8 peripherals. I'm not sure about addressing either, the downstream cards would have to split an address space. May get quite ugly, but probably possible - you'd have to pay me a lot to design one. ;) — RevRagnarok ^{Talk Contrib}

hmm, at what stage are the lanes on a host controller assigned to links? does it happen at chip design time? bios design time? or is it discovered at boot time? the last possibility would allow splitter cards. Plugwash 20:07, 8 January 2007 (UTC)

As for addressing wouldn't an active splitter card just appear as a PCI-PCI bridge with a new bus number for the slots behind it? Plugwash 17:59, 9 March 2007 (UTC)

Hotplugging

i see someone changed yes to no in the infobox for hotplugging and was reverted, the body text has no mention of this issue, so four questions.

• does PCI express support hotplugging?
• is support for it required or is it some obscure optional part of the spec?
• is support for it in major operating systems?
• how does this tie in with its software compatibility with PCI? —The preceding unsigned comment was added by Plugwash (talk • contribs) 15:17, 29 December 2006 (UTC).

As far as I know:

• Yes, it does.
• It depends on the form factor; for the common card form factor, it's optional (it needs extra hardware on the slot).
• I know Linux supports it; a quick google search shows Windows also seems to support it.
• PCI also has hotplug; I have no idea if an older OS which does not understand PCI Express would be able to work with its hotplug.

--cesarb 01:07, 2 February 2007 (UTC)

AGP

according to our AGP article the fastest variant of AGP that is listed has a maximum data rate of 2133 megabytes per second. PCIe after taking account of 8b10b encoding but not of higher level overheads (which is the figure most comparable with the headline figures for older paralell busses) with 8 lanes runs at 2000 megabytes per second. That sounds close enough to me. Plugwash 13:41, 16 January 2007 (UTC)

Now if there was an AGP 16x that would change things but i'm pretty sure there isn't Plugwash 13:48, 16 January 2007 (UTC)

Hot Plug Footnote

The standard footnote tag is not functioning properly with symbols, or the table messes it up. - MSTCrow 00:47, 2 February 2007 (UTC)

Hotplugging

Why is the table currently listed as hotpluggable depending on form factor? PCI-Express is always hotpluggable. How easy it is to actually access the card for removal or insertion is another issue altogether. - MSTCrow 03:28, 2 February 2007 (UTC)

AFAIK, when it's using the traditional card form factor, whether it's hotpluggable or not depends on extra hardware on the slot (the presentation I added to the external links has the details). That hardware is not always present. I also do not know whether the PCI Express Mini Card is hotpluggable or not. (Of course, if someone does have access to the actual standards, feel free to correct me.) --cesarb 14:51, 2 February 2007 (UTC)

Well, try this, a book everyone should have on their shelves (if not, go buy it). Scott Mueller's Upgrading and Repairing PCs, 17th Edition, Chapter 4, page 376, second to last bullet. - MSTCrow 00:15, 4 February 2007 (UTC)

But what the heck is it?

This opening paragraph is all fine and good...

PCI Express... is an implementation of the PCI connection standard that uses existing PCI programming concepts, but bases it on a completely different and much faster full duplex, multi-lane, point to point serial physical-layer communications protocol. PCI Express was formerly known as Arapaho or 3GIO for 3rd Generation I/O.

but it's lacking on what what the heck PCI Express actually is. (I mean, I personally know, but I fear readers unfamiliar with the finer aspects of computer hardware will not). The rest of the article is rather confusing also. I added an "unclear" tag. Hopefully someone with greater knowledge than myself can clear this up for the mortals. Sloverlord 01:25, 7 February 2007 (UTC)

I have attempted to to so. The articel still needs help, especially as it starts to describe things (EG. "lanes") well before it goes into details of what they are. 68.39.174.238 15:06, 10 February 2007 (UTC)

Missing/Incomplete info in Sidebar

I was comparing the various bus systems (ISA, PCI, AGP, PCI-X, PCI-E) and all but PCI-E has "Width:" and "Speed:" defined. Even if PCI-e (or is it PCIe) has multiple values for these fields, could they not all be listed to provide conformity with the other bus sidebars? Maetrix 17:52, 14 March 2007 (UTC)

First things first PCI express is not a bus, neither is AGP for that matter. PCI express is based on point to point serial links with an encoding that embeds the clock not on a paralell set of data lines with seperate control lines. Plugwash 20:33, 15 March 2007 (UTC)

That is clearly noted in the article, but it's still called a bus. — RevRagnarok ^{Talk Contrib} 01:23, 16 March 2007 (UTC)

pointless overuse of jargon

As an independent IT consultant of a great many years, I get a little tired of keeping up to date with the latest developments and latest acronyms.

