Author: William Henning
Editor: Howard Ha
Publish Date: Friday, August 8th, 2008
Originally Published on Neoseeker (http://www.neoseeker.com)
Article Link: http://www.neoseeker.com/Articles/Hardware/Reviews/amd_790gx/
Copyright Neo Era Media, Inc. - please do not redistribute or use for commercial purposes.
It's time for another chipset launch - and this time we are writing about AMD's new 790GX integrated graphics chipset.
The 790GX is built upon the previously well received 780 chipset, and provides the following capabilities:
One of the most interesting features of the 790GX chipset is actually more of an SB750 southbridge feature - that is improved overclocking of Phenom processors with what AMD calls "Advanced Clock Calibration".
AMD really does not want to talk about how this works, and skirted around giving details during a web conference, however there are a couple of things we know:
From this, we can hypothesize that what may be going on is that AMD may be using some general purpose I/O pins on the SB750 to control the signal levels of some of the processor pins - in effect having the strapping of some option pins controlled by software instead of hardware manufacturers strapping control pins to either "high" or "low".
Effectively this could allow control of certain delays - say having to do with with rise/fall times on Hypertransport, or it could control voltages used for interfacing, or rise/fall times of internal signals.
Whatever it controls, AMD claims that it allows noticably better overclocking, and there are anecdotal reports that processors that would only overclock to 2.8 or 2.9GHz with a 780G chipset can clock to 3.2GHz with the 790GX - however I will reserve judgement until I can try this myself.
AMD also updated its "AMD Overdrive" overclocking utility - it looks much better now:
Probably the most significant performance advantage to some 790GX implementations is the side port memory.
The biggest performance limitation for integrated graphics chipsets is that they share the system memory - and in the case of AMD systems, the IGP has to make memory requests that go through the processor via the HyperTransport link to the chipset.
By allowing for higher HyperTransport speeds, the 790GX already has a big advantage for IGP graphics over previous AMD IGP solutions; however the addition of the "side port" memory provides it with an even bigger advantage - as it now has its own private frame buffer memory that it can access without having to go to the main memory through the processor. It is basically the same as having a frame buffer on a plug in PCIe video card!
Talking about PCIe, the support for PCIe 2.0 means that for GPU's that support it, either of the PCIe 8x GPU slots can provide the same ammount of bandwidth that was previously available from a PCIe 1.0 16x slot - so CrossFire will definitely not be limited by PCIe bandwidth for the forseable future.
The 790GX provides two independent display controllers, both capable of driving displays over HDMI. Theoretically there is nothing to stop you from playing back two Blu-Ray movies at once, one on each display!
The 790GX IGP graphics are supposed to be up to 33% faster than the 780G's - the GPU clock was increased to 700MHz from 500MHz and the GPU can be overclocked to around 1000MHz. Hybrid CrossFire is up to 40% faster than on a 780G.
All of AMD's regular partners will be bringing out 790GX based boards; and Gigabyte sent us some information on their upcoming MA790GP-DS4H board:
We will be taking a close look at a 790GX board in the near future - I am quite intrigued by the possibility of increased overclocking of Phenom CPU's, not to mention the possiblity of Hybrid Crossfire providing usable gaming with an inexpensive 3470 card added to the system - which would also allow supporting four monitors!
The 790GX looks very good on paper, now it needs a processor that can really take on Penryn, and later Nehalem. It will be very interesting to see how the upcoming 45nm Deneb shrink of Phenom will perform!
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