PCI-Express Video
Ready for business applications solution or just gamers?

As things have progressed with the PC, we have seen quite a few changes… and dead ends. ISA, 16 bit ISA, Proprietary 32 bit ISA, Vesa-Local Bus, Microchannel, PCI, AGP, PCI-x and now PCI-Express. Many of the aforementioned port types are obsolete after years of service. Others never caught on at all to any big degree. But technology moves forward. The original PCI Bus has been one of the long lived standards in PC architecture, having replaced ISA and having been around for around ten years at this point. It was followed by the AGP port which burst onto the video card scene in the summer of 1997, bringing with it bandwidth for video applications only enjoyed by high priced RISC based UNIX systems to that point. Now, enter PCI-Express Video; will it be right for your business applications and professional workstations? Hopefully, this article will answer that question and a few more for you.

Why did AGP Become The Video Standard?
Speed, plan and simple; speed is the main reason that AGP video cards became the standard. AGP had increased bus speed / bandwidth as well as its point to point architecture and that point to point protocol meant that AGP has its own path way to communicate with the processor as well as one to the memory, PCI based devices had to share the 133 MB/s worth of bandwidth allocated to it. While both AGP and PCI Bus are based on a 32 bit bus, AGP being clocked at 66 MHz versus 33 for PCI had double the bandwidth (266 MB/s) at its first introduction. With its ability to transfer data multiple times per clock cycle, AGP’s current implementation of 8x, has ~2100MB/s of bandwidth.

PCI Express
PCI Express (not to be confused with PCI-X) is the touted as the latest, upcoming replacement for both PCI and AGP. A couple of the main selling point of PCI Express are:

1. While the classic PCI Bus is based upon a parallel architecture, PCI Express is serial based, drastically reducing pin count.
2. It is a point to point protocol much like AGP. Devices do not share bandwidth

The design goals of PCI Express, per Intel and other developers, include a lower implementation cost as well, higher bandwidth per pin and scalable performance. The engineers behind the development of PCI Express did not want to be caught in the same situation as with the current PCI bus; while PCI bus was a robust architecture with over a decade of use (and continued use expected for at least a few more years); speeding up the PCI Bus is not really a feasible. It is kind of like adding a turbo and nitrous oxide to a Yugo; you could do it, but you would still have a Yugo!

Throughput comparisons
To really understand the way things work with the different bus types; you must see the bandwidth based on numbers of pins and the megabytes per second that can be transferred. The chart included here from Intel provides is with such a picture. The chart shows the relative complexity of PCI, PCI-X and AGP in comparison to PCI Express (also called 3GIO, 3rd Generation I/O). The strong point for PCI-Express in the future is that it calls for 2.5 Gb/s per direction which translates into roughly 250 MB/s per direction, roughly double the bandwidth of the current PCI bus. This transfer bandwidth is available to every device with PCI Express. The second part of the equation for PCI-Express is that for devices and slots that require high bandwidth, extra lanes can be added; x2, x4, x8, x12, x16 and x32 lanes are all possible with x16 making a debut as the next graphical bus interface. It looks good on paper, but as with so many other things that look good on paper, you need to see it in action to see if the bandwidth will really deliver the increased performance you seek.

Transitioning from AGP PCI Express
Most of the information I have read on PCI Express and transitioning to it includes a word that we do not like to see when we are talking about professional workstations; Gamers. They usually include a statement like ‘… the bad news for gamers is that it looks like on PCI Express motherboards, there will not be an AGP slot’ but this is also bad news and reason to be wary for business too. Any analysis that talks about gamers make me a bit nervous as the needs of a gamer and those of a professional working in a CAD/CAM or professional workstation environment are vastly different (come on, show of hands, anyone had a problem with a CAD application because they were using a card designed for video games?). According to industry buzz, no chipset manufacturer has had luck in implementing both yet. That means that if you have AGP based video cards, you will need to toss it out with the PC when you buy one with a PCI-Express based motherboard. Many manufacturers are very close to releasing PCI Express based products across their product line, but many do not exist and still more indicate that it will be some time until there are versions of PCI-Express video cards with drivers certified for high end CAD/CAM applications. Also of note is that many of those PCI-Express motherboards only have one PCI-Express slot, so once you install a video card, the need for speed may result in using something other than PCI-Express for your other peripherals. And that will result in the implementation and integration of more devices as peripheral controllers on the motherboard along with the current implementation and integration of SATA, IDE and Gigabyte LAN on the motherboard.

Immediate Benefits to the End User?
Immediate benefits, in this case, is marketing pablum trying to push this new technology. According to the industry, the main benefit at this point is that an investment in a PCI Express video card guarantees that it will work in future motherboards whereas AGP will have a limited life. The problem with that is that the same promises were made with VLB (Vesa-Local-Bus) Video cards. That choice had a practical life of less than a year. One area that should see the benefit of PCI-Express video speed is editing HD Video. Using programs like Adobe Premiere, the hardware always seems pushed to the limit when the end user tries to navigate through a large file. Having the ability to manipulate video directly from the video card should help a lot in those applications. While PCI Express may well be an important step in the evolving architecture of the PC’s communication bus, the immediate benefactors will be manufacturers and not the end user as PCI Express is supposed to be cheaper to implement than the traditional PCI Bus and the AGP slot. Consumers will find themselves between a rock and a hard place when PC’s with PCI Express start shipping. The biggest problem is, unless chipset vendors find a way to incorporate PCI-Express and AGP together, something they have been unable to so far, current AGP cards will not work. That will result in potentially costly upgrades. The next six months will tell. If vendors phase out AGP slots, then we will all know.


How can I get more information on this subject?
You can get more information about this subject? Well if you have support with us, ask us. Often times we will have additional suggestions you should think about in the long term when dealing with emerging technologies. If you have questions or comments about this article, contact me (JohnBoline@hagerman.com).
 

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