14 DAY TRIAL // Since AMD's new SB750 was announced, various rumors concerning the performance enhancements of the South Bridge have emerged, especially regarding its capacities of improving communication with Phenom processors, allowing users to get it to higher overclocking levels. It seems that some of these rumors are true after all; at least, this is what has been revealed after the testing of the new SB750.
The I/O operations fall under the responsibility of the South Bridge. It runs the audio codecs, networking interfaces and virtually all other components. The North Bridge communicates directly with the CPU, connecting it to much higher speed components of the system, such as graphics cards or memory. This means that the typical overclocking performance is assumed to be negotiated with the NB, not the SB.
The SB750 seems to be an upgrade of the old SB700, yet it brigs many improvements over the SB600 used on today's 790FX boards. The new South Bridge includes six SATA 3.0Gb/s ports, allowing for two of them to be reserved to eSATA connectivity. The RAID 0, 1, or 10 drive configurations are available, along with a new brought RAID 5. AMD hasn't added a native network interface to it yet. AMD included an external PHY and MAC for network operations
The USB 2.0 performance is increased significantly with the SB750. There are 12 USB 2.0 capable ports and 2 specific 1.1 ports featured by the new dual-channel controller. The USB 2.0 performance resembles the one featured by the Intel and NVIDIA similar solutions.
There is also a single PATA channel which provides native IDE support for up to two drives. PIO, multi-word DMA, and Ultra DMA 33/66/100/133 are supported by the channel. There are five PCI lanes included, though they might not come with the boards from every manufacturer. Also, the Advanced Clock Calibration interface has replaced the HyperFlash support from the SB700.
As the SB700, the SB750 comes with a High Definition Audio controller, allowing for up to 16 channels of audio output per stream. The controller features support for up to four codecs with sample rates reaching 192kHz at up to 32-bits per sample.
A 6-pin interface to the AM2+ socket on the motherboard has been included in the SB750, and the Phenom CPU also features pins that allow it to directly connect to the SB750. The overclocking capabilities of the chip can also be increased through the SB750 combination with updated BIOS, which allows the overriding of some of the CPU's internal settings.
According to AMD, the settings tweak doesn't impact performance and it does not affect the thermals or voltages either, but it allows the Phenom to clock higher when in overclocking mode. Advanced Clock Calibration (ACC) value is the name AMD gave to the BIOS feature of exposing the parameter changed.
Only the Phenom processors allow for the SB750/ACC trick to be done, especially the Black Editions CPUs. AMD did not say anything about getting it to the K8 processors, so it remains only a Phenom feature for the time being. Since the processor has a few clock speed problems, AMD is focused on resolving them this way, and not as a short term solution, as the upcoming 45nm based Phenom parts are also announced to come with similar tweaks.
Tests conducted by the guys form AnandTech showed that overclocking works really well on the 32-bit versions of Windows XP and Vista, and less impressively on the 64-bit ones. Also, differences are spotted depending on motherboard, processor, BIOS settings and whether ACC was enabled or not. The bottom line is that Advanced Clock Calibration works, and that the SB750 is able to bring Phenom to higher clock speeds.