<%@LANGUAGE="JAVASCRIPT" CODEPAGE="1252"%> PCI Express notes


JUNE 2004
Compared to the progress made every year in other areas of computer technology such as processors and video cards, computer I/O system technology would seem to be standing still… in fact it is. Since the introduction of the original PCI bus back in the early 90's, very little has changed in the way that data is handled inside your computer. Hard drives, peripherals, LAN cards, sound cards, USB, and firewire all pass data through the same I/O system as your first 486 PC; the PCI bus running at 33mhz and shifting 133MB/s of data. As an example of recent technology, a Pentium 4 with DDR memory can shift 2.1GB/s across the memory bus. The 8x AGP bus can pass about 2.1GB/s of data a second too. These are technologies developed essentially to get around the limitations of the PCI. An ATA 133 hard drive on an Ultra/133 IDE controller card can theoretically overload the PCI bus all by itself, though only in brief bursts. The sustained transfer rate for current drives is too low to do this however. Now let's think about RAID, SCSI and now Gigabit Ethernet.... All of these data transfer technologies are trying to pump information through that slim little 133MB/s parallel PCI bus. This is the definition of a bottleneck. Now all things considered, it is probably a good thing that the PCI bus has remained essentially unchanged since its inception. For one thing, it works. It has provided a stable and flexible platform for hardware and software developers to build on for almost a decade. Anyone who remembers the days before Windows 95 and 'Plug and Play' devices will understand why computers have become so much more common since then. Now there are three other PCI specifications in existence, all designed to increase the amount of available bandwidth. These are 66MHz PCI, PCI-X at 64bit/133MHz, and the soon to be introduced PCI-X 2.0. The trouble is, while these technologies have, or soon will find a permanent home in the server market, the complexities and extra costs they introduce to motherboard manufacturing mean that they will be virtually unknown at the desktop level. PCI-X, for example, requires a controller for every slot and that is just too expensive. The solution to this is being backed by everyone's favorite processor manufacturer, Intel. Intel, in partnership with several other companies which include the likes of IBM, Dell, Compaq, HP and Microsoft have recently introduced what they hope will be the new standard for PC I/O in the years to come; PCI-Express (formerly 3GIO or 3rd Generation I/O) is the name which has been dubbed by PCI-SIG, the committee responsible for overseeing the PCI interface standard. Approved as a standard on April 17 2002, PCI-Express is intended to be an evolutionary upgrade to the existing PCI bus. It will maintain complete hardware and software compatibility with all recent PCI devices. In terms of form though, it is something completely new. What will PCI-Express mean to the PC? Like AMD's Hypertransport technology, PCI-Express is a 2-way, serial connection that carries data in packets, similar to the way it is transferred over Ethernet connections. The PCI-Express bus will no longer be a single parallel data bus through which all data is routed at a set rate. Rather, an assembly of serial, point-to-point wired, individually clocked ‘lanes' each consisting of two pairs of data lines will carry data upstream and downstream. As the technology goes to market, each of these lanes should be capable of a 2.5Gb/s data rate in each direction. The overall sustained transfer rate roughly equals 200MB/s. PCI-Express has been designed with future upgrades in mind, and should see increased results with later enhancements. Where the real performance benefit comes in is when more than one lane is added to a given point-to-point route. Lanes can be stacked together to increase the amount of bandwidth available to specific areas of the I/O system, such as the video card slot, for example. This technology will have a couple of immediate benefits. First of all, the amount of trace routes on any given motherboard will be considerably reduced by the adoption of point-to-point circuitry. Using 4 routes instead of 32 for a basic connection, you can see how motherboard manufacturers might well be enthusiastic about this technology, as this would significantly cut the costs of producing motherboards in the long term. Secondly, since each lane is exclusively used for communication between two points, there is no sharing of the available bandwidth. The objective then, is to create an I/O bus technology that will have the staying power that 32-bit PCI slots have enjoyed, a decade or more into the future. Upcoming technologies such as Intel's multi-Gigabit Ethernet 'Dual Northway" chipset, will inevitably require more bandwidth than PCI can currently offer, so its' phasing out in the server market seems inevitable. Development is already underway on a PCI-Express based replacement for the AGP8X video card interface. Currently dubbed the 'PCI-Express X16 slot,' video cards such as the upcoming nVidia NV36X, NV40 and ATI RV380 will use this interface when they hit markets in the first and second quarters of 2004. This implementation of the technology looks to have the potential to make current PCs obsolete even faster by completely supplanting AGP as the platform of choice for graphics card manufacturers. The 164-pin X16 slot is expected to provide a total usable bandwidth of around 4GB/s, double the 2.1GB/s bandwidth that the 8x AGP spec boasts. Otherwise, the X16 specification is pretty similar to AGP in terms of connector card size, though