Why do serial systems make such a difference? As an example take the Serial ATA controller cards and drives that recently emerged in the market. SATA was supposed to provide performance benefits that never really materialized but its interface is far superior.
When compared to the old parallel one, a serial ATA cable uses 8 wires while the older IDE cable required an 80 pin connection (40 for transmission and another 40 as ground). Parallel connections present problems when trying to upgrade their speed. Signals degrade and interference become troublesome (due to the 40 ground wires required in an IDE cable).
Serial connections reduce the complexity of the communications protocol thus reducing the pin count. Due to this the transmission speed may be significantly increased.
Through its transition from a parallel to a serial based architecture PCI Express aims to achieve a similar aim. PCI Express features a lower implementation cost, higher bandwidth per pin and scalable performance -all this, in an attempt to avoid the pitfalls of the current version.
The PCI Express is different in two ways- 2.5 Gb/s per direction translates into about 250 MB/s per direction, (twice the bandwidth of the current version) and this speed is available to each device. Secondly, the devices and slots that require high bandwidth can have extra lanes added to them (x2, x4, x8, x12, x16 and x32 lanes are possible).
Switching from AGP / PCI to PCI Express
If you are an avid gamer there is a downside to PCI Express. There will not be an AGP slot on PCI Express motherboards so this means that the new 9800XTs and 5950 Ultras will probably not work when after you upgrade your motherboard. It may be a good idea to avoid upgrading to a high end part, at this stage.
PCI Express is catching on rather slowly at present since the vast majority of current peripherals like SATA, IDE and Gigabyte LAN are integrated into the motherboard directly. On the i875, Intel has a Communications Streaming Architecture (CSA) bus dedicated for Gigabit LAN, in an attempt to avoid saturating the PCI bus. PCI Express will do away with the need for such additions.
Nforce 3 250 has Gigabit Ethernet built into its southbridge featuring a high speed connection to the processor but the PCI Express seems targeted towards the enterprise sector of the market (it makes good competition for PCI-X in terms of bandwidth and is likely to prove more cost effective.
RAID and SCSI cards will be appearing on the PCI Express bus. Look for SATA controller cards and 1394B cards on the PCI Express front.
HyperTransport Compatibility
Chipsets including the K8T800 and Nforce 3 rely on the HyperTransport 1 spec as a chip to chip interconnectivity protocol. The newer HyperTransport 2 specifications will provide mappings to PCI Express. HyperTransport and PCI Express promoters tell us that HyperTransport and PCI Express are not competing technologies (PCI Express features backplane connectivity protocols while HyperTransport is a chip to chip connectivity solution). HyperTransport is also and not a serial based connection.
