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New Chipsets, New Features

The 925 and 915 chipset families feature support for many new technologies, including:

  • PCI-Express

  • GMA 900 integrated graphics*

  • DDR2 memory

  • High-Definition Audio

  • Matrix Storage Technology*

  • Second-generation Serial ATA (AHCI) support*

  • Wireless Connect Technology*

*Support for this feature varies by chipset

These new features are designed to make systems based on these chipsets:

  • Perform faster

  • Provide a better mix of data safety and system performance

  • Enjoy easier integration into Wi-Fi wireless networks at home and work

Let's take a closer look at each of these new technologies.


The most significant change in the new chipsets is the introduction of PCI-Express support. PCI-Express provides high-speed bi-directional connections between add-on cards and the chipset. Each connection is known as a lane: each lane runs at 100MBps in each direction, providing 200MBps overall throughput per lane. There are two different types of PCI-Express slots supported by the 915/925 chipsets:

  • PCI-Express x16 has 16 lanes, providing performance of 1,600MBps in each direction (3.2GBps overall throughput). This slot is used for high-speed video by all 915/925 chipsets except the forthcoming low-end 915GV. PCI-Express x16 connects to the Memory Controller Hub or Graphics Memory Controller Hub (North Bridge replacement) chip.

  • PCI-Express x1 has one lane, providing performance of 100MBps in each direction (200MBps overall throughput, compared to 133MBps for PCI). All 915 and 925 chipsets provide four PCI-Express x1 slots which connect to the ICH6-series I/O Controller Hub (South Bridge replacement) chip.

Eventually, PCI-Express x1 will replace PCI, but the 915 and 925 chipsets also support six PCI version 2.3 bus-master expansion slots. However, PCI-Express x16 is the only high-speed video slot supported by the 915 and 925 chipsets. These chipsets do not support AGP slots.

Intel Graphics Media Accelerator 900

The 915G Express chipset offers two options for graphics: the PCI-Express x16 expansion slot or a new generation of Intel integrated graphics, the GMA 900. The GMA 900 provides support for DirectX 9 (pixel shaders in hardware, vertex shaders in software), and independent dual displays including TV-out and DVI-out when a low-cost ADD2 card is plugged into the PCI-Express x16 slot (see http://english.aopen.com.tw/products/mb/Padd.htm for an example).

The GMA 900 uses 32MB of system memory for video at all times, but uses additional amounts temporarily allocated to it, depending upon the requirements of the software in use. The maximum amount of RAM it can use is 224MB. GMA 900 supports high resolutions and refresh rates, and is optimized to support 16:9 ratio widescreen LCD displays and HDTV at 720p and 1080i resolutions, making it a good solution for watching widescreen DVDs on your PC or on a big-screen TV connected to your PC.

Although serious game players will continue to prefer a discrete PCI-Express x16 solution, the GMA 900 will provide casual gamers and home computer users with a much more satisfactory experience than with previous Intel integrated chipsets. The forthcoming 915GV chipset will also include GMA 900, but will not provide support for a PCI-Express x16 slot.

DDR2 Memory Support

DDR2 memory differs in several ways from mainstream DDR memory:

  • DDR2 runs at faster speeds (533MHz now, faster speeds coming later)

  • DDR2 uses a lower voltage (1.8v versus 2.5v for DDR)

  • DDR2's internal design improves reliability, power usage, and memory access performance

The current 915 and 925 chipsets support 400MHz and 533MHz DDR2 memory. 915 chipsets can also use existing DDR memory. DDR2 memory uses a two-part 240-pin socket, compared to the two-part 184-pin socket used by DDR memory.

The ICH6 Family

The innovations in the 915 and 925 chipset families aren't limited to the MCH or GMCH (North Bridge) chip. These chipsets are the first to use Intel's new ICH6 family of I/O Controller Hub (South Bridge replacement) chips. Although the ICH5 family of chips included two versions (ICH5 and ICH5R with Serial ATA RAID support), the ICH6 family includes four versions:

  • ICH6 (basic features)

  • ICH6R (includes second-generation SATA RAID)

  • ICH6W (includes wireless network support)

  • ICH6WR (includes second-generation SATA RAID and wireless network support)

The following sections discuss the major features of these chipsets in detail.

High-Definition Audio

The 915 and 925 chipset families are the first to support Intel's High-Definition Audio (HDA) technology. Code-named Azalia, HDA surpasses the previous AC '97 2.3 standard in several ways:

  • Number of Channels. HDA supports eight-channel (7.1) audio, compared to AC '97 2.3 six-channel (5.1) audio support

  • Sound quality. HDA supports 192 KHz/32-bit audio sampling, compared to AC '97 2.3's 48KHz/20-bit audio sampling.

  • Dolby Digital audio support. HDA supports Dolby Digital audio standards through the latest Dolby Pro Logic IIx, which remixes stereo audio to support 7.1 surround sound speaker setups. AC '97-based Dolby Digital audio support is limited to 5.1 (six-channel) solutions at best.

