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Asus SK8N: Single-processor Opteron with nForce3 Pro 150
The first of the three workstation platforms we're comparing today is based on NVIDIA's nForce3 Pro 150 chipset. This Opteron core-logic chipset is a single-chip solution intended only for single-processor systems. Asus was first to market with the nForce3 Pro, and as far as I know, the SK8N motherboard is still the only nForce3 Pro mobo available.


Asus' SK8N has an unconventional but clean layout

Because we're dealing with an Opteron here, the core-logic chipset arrangement is a bit different from a traditional system. The dual-channel Opteron memory controller is integrated on the processor, so there's no conventional north bridge, and memory access doesn't happen over the front-side bus. What's more, NVIDIA has folded the remaining north bridge functions into a single chip along with the usual south bridge I/O capabilities. The Opteron processor communicates with the lone nForce3 Pro chip over a HyperTransport connection. HyperTransport provides the key plumbing for K8-based systems, offering a high-bandwidth transport over pairs of narrow, unidirectional links with high clock speeds. In the case of the nForce3 Pro 150, those links provide 3.6GB/s of peak bandwidth.

The nForce3 Pro supports most of the latest standards, including AGP 8X, ATA/133, and USB 2.0. This chipset doesn't have a native Serial ATA controller, but NVIDIA says one of the chipset's three ATA/133 channels can be overclocked and bridged to support two SATA devices (a master and a slave) at 150MB/s. Asus chose not to go that route, opting instead for a Promise RAID controller. Curiously, NVIDIA's datasheet also says the nForce3 Pro supports RAID levels 0, 1, and 0+1, but the SK8N manual mentions only RAID via the Promise controller.

The SK8N lacks some of the high-end features present in many workstation systems today, like 64-bit/66MHz PCI or PCI-X slots and AGP Pro. Also, surprisingly, there's no Gigabit Ethernet support, only a 10/100 Ethernet controller based on the Ethernet MAC in the nForce3 Pro. The SK8N isn't certified for NVIDIA's SoundStorm, either. Asus chose Realtek's low-cost ALC650 codec for the SK8N, and supplies Realtek audio drivers with the board.

Unlike most desktop systems, though, the memory controller in the Opteron chip requires registered DIMMs in order to operate properly. (We tried to get the system to boot with non-registered DIMMs, to no avail.) Registered memory relieves some of the electrical load on the memory controller, but it does so at the expense of one clock cycle of additional memory access latency. Given the proximity of Opteron's built-in memory controller, that's a fair trade-off. The K8 memory controller also supports ECC memory for improved data integrity, though it doesn't require ECC DIMMs.

All in all, the nForce3 Pro is a decidedly low-end workstation chipset, especially as implemented on the Asus SK8N. With the exception of its single-processor limitation, though, it fits in nicely with the other platforms we're looking at here. Expect the desktop versions of nForce3 for the upcoming Athlon 64 to look very similar to the nForce3 Pro.