The 790FX is AMD’s top dog when it comes to the 7 series chipsets; its purpose is designed around high clock speeds, best in platform performance as well as supporting CrossfireX graphics configurations.
AMD’s 790FX chipset is based around a two chip solution. Thanks to AMD’s on CPU memory controller and its own integrated Northbridge, the external Northbridge is actually a Hyper transport to PCI Express controller hub. The 790FX is designed to be coupled with the Phenom processors so it comes with a single Hyper Transport 3.0 link between the Northbridge and the CPU.
The 790FX chipset has a total of 42 PCI Express lanes that support the new 2.0 specifications. 32 of the lanes are routed off for graphics setups, depending on the requirements; it can run two PCI Express x16 slots or routed across to four PCI Express x8 slots for CrossfireX setups. Six extra lanes are available for general expansion cards like SATA RAID chips, Gigabit LAN and TV tuners, again depending on what needs to be added on. The last four lanes are reserved for connecting the 790FX Northbridge to the Southbridge. Thanks to the PCI-E 2.0 specs this allows the 790FX to connect to a Southbridge at 4GB/s when connected to a PCI-E 2.0 compliant Southbridge.
The early 790FX chipsets that have hit the market are coupled with the older SB600 chipset that was built originally by ATI under the ATI branding; it only got a renaming to AMD SB600 after the ATI/AMD merger. The Northbridge to Southbridge connection is only at 2GB/s because it only supports PCI-E 1.1a specs. Its age begins to show as it only has four SATA ports compared to most that now run six. AMD has plans very soon to release the new SB700 chipset which will support six SATA ports, as well as additional RAID functions and a PCI-E 2.0 controller to allow 4GB/s connection between the North and South bridges.
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