entirely non-compatible. One fairly exciting possibility for this upcoming technology is the potential for multiple graphics cards using the same high-speed connection. Currently it is possible to use more than one video card in a given system by combining an AGP card with a 32-bit PCI card. There is no apparent reason why the X16 spec could not be extended to include support for more than one slot, allowing multiple high-speed PCI-Express graphics cards... though at the moment, such a feature does not exist as far as we know. 75W Videocard Capabilities Currently PCI-Express X16 is being designed to provide up to 75W of power for video cards, as opposed to the current 25W/42W allowed by AGP8X. Most modern cards already consume more than this amount, as evidenced by the extra power connectors that appear on today's high-end video cards. Given that both ATI and Nvidia had a major part in the development of this new specification, and that major graphics companies from 3Dlabs to XGI have already announced support for the upcoming architecture, it looks like AGP's days are inevitably drawing to a close. To further depreciate the value of your very expensive AGP cards, PCI-Express X16 and 8x AGP slots cannot coexist on the same motherboard. That's okay, considering ATI and Nvidia will have essentially stopped producing high-end AGP graphics cards by the end of Q2:2004 anyway... Therefore when PCI-Express x16 motherboards do start hitting the market you will be pretty much forced to buy a totally new videocard. There have been rumors that SIS' R&D department in Taiwan has been quietly working on ways to get around this with their upcoming SIS756 chipset which reportedly supports both PCI-Express and AGP 8x standards, but as of this writing there have been no breakthroughs in the dual 8X AGP/PCI-Express x16 camp we know of. What makes up the PCI-Express bus? The PCI-Express bus is composed of multiple lanes of point-to-point wired copper interconnects serving all the components that used to just drop data into the older PCI bus. To make things even more flexible, a switch has been added to the architecture. Working in principle just like an Ethernet switch, this is intended to sit between the PCI-Express devices connected to the board and the rest of the I/O system. This will enable newer devices, for example PCI-Express connected on board Gigabit controllers or 10/100 gigabit network cards, to communicate with each other directly if necessary. By adding in this shortcut the data need not go through the chipset to reach an adjacent device. Compatibility between PCI 2.2 and PCI-Express As mentioned previously, the PCI-Express bus will be completely software compatible with PCI 2.2 compliant devices. Intel has already stated that all current operating systems will support PCI 2.2 compatible interface cards in the new PCI-Express system using the existing PCI drivers. This is an essential requirement if PCI-Express technology is to gain widespread acceptance. Forced obsolescence does not tend to go over well with computer users. The current specifics allow for an additional header placed at the end of a standard PCI slot to support lower bandwidth (1-2 lane) PCI-Express devices, somewhat similar to the extra connector used for 66mhz PCI devices. This is the most likely scenario for the first generation of PCI-Express motherboards based on upcoming chipsets such as Intel's Grantsdale-P and Alderwood. This feature combined with full software support will allow for a seamless integration with older PCI technology. Other chipset manufacturers are planning similar strategies, so expect to see PCI-Express slots popping up from the likes of SIS (SIS656, SIS662, SIS656FX, SIS756), VIA (PT890, PM890, K8T890), Nvidia (Crush 3GIO, Crush K8-04, Crush K8G3), ATI (RS480) and AMD in second half of 2004. The PCI 2.2 bus will be present to interface with PCI expansion cards and then will be linked via a PCI-Express connection to the main I/O. An altogether new connector has also been developed for high-bandwidth devices that need several PCI-Express lanes. While current use is still limited, a whole family of connectors for PCI-Express is in production. The PCI-Express specification calls for 1X (2.5Gb/s), 4x, 8x and 16x (4-5GB/s) connectors to begin with. The 1X connectors are intended to spearhead the adoption and integration of the new standard, while the introduction of the BTX motherboard form factor will cement the integration of PCI-Express into mainstream computing. The BTX form factor (announced at this years' IDF) is intended as the replacement for the current ATX motherboard standard, and included in its specifications are an X16 slot instead of an AGP connector for graphics, and two 1X PCI-Express connectors in place of several of the PCI slots. In the picture to the left, the PCI-Express slots are coloured blue. The BTX formfactor is beyond the scope of this article, so for more information about it look here. A PCI-Express 1X connector and bus would be ideal for gigabit Ethernet cards, as one example. In such an example, the Gigabit Ethernet wouldn't even have to be a physical card - it could just be an onboard GbE controller (BGA chip) soldered directly to the motherboard itself. PCI-Express X1, X4, X8, X16 1X should find a home in motherboards targeted to the desktop and PC enthusiast markets fairly early in the New Year. A projected model for a desktop system circa late 2004 might have PCI-Express 1X slots coexisting with PCI slots for expansion cards, and a single 16X slot for the graphics card, or have both the 1X slots as well as the X16 placed individually on the board, as per the BTX form-factor specifications. From