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The AMD 785G chipset that lies at the heart of the Asus M4A785TD-V EVO is an update to the AMD 780G that launched early in 2008. 780G was, to use an awful expression, a game changer. The HD 3200 graphics in 780G were head and shoulders above the competition in the integrated graphics market as they used 40 Unified Shaders with DirectX 10 and a superb HD movie decoder called UVD 1.0 along with proper digital video outputs. It really was an ideal platform for a media centre PC or as a simple low cost home PC that could compete on price and performance with the all conquering Intel Core 2 platofrom.
The HD 3200 graphics core was updated when AMD came up with the 790GX chipset however the only difference between HD 3200 and HD 3300 is an increase in clock speed from 500MHz to 700MHz. We have reviewed a number of 790GX motherboards such as the MSI 790GX-G65, which we loved to bits but the increase in graphics speed was pretty much the least interesting aspect of the motherboard. 790GX supports Socket AM3 Phenom II processors with DDR3 memory and is allied with a later Southbridge than the SB700 you'll find in 780G. The AMD SB710 Southbridge supports all the usual features such as SATA II, Gigabit Ethernet and HD Audio but it also packs in ACC (Advanced Clock Calibration) which greatly assists overclocking and which also allows you to unlock the extra core in Phenom II X3 processors. Further to this, the SB750 Southbridge enhances the SATA II RAID 0, 1 and 10 options in SB710 and adds RAID 5.
By contrast the 785G is a relatively minor update of 780G. The graphics core has been renamed as HD 4200 but it looks very similar to HD 3200 as it still has 40 Unified Shaders and is built on a 55nm process. DirectX support has been raised from 10.0 to 10.1 and HDMI support from 1.2 to 1.3. The movie decoder has been upgraded from UVD 1.0 to UVD 2.0 which appears to be a matter of adding a second decoder to handle multiple video streams. Realistically that will help picture-in-picture but it is hard to see that this will make a massive difference to many AMD customers. AMD tells us that 780G uses 205 million transistors while 785G uses ‘slightly more than 205 million transistors' so it is clear that the changes are not great.
The real mystery to us is that AMD bothered to update 780G when it could have been happily left to support legacy AM2/AM2+ CPUs while the obvious candidate for the update is 790GX. 795GX sounds like a suitably snappy name to us and we predict this will come complete with a 700MHz core speed.
So here we are with the Asus M4A785TD-V EVO and we're faced with a world of confusion. For starters there are the dual graphics PCI Express slots except they're not, not really. 780G/785G supports 22 lanes of PCI Express for expansion cards with 16 lanes reserved for the graphics slot so the second long PCI Express slot you see in the pictures only gets four lanes. Quite simply, there is no prospect of CrossFireX on offer with 785G.
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