990FX & AM3+; More Lives Than Disco
990FX & AM3+; More Lives Than Disco
Welcome to the future....and the past. AMD has staunchly adhered to their AM3 platform for the last few CPU generations and not much has changed here. This time around, the AM3+ 900-series chipsets (970, 990X and 990FX) are being carried forward en masse and they all boast forwards compatibility with the new Vishera FX CPUs. Due to the architectural similarities between Zambezi and Vishera this shouldnít come as any surprise and users with an eye to upgrade from slightly older CPUs will count this as a blessing.
While the 900 chipsets were derived from previous 800-series designs, these older chipsets donít typically support the new AM3+ Vishera processors since there was a power spec revision right before 990FX was released. However, according to AMD, some motherboard vendors were able to include this updated design into their late 800-series products so there may be some older boards that actually do support Vishera. We suggest checking with your motherboard vendor prior to assuming compatibility with these new processors.
Since the market is going to be using this platform for the next year or so, letís go through a quick crash course on the 990FX and the features it brings to the table.
At its heart the 990FX is simply an 890FX with updated microcode and expanded power modes to support the latest Bulldozer-based processors (Zambezi and now Vishera) while the 950 Southbridge is simply a rebranded SB850 chip. Is this a bad thing? Well, we donít 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) are still very much legitimate today.
While Intel has transferred most of their Southbridge functionality to their processor die, AMDís AM3 chipset remains a two-part configuration consisting of a Northbridge and a Southbridge. We have seen this layout persist through the 790FX days on to the 890FX and the 990FX as well. This may change in the future but for the time being all current AM3+ products 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 to 1866MHz memory while the processor and 990FX Northbridge communicate through a Hypertransport 3.1 link at 6.4 GT/s.
The Northbridge of AMDís two-chip solution acts as a controller hub for most of the boardís PCI-E 2.0 lanes and facilitates communication between the SB950 and the processor. PCI-E 3.0 isnít supported but as we have seen in the past, the benefits the new protocol brings to the table are virtually nonexistent, even with todayís high-end dual GPU cards.
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. Naturally, SLI and Crossfire are fully supported.
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.
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 ďAlink Express IIIĒ which essentially uses four PCI-E 2.0 lanes to speed up on-board communications.
Speaking of the Southbridge, we see that AMD has native 6Gbps SATA support but integrated USB 3.0 support was never included on these chipsets or the processors themselves. 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.
So there you have it. What was old is new again and while motherboard vendors arenít too pleased about AMDís decision to keep 990FX around for yet another generation, end users will end up benefitting. These motherboards are typically quite affordable and anyone that already has one will only need a $195 processor to complete a Vishera-based system.
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