Wiki, on the whole has proved to be an invaluable reference source on any number of subjects and serves primarily to clarify more complex concepts for the average reader who has no background in a given specialised field.

I read that this article has been criticised as being unclear. I agree wholeheartedly. It is written by a technical expert for comprehension only by other technical experts who are conversant in the latest set of acronyms and technologies.

I have read articles within Wiki's bounds about extremely complex subjects such as can be found within the general doomain of molecular biology and the quality and expertise of the author of the article has been so good that I have been able to understand the rather obtuse subject matter.

This article on the other hand serves only to make what is a fundamentally straightforward concept utterly confusing, but manages to dazzle the reader with more jargon and buzz-words per sentence than any article I have ever read on any computing related matter. In other words I believe the article was written to impress, not to clarify anything whatsoever, certainly not for a 'lay' reader. Furthermore I found the article unbelievably boring. It was like eating a diet of undercooked bread with nothing on it - stodge and more stodge, and had to give up reading halfway through because my head hurt from mentally translating all various jargon words and concepts which had been dragged in to the 'explanation'.

I believe that the purpose of Wiki is to make technically specialised subjects comprehensible to a person who has no specialisation within the given field. By this reckoning I believe the article is overdue for a complete replacement or alternate. I'll see what I can do also. Aethandor 11:27, 3 April 2007 (UTC)aethandor

a few revisions

The opening paragraph was somewhat unapproachable and it went downhill from there. I have revised it to try to make it a bit clearer. I moved the reference to development names to the bottom of the opening section as it serves only to confuse (like those people who insist on coming up with 'did you know that....' asides) when presented right at the outset of the article.

The original article dived into to talking about PCIe 1.1 without making any reference to standards bodies (PCI-SIG) or any reference to where the '1.1' had suddenly come from and I have added a section to provide this information before it is otherwise referred to.

The initial opening paragraph mentioning bridging but implied PCI to PCIe bridging (but conversely made no reference to SLI) which is wrong and I have removed this incorrect information.

To be honest much of the opening section is still hard to chew and it would read better if written with a view to explaining to ones' Grandmother rather than writing in a style of trying to justify oneself to Bill Gates. Phrases such as "PCIe is a flexible hybrid serial-parallel interface format.", "it uses serial interconnects which can be arbitrarily linked together" and "PCI Express is both full duplex and point to point" seem to take glee from the complexity and perversity of the concepts which aren't really being explained. I will look further into clarifying these if no-one else beats me to it. —The preceding unsigned comment was added by Aethandor (talk • contribs) 14:08, 3 April 2007 (UTC). Aethandor 14:09, 3 April 2007 (UTC)Aethandor

Can you put a 1x card in a 4x or 16x slot?

Can you put a 1x card in a 4x or 16x slot? Can you put a 4x card in 16x slot? 12.11.149.5 21:42, 9 May 2007 (UTC)

From the article

A PCIe card will physically fit (and work correctly) in any slot that is at least as large as it is (e.g. an x1 sized card will work in any sized slot)

In other words yes with no change in speed since the card supports only 1x PCIe. Phatom87 16:32, 10 May 2007 (UTC)

Incorrect statement regarding x16 not fitting in an x4 slot

From the article:

It is not possible to place a physically larger PCIe card (e.g. a 16x sized card) into a smaller slot, even though the two would be signal-compatible if it were possible.

This is not true. I have an ASUS A8N-E motherboard. An x16 card will fit and work in the x4 slot. It will just have a quarter of the bandwidth. However, the x16 card will not fit in the x1 slot. I'm sure other motherboards have similar designs. I'm not sure what it should be changed to, but it should be changed.

Also it should be x16 not 16x.