speaking with several mainboard manufacturers; it would seem that most ATX motherboards in early 2004 will initially get equipped with two 1X PIC-Express connections; one a physical slot, and the other hooked directly to an onboard Gigabit Ethernet controller as described a moment ago. 1X 4X 8X PCI-Express connectors are similar in appearance and connection method that current 32-bit PCI slots. Designs for motherboards to be released in 2004 indicate that PCI-Express 1X slots will be about the size of current modem riser slots (about 1" long), while the X16 interface (164-pins) for graphics will be very similar in appearance to the standard AGP port. The flexibility to adapt to PCI-express devices of different bandwidths may be built into the midrange X4 and X8 slots. For the portable market, a new standard called the 'ExpressCard' has been created by the PCMCIA group in cooperation with the development of PCI-Express by the PCI-SIG group. Many of the companies involved in the work on PCI-Express are members of both trade associations, so it can be considered a joint effort. The ExpressCard is clearly meant to be a technology that bridges the gap between current notebook designs and future PCI-Express enabled ones. The interface and form-factor (similar in appearance to the current PC Card form factor for laptops) supports both USB2.0 and PCI-Express, allowing manufacturers to implement one or both without worrying about being ahead of or behind the times. Intel has used ExpressCard technology as an integral part of their 'Marble Falls' small form factor PC technology demonstration. ExpressCard slots will not be compatible with previous PC Card peripherals. Adding to the potential flexibility of the PCI-Express system, is the capability of external connections. The same 200MB/s point-to-point connections could be extended over cable outside the box to a distance of approximately 5 meters. Add this to the fact that designated PCI-Express connectors will be hot-pluggable, and you have the potential for some very interesting uses of the technology. External PCI Express devices road mapped Among other things, Intel has suggested a topology for the future that would separate the computing unit from the monitor, interface devices and external drives using PCI-Express cable connections as a go-between. A concept PC like that would enable complete modularity in servers and even desktop systems if manufacturers are willing to accept it. Of course, this is significantly beyond the current plans for PCI-Express, but if the technology is capable of supporting more user friendly expressions of computer form, they will probably be developed. PCI was developed in part to make computer configuration easier to handle, so there is no reason why PCI-Express should not take this to a new level. External video cards, anyone? Speaking from past experiences, I don't know how many times external components have been mentioned as a ‘wave of the future' type of thing; how about an entirely component based PC like a stereo system? It is unlikely that the makers of Firewire and USB 2.0 devices have much to worry about in the short term, despite the apparent ability of the PCI-Express technology to carry out their roles without even requiring a bridge to connect to the rest of the I/O system. USB and Firewire devices are already very common, and by the time external devices supporting the PCI-Express specification become available in a year or two, they should have become so prevalent in the market that manufacturers will have to continue support for them for the same reasons that PCI-Express was designed to coexist with PCI 2.2. Also, the ExpressCard format explicitly combines USB 2.0 and PCI-Express in a single slot for portable and small form factor devices. This is both an indication that PCI-Express is not necessarily intended to supplant USB anytime soon, and a concession to the continued usefulness of USB technology in the brave new world of sometime next year. It has been stated that PCI-Express is not intended to compete with AMD's Hypertransport technology, but rather coexist with it in order to move data more efficiently. Likewise, PCI-Express is intended to serve as the underlying data-transport technology for I/O methods like serial ATA and SCSI, not to replace them. PCI-Express is expected to replace AGP as the conduit between the graphics chipset and the processor and memory. As you can see, the modularity of the PCI Express system should enable it to carry out many different roles in the computer industry. As manufacturers will have the capability of deciding how much bandwidth to assign the needs of a specific market. Commenting on server technology is slightly beyond the scope of this article, but it is easy to see how PCI-Express technology could work well in this high-data area. The PCI-Express architecture is not intended to replace current CPU/memory bus technology, but rather to work with it by providing more available bandwidth and flexibility for the rest of the I/O system. While it was originally believed that the PCI-Express developers group might be looking at ways to standardize the CPU and memory buses within the system as well this is not part of the final approved specifications. Industry heavyweights 3Dlabs, ATI, Nvidia, and even AMD have already given PCI-Express their support, with AMD stating specifically that they see the PCI-Express technology working well with their Hypertransport technology. With endorsements like that it seems inevitable that the PCI-Express I/O system will be the basis for computers for many years to come.
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JUNE 2004

