AMD’s Peace Offering: SB750
790GX offers six additional lanes of PCI Express 2.0 connectivity that can be used by motherboard partners to integrate peripherals or enable expansion slots. AMD does not offer its own Gigabit Ethernet solution like Nvidia does, so there’s one PCIe link that’ll almost certainly be populated on 790GX-based boards.
The chip’s remaining four lanes of PCIe 2.0 constitute the connection between northbridge and southbridge. AMD brands the interface A-Link Xpress II and, if it were PCIe 2.0 on both ends, it’d deliver 4 GB/s of bi-directional throughput. Unfortunately, SB750 employs PCI Express 1.1, like its predecessor, capping bandwidth at 2 GB/s instead.
Making the Most
Once you make your way past the pedestrian chip-to-chip interconnect, you’ll find that there’s a lot more to like about SB750. On the superficial surface, USB 2.0 support remains pegged at 12 ports (with two 1.1 ports thrown in as well), HD Audio persists, a single parallel ATA channel accommodates two IDE devices, and six SATA 3 Gb/s port accommodate plenty of storage.
But whereas SB700 was limited to RAID 0, 1, and 10 arrays across its six ports, SB750 adds RAID 5 functionality to its list of accolades. That particular development is important because Nvidia and Intel already offer RAID 5, an increasingly popular mode for bolstering data security. AMD doesn’t say so in any of its supporting documentation, but we know from talking to company insiders that a particular effort went into improving the southbridge’s I/O performance, including its USB 2.0 and SATA components.
More important than RAID 5, expansive USB connectivity, or missing Gigabit Ethernet is a feature that AMD calls Advanced Clock Calibration, or ACC. There’s an aura of mystery shrouding what AAC actually does, which makes us nervous because vendors aren’t usually vague about the details of such potentially game-changing technologies unless there’s a good (bad) reason. What we do know about ACC is that it’s a direct, low-level link between the southbridge and CPU that AMD says “functions to unlock a number of tumblers on the processor previously not accessible.” Beyond that, with the proper cooling configuration, AMD claims simply enabling ACC is enough to boost overclocking headroom by between 100 and 400 MHz.
The feature comes most highly recommended for owners of Black Edition CPUs — the ones who’ve likely hit a wall with simple multiplier and voltage increases. But it will also work with any Phenom processor you drop into the 790GX platform. Given AMD’s reluctance to sing the specifics of ACC, we’ll have to let testing do the talking on this one.
The good news for true enthusiasts is that you won’t need to buy a 790GX with integrated graphics in order to reap the benefits of AMD’s SB750 southbridge. Fairly quickly we’ll start seeing 790FX-based motherboards retrofitted with the new component, bringing improved storage and overclocking to what we’d consider the true power user platform in AMD’s portfolio. The 790GX will be rightly confined to the folks able to use its integrated graphics core in a Hybrid CrossFire arrangement. In more rare cases, it may be tapped for its CrossFireX capabilities, though we’d just as soon go for one of the less expensive 790FX platforms sporting SB750. Originally we had hoped that the 790X platform would also receive some SB750 love. It’d seem to make sense as an alternative for budget-oriented gamers looking for an affordable CrossFireX setup without the need for integrated graphics. AMD doesn’t anticipate any of its partners taking that route, though.