ASUS Sabertooth 990FX AM3+ Motherboard Review

Author: MAC
Date: May 30, 2011
Product Name: ASUS 990FX Sabertooth
Warranty: 5 Years
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The 990FX Under the Microscope

AMD’s “new” range of 900-series motherboards spans the upper end of their market and will initially consist of the 990FX and 990X chipsets.

The “990FX” may indeed sound new but it is nothing more than an 890FX with updated microcode to support upcoming Zambezi processors while the 950 Southbridge is simply a rebranded SB850 chip. Is this a bad thing? Well, we don’t think so because the 890/850 combination used on previous boards proved to be forward thinking enough that many of its features (like SATA 6G and USB 3.0) are still in their infancy and have a long way to grow.

One of AMD’s most distinguishing features over the last few product generations has been their commitment to offering backwards compatibility for their motherboards and forwards compatibility on the processor end of things. Even though the 990FX series boards will feature support for upcoming AM3+ processors, the socket layout makes them compatible with all current AM3 processors as well. This will allow current and slightly older processors to be used on these boards. So while 990FX may not seem like an upgrade for 890FX users, it is a no-brainer purchase for people who want an AMD platform now but are worried about what’s coming down the pipeline.

While Intel has transferred most of their Southbridge functionality to their processor die, AMD has staunchly adhered to a two-part chipset configuration consisting of a Northbridge and a Southbridge. We have seen this layout persist through the 790FX days on to the 890FX and now once again on the 990FX. This may change in the future, for the time being all current AM3 processors and upcoming AM3+ products only feature on-chip DDR3 memory controllers while all the I/O and expansion slot functions are handled through the chipset. We also get native support for DDR3 1333Mhz memory while the processor and 990FX Northbridge communicate through a Hypertransport 3.1 link at 6.4 GT/s. Yes, that's an upgrade which will likely benefit processors.

The Northbridge of AMD’s two-chip solution acts as a controller hub for most of the board’s PCI-E 2.0 lanes and facilitates communication between the SB950 and the processor. The 32 dedicated graphics card lanes are split up into either two 16x slots or can be evenly dispersed for up to a quartet of 8x slots which gives the boards incredible flexibility for multi GPU setups.

After a long hiatus, SLI finally sees the light of day on an AMD chipset with support through NVIDIA’s driver stack. This is a huge step for both AMD and NVIDIA and it could open up some new markets for these motherboards.

Meanwhile, the remaining ten PCI-E 2.0 lanes are divided up into one grouping of four lanes while an additional six lanes 1x lanes can be dispersed as needed for integrated components like audio and networking controllers.

This layout tells us a thing or two about the Bulldozer-based Zambezi CPUs which are due out in the coming months. It seems like their baseline interface with supporting motherboards hasn’t changed much from the current generation of processors which means they’ll retain the on-die memory controller while supporting DDR3 speeds of 1333Mhz. This can be counted as a good thing for consumers and motherboard manufacturers alike since motherboards will likely stay relatively inexpensive compared to their Intel competitors.

Moving on down to the SB950, we see that AMD has once again foregone any updating as the layout is absolutely identical to that of the SB850. The chipset interconnect still uses a 2GB/s interface dubbed “Alink Express III” which essentially uses four PCI-E 2.0 lanes to speed up on-board communications.

Speaking of the Southbridge, we see that AMD has retained 6Gbps SATA support but still hasn’t progressed to native USB 3.0 support. Third party USB 3.0 controllers can be interfaced to the Southbridge or Northbridge chipsets using the 1x PCI-Express 2.0 lanes for a maximum theoretical throughput of 500MB/s.

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