Compared to the progress made every year in other areas of computer technology such as processors and video cards, computer I/O system technology would seem to be standing still… in fact it is. Since the introduction of the original PCI bus back in the early 90's, very little has changed in the way that data is handled inside your computer.

Hard drives, peripherals, LAN cards, sound cards, USB, and firewire all pass data through the same I/O system as your first 486 PC; the PCI bus running at 33mhz and shifting 133MB/s of data. As an example of recent technology, a Pentium 4 with DDR memory can shift 2.1GB/s across the memory bus. The 8x AGP bus can pass about 2.1GB/s of data a second too. These are technologies developed essentially to get around the limitations of the PCI.

An ATA 133 hard drive on an Ultra/133 IDE controller card can theoretically overload the PCI bus all by itself, though only in brief bursts. The sustained transfer rate for current drives is too low to do this however. Now let's think about RAID, SCSI and now Gigabit Ethernet.... All of these data transfer technologies are trying to pump information through that slim little 133MB/s parallel PCI bus. This is the definition of a bottleneck.

Now all things considered, it is probably a good thing that the PCI bus has remained essentially unchanged since its inception. For one thing, it works.

It has provided a stable and flexible platform for hardware and software developers to build on for almost a decade. Anyone who remembers the days before Windows 95 and 'Plug and Play' devices will understand why computers have become so much more common since then.

Now there are three other PCI specifications in existence, all designed to increase the amount of available bandwidth. These are 66MHz PCI, PCI-X at 64bit/133MHz, and the soon to be introduced PCI-X 2.0.

The trouble is, while these technologies have, or soon will find a permanent home in the server market, the complexities and extra costs they introduce to motherboard manufacturing mean that they will be virtually unknown at the desktop level. PCI-X, for example, requires a controller for every slot and that is just too expensive. The solution to this is being backed by everyone's favorite processor manufacturer, Intel.