Other advanced features of HDA include:

  • Dedicated system bandwidth to help eliminate glitches or pops common with older integrated audio standards.

  • Automatic speaker/microphone jack device detection and remapping. If you plug a microphone into a speaker jack, the system remaps the audio jacks rather than causing the audio subsystem to fail.

  • A unified driver and codec model known as Unified Audio Architecture.

  • Support for multiple audio streams to different playback locations (such as voice chatting while playing a 5.1-surround sound game)

Second-Generation Serial ATA Support

Although the ICH5 series of I/O controller hub chips used by the 845, 848, 865 and 875 chipsets were the first Intel chipsets to support Serial ATA, Serial ATA support was not the primary storage subsystem on the ICH5 series. With the ICH6 series, parallel ATA takes a distinctly secondary role to Serial ATA.

All four versions of the ICH6 I/O controller hub provide four Serial ATA ports (one drive per port), but only one ATA-100 port (two drives per port). However, the most significant improvement in Serial ATA support is included in the RAID versions of the ICH6 (ICH6R and ICH6WR):

  • Intel Matrix Storage Technology provides RAID 0 and RAID 1 support with only two drives

  • Advanced Host Controller interface supports Native Command Queuing and hot-swapping of Serial ATA drives

Intel Matrix Storage Technology

Ever since the first add-on cards and motherboards featuring ATA (and later Serial ATA) RAID were introduced, users of two-drive systems had to decide whether to opt for the increased performance of RAID 0 (striping) or the increased reliability of RAID 1 (mirroring) when configuring their drives. RAID 0+1 (speed plus reliability) support required four drives.

Intel Matrix Storage Technology (IMST) treats a two-drive SATA RAID array system as a combination of RAID 0 plus RAID 1, utilizing the speed advantages of RAID 0 for games and temporary file storage while providing the reliability of RAID 1 for business applications, data, and media files. IMST creates a striped array within the first half of the drives' disk space, and a mirrored array from the second half of the drives' disk space.

IMST also makes migrating from a single drive RAID-ready system to a two-drive RAID array simple: its configuration utility runs in the background, enabling you to work during the configuration process. A RAID-ready system uses ICH6R or ICH6RW, has the Intel Application Accelerator RAID option ROM on the motherboard, the Intel Application Accelerator driver, and the SATA RAID controller enabled in the BIOS.

As with the previous ICH5R chipsets, the RAID features in ICH6R and ICH6RW depend upon the use of the Intel Application Accelerator driver. Use version 4.0 or greater with the ICH6R or ICH6RW I/O controller hubs.

SATA II with Advanced Host Controller Interface

As I discuss in Chapter 7 of Upgrading and Repairing PCs, Fifteenth Anniversary Edition, it's no secret that the real-world performance of the first generation of SATA drives has been less than world-shaking. Although the SATA interface runs at 150MHz, making it faster than the 133MHz or 100MHz interfaces used by parallel ATA, the drive mechanisms and command sequences used by SATA and parallel ATA are comparable, leading to comparable real-world performance.

In addition to enabling IMST with the ICH6R and ICH6RW, the Intel Application Accelerator version 4.x also provides support for the Advanced Host Configuration Interface (AHCI). AHCI adds a number of features to the standard SATA interface, including:

  • native command queueing (NCQ)

  • hot-plugging of SATA drives (removal and insertion of drives while the power is on)

NCQ enables SATA drives to receive up to 32 commands in a single sequence and allows the drive to reorder the commands for best performance. Although most first-generation SATA drives do not support NCQ, some high-performance drives, such as the Maxtor MaxLine III and Seagate Barracuda 7200.7, include NCQ support. NCQ support enables 7,200 RPM NCQ-enabled SATA drives to outperform 10,000 RPM SATA drives without NCQ, according to Seagate tests. The combination of NCQ and IMST also boots performance, according to Intel tests.

Intel Wireless Connect Technology

The last major new feature in the ICH6 series is the wireless network support included in the ICH6W and ICH6RW versions. Intel Wireless Connect Technology (IWCT) goes far beyond a normal wireless network adapter. Its major features include:

  • Wi-Fi Certified 802.11b (11Mbps) and 802.11g (54Mbps) wireless network adapter

  • Setup wizard enables system to function as a network node on an existing wireless network or as a wireless access point for a new network

  • Supports bridging, routing, MAC address filtering, and network firewall for security and flexibility

  • Supports easy configuration of Microsoft Internet Connection Sharing

To enable IWCT, you must add a half-height PCI wireless network adapter known as the Intel PRO/Wireless 2225BG Network Connection. These cards will not be widely available until late in 2004.

DMI Hub Interface

With the new technologies included in both Memory Control Hub/Graphics Memory Control Hub and I/O Controller Hub components of the 915 and 925 chipsets, it's not surprising that a new hub interface was developed for these chipsets. The Direct Media Interface (DMI) hub architecture provides bandwidth of up to 2GBps concurrent data transfer between the chipset's components, compared to 266MBps with the earlier Intel Hub Architecture used by the 875 and 865 chipsets.

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