PCI-E question.

[JetUsafMech]

With all the improvements that pci express brings, does this mean true u320 will be had on the desktop? What I mean is, currently, an u320 card is limited by the pci bus to 160, but with pci express being independent, and backwards compatable, the full 320 should be realized, right?

 

[big daddy fatsacks]

huh? what do you mean U320 is limited to 160?

 

[JetUsafMech]

I thought that in order to use a 320 drive in a normal pci mobo, the card, even though it may be 320, was limited to 160? Or am I mistaken? I'm the first to admit that I'm no scsi god, so please correct me, just trying to learn!

 

[Ice Czar]

the typical desktop has a 32bit 33MHz PCI bus and is limited to 133MB/s

whereas current workstation\server class bandwidth is as follows
64bit 33MHz 264MB/s
64bit 66MHz 512MB/s
64bit 133MHz 1 GB/s (PCI-X)




SCSI U320 just describes the interface capacity
and has nothing really to do with the internal performance of the HDD, put another way the SCSI controller would be able to employ 320MB/s through a PCI bus that was at least that large, if enough HDDs where connected to it and that level of access was attempted. A single SCSI HDD wouldnt even come close, and you probably dont own an application that would do it either, generally speaking it requires a multi-user environment, even CAD\graphics ect, have great difficulty saturating 320MB/s

http://www.machinedesign.com/ASP/strArticleID/55541/strSite/MDSite/viewSelectedArticle.asp
http://www.interfacebus.com/Design_Connector_PCI_Express.html
http://www.interfacebus.com/Design_Interface_table.html
http://www.compute-aid.com/64bitpci.html
http://www.hardforum.com/showthread.php?s=&threadid=699246 > specifically > http://www.lostcircuits.com/hdd/hdd4/ > Interface Speed as Basis for Classification

more than likely any SCSI controller you currently have will not be compatible with ePCI
PCI-X however is backwards compatible

 

[JetUsafMech]

Ice Czar--thanks for the links. It looks to be a very interesting year with the emergence of pci-e, btx, etc (though it looks that none will be mainstream for awhile). I remember a couple of years ago when Amd's Hypertransport and Intel's 3GIO were first mentioned. My question was about the interface, since pci-e will have more bandwidth than pci-x, as I read it (correct me if I'm wrong), shouldn't a pci-x scsi card be....I guess "forward compatable" with pci-e and utilize the cards potential? I think I'm getting over my head...lol. Thanks!

Found this link helpful also:
http://www.intel.com/technology/pciexpress/devnet/docs/WhatisPCIExpress.pdf


I'm beginning to think I should've posted this in the mobo section...sorry.

 

[Ice Czar]

Originally posted by JetUsafMech
shouldn't a pci-x scsi card be....I guess "forward compatable" with pci-e and utilize the cards potential?

nope note the physical differences
http://www.machinedesign.com/ASP/strArticleID/55541/strSite/MDSite/viewSelectedArticle.asp

"In contrast to the old PCI, PCI Express is based on serial differential links rather than a parallel bus. Zero crossings of differential signals, rather than rising edges, are used to denote logic levels. The differential signal is derived from the voltage difference between two conductors. This scheme works well with the sub 5-V logic levels found on today's circuitry.

Another key facet of PCI Express is that is can be deployed in multiple widths, unlike old parallel bus schemes that had one fixed set of signals. The reason is that PCI Express is a serial architecture. Data bytes get transmitted sequentially over one or more four-wire lanes. A given PCI Express connection can hold up to 32 separate lanes of four wires each. Thus PCI Express actually consists of multiple independent serial connections grouped together."

http://www.eetasia.com/article_content.php3?member=no&article_id=8800303971&DD=c040508b

"This seamless migration to PCI-X 2.0 is in sharp contrast to the discontinuity that would occur in a move to Express. Without backward compatibility of the slot/adapter, Express will not easily replace PCI slots in servers. Adapter vendors would need to provide two separate product lines during the transition, and server vendors would have to provide multiple servers with different mixes of PCI and Express slots to satisfy customers in various stages of transition. Customers would, for the first time in 10 years, have to manage deployment of incompatible adapter types among their servers. "

alot of it is still up in the air
(From the first link again)
"Tyco Electronics Corp. connectors for x1, x4, x8, and x16 lanes (The spec reserves x2 lane configurations for cable connections rather than circuit boards). One concept for evolving to the PCI Express format is to devise plug-in boards with both ordinary PCI and Express connections. Plug-in boards could take advantage of Express on CPU boards that provide it; otherwise they would revert back to operation over PCI. Express's backward compatibility with PCI protocols makes this option possible."

"PCI Express board connectors will have widths of x1, x4, x8, and x16. Legacy PCI slots will probably sit next to native PCI Express connectors on most CPU boards initially. The serial nature of the PCI Express protocol will make it possible to plug smaller PCI Express cards into larger slots -- PCI Express circuits will be smart enough to discern that fewer lanes are connected, then configure themselves to handle what they find."



so hybrid cards are possible, but nothing youd have now would be forward compatible (see graphic at the bottom of the 1st link)

I remember a couple of years ago when Amd's Hypertransport

owning a Tyan K8W w\Dual 244s I can tell you HyperTransport is sweet