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AMD's Spider Platform

Two Out of Three Ain't Bad

by Josh Walrath

790FX

            This is the glue that hangs all the pieces together.  The AMD 790FX is the first major chipset introduction for the AMD platform since the 690G back in February, and the nForce 500 series chipsets in the Summer of 2006.  Needless to say, the AMD motherboard market has been pretty stagnant as of late.  With the introduction of the new 700 series of chipsets, AMD is hoping to revitalize their motherboard market with an influx of new, exciting, and cutting edge motherboards.

            The 700 series chipsets will bring a handful of necessary new features to the game, but nothing that appears to be revolutionary.  The biggest feature is the support of PCI-E 2.0.  The new 2.0 spec brings double the bandwidth as the older PCI-E 1.x specification.  2.0 is also backwards compatible with 1.x devices, so older graphics cards/nics/RAID controllers that ran at PCI-E 1.x speeds will run perfectly fine on 2.0 boards.  The PCI-E 2.0 specification also allows for another 75 extra watts to be pumped through the 16X PEG slot, but that is merely an option rather than a compulsory requirement.  Most motherboards that we will see running PCI-E 2.0 will still continue to deliver the 75 watts of power that were found in 1.x slots.  Some workstation boards may in fact utilize the full 150 watts available via the 2.0 specification, but that will likely be the extent of it.

The MSI K9A2 looks to be the most mature board on the market so far, but further testing will reveal if that is a fact or merely wishful thinking.

            The new 700 chipsets will be fabricated on 65 nm, which will have positive results in terms of both die sizes and power draw.  AMD should be able to fit in a lot of these new chips onto one wafer, and that will keep the cost down overall for the motherboard manufacturers.  AMD is claiming that the new 790FX northbridge draws around 10 watts of power.  Unfortunately, in the one motherboard I have tested, it certainly seems to draw a lot more than that (namely the Gigabyte MA790FX-DQ6).

            The current 790FX chip features 42 PCI-E 2.0 lanes which can be flexibly allocated.  In regular CrossFire use, it will split up between 2 x 16X PEG slots, with 6 individual PCI-E lanes addressing integrated chips like network controllers, or routed to 1X through 4X slots for add-in cards.  In CrossFire X (the ability to use more than two cards in CrossFire) the boards can be configured up to 4 x 8X PEG slots.

The chipset communicates with the CPU via a HT 3.0 compliant connection.  This is still a 16 bit wide data path, but it communicates at 2GHz effective rather than the older 1 GHz speed.  HT 3.0 is also very flexible in its implementation, and can shut down lanes in order to maximize power usage.  AMD has claimed that it can in fact shut down the entire connection in sleep states without causing issues with the OS.

The 790FX uses the remaining 4 PCI-E lanes to communicate with the southbridge, in this case the older SB600 chip.  AMD is expecting to release the updated SB700 chipset early next year, and that adds another 2 USB ports as well as 2 more SATA ports.  AMD has done a lot of reworking internally to increase performance, as the SB600 was not necessarily known as a barn burner when it comes to I/O operations.  AMD is also adding hardware support for hybrid drives as well as other flash based memory technologies that are aimed at improving overall OS performance.  It is not a major upgrade, as it does not integrate anything like a networking accelerator (such as the nForce series have had for ages).  But when you consider that the northbridge has the extra 6 PCI-E lanes to throw at other peripherals, the outlook is not all that grim.

The 790X is essentially the same chip, but without the ability to handle CrossFire X.  The two x16 connections cannot be reconfigured to four x8 connections.  Other than that, the two chips are identical in their performance, power draw, and available lanes.

The 770 will be the budget/enthusiast model with only one 16X PEG connection.  Logically we can assume that the chip only features 26 PCI-E 2.0 lanes for distribution around the motherboard.  It also features the same HT 3.0 connection to the CPU.

Gigabyte showed off its MA790FX boards, plus their HD 3850 whose PCB was designed in-house and features a Zalman cooler.

The final member of the family is the RS780 chip, which is the next generation of integrated graphics parts from AMD.  This DX 10.1 compliant chip is due in Q1 of 2008, and all indications are pointing to it being a very impressive part (for integrated graphics that is).  I have heard rumors that it offers performance around that of the $70 to $80 range of standalone graphics cards in current 3D applications.  So expect around HD 2400 or GeForce 8400/8500 performance from this integrated part.  AMD certainly hopes this product will continue to build upon the success in the integrated world that the current 690G has already found.

The 700 series platform is certainly very exciting for AMD, and it has gotten the motherboard manufacturers interested in putting more effort into AMD based products.  The longevity of these chips is probably not in question, as they are all fabbed on a 65 nm process.  All other current chipsets use 80 nm to 130 nm processes, depending on the model.  The chips also seem feature complete, and apparently are some of the best examples of PCI-E 2.0 supporting technology to date (Intel’s X38 is the only other chipset featuring PCI-E 2.0 connectivity).

Next:  The RV670

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