New chipsets underpin Intel's latest desktop PC platform

Intel's 925X (Alderwood) and 915P/G (Grantsdale) chipsets introduce new features that will allow CPU speed to develop without presenting I/O bottlenecks.

Although processors are the stars of the show in computer design, without their supporting circuitry they're only printed sand. And as processor design advances in speed, complexity and capability, the chipsets that surround them must change to support those capabilities with new and faster features. Intel's latest motherboard chipsets, previously codenamed Alderwood and Grantsdale, are aimed at high-performance motherboards and designed to work primarily with new and repackaged Pentium 4s ranging from the Pentium 4 520 at 2.8GHz to the P4 560 at 3.6GHz. All come with 1MB of Level 2 (L2) cache and an 800MHz frontside bus; there's also a repackaged Extreme Edition part. All are housed in a new Leadless Grid Array LGA775 package. This presents the chip's connections as a grid of conductors flush with the bottom of the case -- a technique previously used on the Pentium II core.

Intel's new LGA775 package presents the Pentium 4's connections as a grid of conductors flush with the bottom of the case.

925X and 915G/P chipsets
Alderwood and Grantsdale -- more properly, the Intel 925X and the 915G and P Express Chipsets -- introduce a set of upgrades and new features. Most are shared across the family: PCI Express, 800MHz frontside bus, dual-channel DDR2 533MHz memory support, integrated Gigabit Ethernet, four serial ATA and eight USB 2.0 ports, and Intel's High Definition Audio. The 925X supports ECC memory, unlike the 915 chips, while the latter work with a selection of older Pentiums and slower memory options. The 915G also includes integrated graphics, Intel's new Graphics Media Accelerator 900, and the chips include some high-level support for wireless access points (although the wireless network adapter itself isn't included).

The 925X chipset supports ECC memory, unlike the 915G (with integrated graphics) and 915P parts.
The chipsets support legacy PCI as well as four PCI Express (PCIe) x1 'lanes' (a lane is a single uncontended bidirectional 500MB/s bus running around 6.5 times faster than PCI). Intel has dropped AGP in favour of PCI Express x16. This combines 16 PCI Express lanes into one slot, together with 75 watts of available power. With 4GB/s available simultaneously in both directions, PCI Express x16 has around four times the total bandwidth of AGP 8X and is the performance graphics bus of choice for the next generation of PCs. Intel claims it can render four simultaneous 720-line high-definition TV images at 50 frames per second (fps). The 915G's integrated graphics are DirectX 9- and OpenGL 1.4-compatible, support QXGA (2,048-by-1,536 pixel) resolution at 85Hz and include hardware-accelerated pixel shading, shadow maps, volumetrix textures, depth bias and two-sided stencils. Intel says that the 915G delivers around 1.7 times better 3DMark 2001 performance than the graphics subsystem on the previous 865G chipset.

High Definition Audio
The High Definition Audio on the chips runs at a maximum of 192KHz 24-bit sample rate with eight channels, plus Dolby, DTS and DVD-Audio support. It also supports array microphones with up to 16 elements, a rather under-utilised technology that's useful for noise-cancelling voice recognition systems. This may be a feature of future operating systems. The final trick that the audio subsystem knows is 'jack retasking': it senses whether you've plugged a microphone, speaker or line-level audio connection into each jack and routes the audio signal appropriately. This could spell the end of the incomprehensible audio icon.

Intel's High Definition Audio supports array microphones with up to 16 elements -- useful for voice recognition systems.

Matrix Storage Technology
Intel is introducing its Matrix Storage Technology with this chipset -- strictly speaking, with the ICH6R southbridge chip. This has support for RAID 0/1 on a single two-drive array, as well as other configurations, including two RAID arrays on the four Serial ATA ports. It also includes native command queuing, where the hardware can re-order disk reads and writes to make optimal use of the head position over the disk surface, increasing performance by up to a claimed 74 percent.

DDR2 memory
Memory is faster and more flexible, thanks to DDR2 533MHz parts and a dual-channel memory path that can have the same or different amounts of RAM on each channel. The faster speed is unlikely to affect some classes of application much -- gamers can expect a couple of percent improvement over slower memory, if that -- but is useful for things like video editing and DVD playback.

With these chips, Intel is presenting its vision of how high-performance home and office desktop PCs will be configured over the next two to three years. Although none of the technologies introduced will result in major performance improvements by themselves, they will be able to track future processor enhancements without presenting I/O bottlenecks.

Intel has released several motherboards based on the 925 and 915 chipsets; the rest of the industry will follow in due course.
There'll be some lag while the rest of the industry introduces motherboards, graphics cards and other peripherals with drivers to take advantage of the new features, and it will take some time to be sure how the improvements translate into performance increases in real life, but the shape of this sector of the market has now been cast.


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