Intel, in partnership with several other companies which include the likes of IBM, Dell, Compaq, HP and Microsoft have recently introduced what they hope will be the new standard for PC I/O in the years to come; PCI-Express (formerly 3GIO or 3rd Generation I/O) is the name which has been dubbed by PCI-SIG, the committee responsible for overseeing the PCI interface standard.

Approved as a standard on April 17 2002, PCI-Express is intended to be an evolutionary upgrade to the existing PCI bus. It will maintain complete hardware and software compatibility with all recent PCI devices. In terms of form though, it is something completely new.

What will PCI-Express mean to the PC?

Like AMD's Hypertransport technology, PCI-Express is a 2-way, serial connection that carries data in packets, similar to the way it is transferred over Ethernet connections.

The PCI-Express bus will no longer be a single parallel data bus through which all data is routed at a set rate. Rather, an assembly of serial, point-to-point wired, individually clocked ‘lanes' each consisting of two pairs of data lines will carry data upstream and downstream. As the technology goes to market, each of these lanes should be capable of a 2.5Gb/s data rate in each direction. The overall sustained transfer rate roughly equals 200MB/s.

PCI-Express has been designed with future upgrades in mind, and should see increased results with later enhancements. Where the real performance benefit comes in is when more than one lane is added to a given point-to-point route. Lanes can be stacked together to increase the amount of bandwidth available to specific areas of the I/O system, such as the video card slot, for example.

This technology will have a couple of immediate benefits. First of all, the amount of trace routes on any given motherboard will be considerably reduced by the adoption of point-to-point circuitry.

Using 4 routes instead of 32 for a basic connection, you can see how motherboard manufacturers might well be enthusiastic about this technology, as this would significantly cut the costs of producing motherboards in the long term. Secondly, since each lane is exclusively used for communication between two points, there is no sharing of the available bandwidth.

The objective then, is to create an I/O bus technology that will have the staying power that 32-bit PCI slots have enjoyed, a decade or more into the future.

Upcoming technologies such as Intel's multi-Gigabit Ethernet 'Dual Northway" chipset, will inevitably require more bandwidth than PCI can currently offer, so its' phasing out in the server market seems inevitable.

Development is already underway on a PCI-Express based replacement for the AGP8X video card interface. Currently dubbed the 'PCI-Express X16 slot,' video cards such as the upcoming nVidia NV36X, NV40 and ATI RV380 will use this interface when they hit markets in the first and second quarters of 2004. This implementation of the technology looks to have the potential to make current PCs obsolete even faster by completely supplanting AGP as the platform of choice for graphics card manufacturers.

The 164-pin X16 slot is expected to provide a total usable bandwidth of around 4GB/s, double the 2.1GB/s bandwidth that the 8x AGP spec boasts. Otherwise, the X16 specification is pretty similar to AGP in terms of connector card size, though entirely non-compatible.

One fairly exciting possibility for this upcoming technology is the potential for multiple graphics cards using the same high-speed connection. Currently it is possible to use more than one video card in a given system by combining an AGP card with a 32-bit PCI card. There is no apparent reason why the X16 spec could not be extended to include support for more than one slot, allowing multiple high-speed PCI-Express graphics cards... though at the moment, such a feature does not exist as far as we know.

75W Videocard Capabilities

Currently PCI-Express X16 is being designed to provide up to 75W of power for video cards, as opposed to the current 25W/42W allowed by AGP8X. Most modern cards already consume more than this amount, as evidenced by the extra power connectors that appear on today's high-end video cards.

Given that both ATI and Nvidia had a major part in the development of this new specification, and that major graphics companies from 3Dlabs to XGI have already announced support for the upcoming architecture, it looks like AGP's days are inevitably drawing to a close. To further depreciate the value of your very expensive AGP cards, PCI-Express X16 and 8x AGP slots cannot coexist on the same motherboard. That's okay, considering ATI and Nvidia will have essentially stopped producing high-end AGP graphics cards by the end of Q2:2004 anyway...

