Skip to main content

Dual Graphics Platforms, Part II

The Battle Has Reached The South Bridge

While the chipset north bridge usually only hosts the PCI Express logic for attaching a graphics card (or two) to the system, the south bridge consists of all the interface logic and integrated devices. There are certain differences between the network interfaces and audio solutions that the chip manufacturers integrate, but the most important differentiator is certainly the storage subsystem.

Most chipsets offer four Serial ATA ports these days, mostly running at Serial ATA II or 2.5 specifications, while some are still at Serial ATA 1.0. While there is a bandwidth difference between SATA 1 and SATA 2.5 (150 vs. 300 MB/s max), the more interesting difference is RAID support.

When Intel introduced the 865 and 875 chipsets - codenamed Canterwood and Springdale - RAID support was added to the ICH5 south bridge, allowing the operation of two Serial ATA hard drives either in striping mode (RAID 0) or in secure RAID 1 mode. All that users required were Intel's Application Accelerator RAID drivers.

The 915/925 chipsets (Alderwood/Grantsdale) introduced a new south bridge called ICH6R, upgrading from two to four Serial ATA ports. In addition, a feature called Matrix RAID finally allowed the deployment of two different RAID arrays over one common set of hard drives.

Finally, the 945/955/975 chipset family upgraded the south bridge to ICH7R, and included RAID5 support. This mode requires at least three hard disks, and distributes parity data to all array members in order to prevent a total data loss in case any one drive should fail.

With more and more dual core processors becoming affordable, the performance penalty that RAID 5 entails can easily be tolerated. We decided to have a look at the storage subsystems' performance now.

South Bridge RAID Mode Overview

RAID ModeATI SB450nForce4 SLI X16ULi 1573ULi 1575VIA VT8251
RAID 0, two drivesxxXxX
RAID 1, two drivesxxXxX
RAID 0, four drives-x-xx
RAID 0+1, four drives-xXxx
RAID 5, three+ drives-x--x