As explained in the introduction a 16 lane card WILL NOT fit in an 4 lane slot but it WILL fit and work in an 16 lane slot that only has 4 lanes connected.

reading that manual that board you link has a non-standard slot with a gap in the back, this means it will work with some larger pci-express cards but missing power pins may pose a problem. Plugwash 20:10, 29 May 2007 (UTC)

Are we talking about te standard here, or about te implentation of the standard? It seems we're doing te latter, while we're considering the former. I've read on several places that the standard should be capable of accepting cards that were deigned with more lanes in mind than there are available to them, and they should still work if both the motherboard and card were implemented by spec. (ocf81 07:36, 5 September 2007 (UTC))

PCIe v2 cards in V1 slots, compatibility ?

Do/will v2 cards work in v1 slots ? --Xerces8 15:10, 5 June 2007 (UTC)

Not necessarily. The more popular version, PCIe v1.1, is compatible with v2 but the earlier editons, v1.0 and v1.0a, are not compatible. As far as I know, there are no software updates available to resolve the incompatibility - a v1.0 board must be replaced if you want to use a v2 card. Efeinberg (talk) 21:33, 23 December 2007 (UTC)

Agree with the above

"Overview" and especially "hardware protocol summary" are just terrible. The latter especially looks like it was plagairized from some specification sheet. Anyone else want to just remove it and let it slowly rebuild, hopefully in an understandable manner? 68.39.174.238 09:19, 11 July 2007 (UTC)

I don't like this page...

...I find it frankly useless. It obsesses over minute details of the protocol while failing to explain why those matter or even what the point of most of this is. Look, for instance, at ISA or PCI: Both have technical detail, but with a well-organized system of headings and not so much as to overwhelm the more general information. 68.39.174.238 16:07, 17 July 2007 (UTC) (Rewritten 00:45, 11 November 2007 (UTC) to cool it down some)

Graphic Card only PCI-E slot

There should be some discussion that many motherboards with PCI-E will only let graphics cards be used in their x16 slots. This is a common problem people are facing w/ P35 based motherboards. —Preceding unsigned comment added by 24.199.118.101 (talk • contribs)

Do you have a source for that claim? Plugwash 20:14, 4 September 2007 (UTC)

How about open ended slots?

If a PCI-E slot had the forward end (towards the middle of the motherboard) open, then any PCI-E card could be plugged into any PCI-E slot. All the slots I've seen so far just have the one key near the back of the motherboard. That'd take care of preventing the card from slipping lengthwise in the slot. To reinforce that end of the slot, change the connector to have a pair of buttresses at that end with either plastic pins to go through holes in the board and melted or metal pins to solder. I bet if one got creative and VERY CAREFUL with a cutoff wheel and a Dremel... —Preceding unsigned comment added by Bizzybody (talk • contribs) 08:35, 8 October 2007 (UTC)

Afaict the result of cutting open the back end of a connector would be nonstandard (lacking power pins that should be there) but would probablly work in practice provided nothing obstructed the card. I really don't understand why they didn't make slots open ended as standard but they didn't. You could also modify the card instead of the motherboard cutting off the unwanted part of the edge connector. Plugwash 08:47, 8 October 2007 (UTC)

BTW while looking arround for something else I found a company selling adaptors to let you put bigger cards in smaller slots ( http://www.orbitmicro.com/global/pciexpresspciebusadapters-c-33_168_179_182.html ) , some case/card backplate modding may be required though. Plugwash 10:10, 23 October 2007 (UTC)

Uhh.. huh?

The current article suggests that a PCIe 2.0 card will not function in a 1.0 or 1.0a slot. I believe this is wrong, despite the above claim. http://www.pcisig.com/news_room/faqs/pcie2.0_faq/ suggests otherwise, and I personally know many people who are currently running a 2.0 card in a 1.0(a) slot. Hell all you have to do is google around, I haven't been able to find a single bit of documentation concerning forward or full incompatibility. If anything, only a certain (small) number of motherboards sport this incompatibility, or it's just a rumor. I'm not going to edit the article, because I'm a wiki noob, and I could very well be half wrong. 76.27.231.157 (talk) 03:24, 28 December 2007 (UTC)

Repost :o