Taking the Mystery Out of PCI-Express
For the last few years, computer designers have been quietly transitioning computer users into a major technology upgrade. This new technology changes the way motherboards [define] handle data from other components plugged into the I/O data bus [Input-Output]. A bus is a connection point between the CPU [Central Processing Unit] and computing devices consumers want to add to their equipment.
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Wonderful in theory ... but it doesn’t “work as advertised” ... “allee samee samee” as AGP video.
AGP video “offloads” video signals from the PCI Bus and does free up bandwidth for things like harddrive I/O, communications (notably network operations) but if you copy a group of files from C: to D: and at the same time from C: to F: (if F: is a USB external drive) and across a gigalan network connection to K: there will be a noticable slowdown versus only one of those operations.
Additionally the “true” bus speed will be either 30 or 33, not the claimed 60 or 66 mhz. Over the years there were some boards which had 37.5 and even 40 which had noticably faster throughput but any given PCI card might or might not function properly at the higher bus speed.
I recently bought a series of MB’s to evaluate which “flavor” to go to for a company-wide upgrade. I benchmarked typical tasks under both eCS (EComm Station, without all the bleeping overhead of Windoze) and the various Windows versions, mostly “Extra Krispy”.
One sample is an operation which involves displaying and saving to file 6000 full screen graphs.
AGP 8X takes 9 hours ... PCI-Express with 2 of the highest-rated ATI cards drops it to 8.
!!!BUT!!! on board video (which runs at FSB bus rather than PCI-anything or AGP) takes a bit under 3 hours.
Bah, humbug !!!!!!
Great in theory, in practice it’s as worthless as a 3 legged dog on a fox hunt.
Go to SATA instead.
But again there’s the “software limitations” over the hardware. There is virtually no advantage of SATA 300 over 150 outside that some 150 controllers can’t see driver in excess of 250 GB capacity, others see as data drives but can’t boot.
Under eCS there is a bigger performance difference.
Nothing new here, we went through the same thing with SCSI II versus SCSI III.
Thanks so much for the great info articles.
I’m learning at an advanced age and I enjoy it.
Enjoyed the article on PCI_express ports…
very good info and easy to understand..
the only problem I had is with it is the photo of the motherboard, and showing the 16X pci-e slot..
I could not see it in the photo.. it looked like the photo was cropped wrong..
Any way, just want to let you know I did enjoyed the article and keep up the gReat work..
Your tech-tips articles are generally pretty reasonable, but I have to comment on the latest on PCI-E which contains a couple of glaring mistakes. First, the PCI bus is not 8 bit wide, it is generally 32 bits wide with a 64 bit extension defined but not widely used. The bus width is NOT the limiting factor on PCI speed. The limits are due to time restrictions imposted by signal skew considerations and due to the fact that it is a multiple connection bus which results in additional timing and drive constraints. Using a largely serial bus eliminates the skew problems and allows speed to be increased greatly, enough to give a significant overall increase in spite of the much narrower bus. Since PCI-E is a radial “bus”, this eliminates the restrictions imposed on multiple connection buses and, as mentioned, allows simultaneous operation of devices.
Also, it might be reasonable to mention that this evolution to a radial architecture actually started with the introduction of the AGP slot, which is actually a modified PCI “bus” which only supports a single device.
The issues involved in determining the “best” way to interconnect a number of devices are interesting and the best solutions change as technology changes. A few hardware generations ago the multi-drop bus was the most cost effective. Today, logic is a lot cheaper and the cost of the additional logic needed to implement a faster radial architecture is not significant. Also, logic capable of handling very fast serial data is cheap. It did not exist a few years ago.
The comparison to a network router is at best misleading and at worse simply wrong, depending on how much you want to stretch the definition of “router”.
Providing simplified explanation of computer technology is a reasonable thing to do, but it should be correct.
Thanks, y’all are doing a great job and the TECH TIPS are really helpful and appreciated!
Excellent information, And not having to visit a lot of web sites to get it, is a bonus!
I truly appreciated the article on the PCI-E and found it helpful. I’m pretty computer savvy, building all of my machines - currently 4 operating on our local network, but I have found that I am now a step behind the latest technology. It has been 2 years since I built my last machine, and I am ready to build/upgrade at least 2 of them. I am just waiting to see what AMD does in response to Intel’s Duo Core. If it isn’t something special and economical, I will reluctantly go back to Intel for CPUs.
Please keep the information coming.
Your article was helpful in general but I’m not sure I follow you here (bold emphasis mine):
To solve this potential legacy problem, computer designers provided for a transition from traditional PCI to the new PCI-Express standard by designing motherboards with a combination of PCI and PCI Express connectors. Consumers can plug smaller connectors from PCI devices into the larger PCI-E host connectors on the motherboard. However, the newer PCI-E devices do not fit into the smaller sized PCI connectors.
Are you sure you didn’t mean to say that consumers can plug smaller *PCI-E* devices into larger PCI-E host connectors--in other words, a x1 into a x4, a x8 into a x16, etc.? I’ve heard that this is indeed a possibility.
And isn’t it true that ANY size PCI-E devices do not fit into the PCI connector, due to keyed sockets? Your final sentence above seems to imply that PCI connectors are always smaller than PCI-E devices, which makes sense for x16 connector but would also have to include the x1, x4, and x8 sizes that ARE smaller than the ol’ PCI connector, right?
Hope this helps,
Thank you Jack:
This latest tip has got to be the best article on understanding the PCI-E slots to date.
How can I find out which devices use the various types of PCIe levels, i.e., PCIex1, PCIex4, etc.?
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