Therefore when PCI-Express x16 motherboards do start hitting the market you will be pretty much forced to buy a totally new videocard. There have been rumors that SIS' R&D department in Taiwan has been quietly working on ways to get around this with their upcoming SIS756 chipset which reportedly supports both PCI-Express and AGP 8x standards, but as of this writing there have been no breakthroughs in the dual 8X AGP/PCI-Express x16 camp we know of.

What makes up the PCI-Express bus?

The PCI-Express bus is composed of multiple lanes of point-to-point wired copper interconnects serving all the components that used to just drop data into the older PCI bus. To make things even more flexible, a switch has been added to the architecture.

Working in principle just like an Ethernet switch, this is intended to sit between the PCI-Express devices connected to the board and the rest of the I/O system. This will enable newer devices, for example PCI-Express connected on board Gigabit controllers or 10/100 gigabit network cards, to communicate with each other directly if necessary. By adding in this shortcut the data need not go through the chipset to reach an adjacent device.

Compatibility between PCI 2.2 and PCI-Express

As mentioned previously, the PCI-Express bus will be completely software compatible with PCI 2.2 compliant devices. Intel has already stated that all current operating systems will support PCI 2.2 compatible interface cards in the new PCI-Express system using the existing PCI drivers.

This is an essential requirement if PCI-Express technology is to gain widespread acceptance. Forced obsolescence does not tend to go over well with computer users.

The current specifics allow for an additional header placed at the end of a standard PCI slot to support lower bandwidth (1-2 lane) PCI-Express devices, somewhat similar to the extra connector used for 66mhz PCI devices.

This is the most likely scenario for the first generation of PCI-Express motherboards based on upcoming chipsets such as Intel's Grantsdale-P and Alderwood. This feature combined with full software support will allow for a seamless integration with older PCI technology. Other chipset manufacturers are planning similar strategies, so expect to see PCI-Express slots popping up from the likes of SIS (SIS656, SIS662, SIS656FX, SIS756), VIA (PT890, PM890, K8T890), Nvidia (Crush 3GIO, Crush K8-04, Crush K8G3), ATI (RS480) and AMD in second half of 2004.

The PCI 2.2 bus will be present to interface with PCI expansion cards and then will be linked via a PCI-Express connection to the main I/O.

An altogether new connector has also been developed for high-bandwidth devices that need several PCI-Express lanes. While current use is still limited, a whole family of connectors for PCI-Express is in production. The PCI-Express specification calls for 1X (2.5Gb/s), 4x, 8x and 16x (4-5GB/s) connectors to begin with.

The 1X connectors are intended to spearhead the adoption and integration of the new standard, while the introduction of the BTX motherboard form factor will cement the integration of PCI-Express into mainstream computing.

The BTX form factor (announced at this years' IDF) is intended as the replacement for the current ATX motherboard standard, and included in its specifications are an X16 slot instead of an AGP connector for graphics, and two 1X PCI-Express connectors in place of several of the PCI slots.

In the picture to the left, the PCI-Express slots are coloured blue. The BTX formfactor is beyond the scope of this article, so for more information about it look here.

A PCI-Express 1X connector and bus would be ideal for gigabit Ethernet cards, as one example. In such an example, the Gigabit Ethernet wouldn't even have to be a physical card - it could just be an onboard GbE controller (BGA chip) soldered directly to the motherboard itself.

PCI-Express X1, X4, X8, X16

1X should find a home in motherboards targeted to the desktop and PC enthusiast markets fairly early in the New Year. A projected model for a desktop system circa late 2004 might have PCI-Express 1X slots coexisting with PCI slots for expansion cards, and a single 16X slot for the graphics card, or have both the 1X slots as well as the X16 placed individually on the board, as per the BTX form-factor specifications.

From speaking with several mainboard manufacturers; it would seem that most ATX motherboards in early 2004 will initially get equipped with two 1X PIC-Express connections; one a physical slot, and the other hooked directly to an onboard Gigabit Ethernet controller as described a moment ago.

1X 4X 8X

PCI-Express connectors are similar in appearance and connection method that current 32-bit PCI slots. Designs for motherboards to be released in 2004 indicate that PCI-Express 1X slots will be about the size of current modem riser slots (about 1" long), while the X16 interface (164-pins) for graphics will be very similar in appearance to the standard AGP port. The flexibility to adapt to PCI-express devices of different bandwidths may be built into the midrange X4 and X8 slots.

For the portable market, a new standard called the 'ExpressCard' has been created by the PCMCIA group in cooperation with the development of PCI-Express by the PCI-SIG group. Many of the companies involved in the work on PCI-Express are members of both trade associations, so it can be considered a joint effort.

The ExpressCard is clearly meant to be a technology that bridges the gap between current notebook designs and future PCI-Express enabled ones.

The interface and form-factor (similar in appearance to the current PC Card form factor for laptops) supports both USB2.0 and PCI-Express, allowing manufacturers to implement one or both without worrying about being ahead of or behind the times.

Intel has used ExpressCard technology as an integral part of their 'Marble Falls' small form factor PC technology demonstration. ExpressCard slots will not be compatible with previous PC Card peripherals.

Adding to the potential flexibility of the PCI-Express system, is the capability of external connections. The same 200MB/s point-to-point connections could be extended over cable outside the box to a distance of approximately 5 meters. Add this to the fact that designated PCI-Express connectors will be hot-pluggable, and you have the potential for some very interesting uses of the technology.

External PCI Express devices road mapped

Among other things, Intel has suggested a topology for the future that would separate the computing unit from the monitor, interface devices and external drives using PCI-Express cable connections as a go-between.

A concept PC like that would enable complete modularity in servers and even desktop systems if manufacturers are willing to accept it. Of course, this is significantly beyond the current plans for PCI-Express, but if the technology is capable of supporting more user friendly expressions of computer form, they will probably be developed.

PCI was developed in part to make computer configuration easier to handle, so there is no reason why PCI-Express should not take this to a new level. External video cards, anyone? Speaking from past experiences, I don't know how many times external components have been mentioned as a ‘wave of the future' type of thing; how about an entirely component based PC like a stereo system?

It is unlikely that the makers of Firewire and USB 2.0 devices have much to worry about in the short term, despite the apparent ability of the PCI-Express technology to carry out their roles without even requiring a bridge to connect to the rest of the I/O system. USB and Firewire devices are already very common, and by the time external devices supporting the PCI-Express specification become available in a year or two, they should have become so prevalent in the market that manufacturers will have to continue support for them for the same reasons that PCI-Express was designed to coexist with PCI 2.2.

Also, the ExpressCard format explicitly combines USB 2.0 and PCI-Express in a single slot for portable and small form factor devices. This is both an indication that PCI-Express is not necessarily intended to supplant USB anytime soon, and a concession to the continued usefulness of USB technology in the brave new world of sometime next year.

It has been stated that PCI-Express is not intended to compete with AMD's Hypertransport technology, but rather coexist with it in order to move data more efficiently.

Likewise, PCI-Express is intended to serve as the underlying data-transport technology for I/O methods like serial ATA and SCSI, not to replace them. PCI-Express is expected to replace AGP as the conduit between the graphics chipset and the processor and memory.

As you can see, the modularity of the PCI Express system should enable it to carry out many different roles in the computer industry. As manufacturers will have the capability of deciding how much bandwidth to assign the needs of a specific market. Commenting on server technology is slightly beyond the scope of this article, but it is easy to see how PCI-Express technology could work well in this high-data area.

The PCI-Express architecture is not intended to replace current CPU/memory bus technology, but rather to work with it by providing more available bandwidth and flexibility for the rest of the I/O system.

While it was originally believed that the PCI-Express developers group might be looking at ways to standardize the CPU and memory buses within the system as well this is not part of the final approved specifications.

Industry heavyweights 3Dlabs, ATI, Nvidia, and even AMD have already given PCI-Express their support, with AMD stating specifically that they see the PCI-Express technology working well with their Hypertransport technology. With endorsements like that it seems inevitable that the PCI-Express I/O system will be the basis for computers for many years to come.

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