AMD 790GX Chipset

AMD 790GX Chipset

If you've been on top of the PC scene for any length of time, you probably know that whether by choice or necessity, AMD has taken a different tact as of late. Whereas the company was all about bigger, faster, and better during the Athlon's heyday, AMD is now more about touting the performance per dollar and value of their products. While they may not have a CPU with the horsepower to compete in the benchmark war with Intel's $1000 behemoths, AMD's affordably priced Phenoms do offer good bang for the buck.

The value conscious mentality that has permeated AMD's recent graphics card and processor launches has also rung true in their motherboard chipset business as well. The 690G and 780G, for example, offered solid feature sets and excellent IGPs, at very affordable prices. And today, AMD continues their recent traditions with the introduction of the 790GX chipset.

The AMD 790GX is a tough product to categorize. It is targeted at value conscious gamers, enthusiasts, and multimedia buffs all at the same time. The block diagram above gives a high-level overview of the chipsets main features and illustrates how each component is connected in the architecture.

As you can see, the AMD 790GX Northbridge is connected to the AM2+ socket through a HyperTransport 3.0 link and it sports and integrated graphics core, along with a flexible PCI Express lane configuration. PATA, 6 SATA ports, HD audio, and 12 USB ports are supported by the SB750 Southbridge. Also, at the bottom of the diagram, a new feature you may not be familiar with, makes its debut--ACC, or Advanced Clock Calibration. More of ACC a bit later.

The AMD 790GX is manufactured at 55nm and features an Integrated Radeon HD 3300 Graphics Processor (IGP) that integrates a DirectX10 compliant Shader Model 4.0 graphics core, a Unified Video Decoder (UVD), two x8 PCI Express 2.0 links or 1 x16 link, HyperTransport 3.0, DVI / HDMI interface, and internal / external TMDS and DisplayPort capability in a single chip. The graphics core is actually identical to the one found in the 780G, but in the 790GX, it is clocked much higher (700MHz) for up to 33% better performance, PowerPlay features have been enahnced to support lower power states, and many boards featuring the 790GX will be equipped with dedicated sideport memory, for increased performance. Of course, the 790GX supports ATI Hybrid CrossFire technology as well, for increased performance or low-power operation.

The AMD SB750 Southbridge communicates with the Northbridge through the A-Link Express II interface. The AMD SB750 offers support for both SATA RAID and IDE drives and it is the key piece in the Advanced Clock Calibration puzzle. In total, the SB750 supports 6x SATA 3.0 Gb/s ports that can be setup in IDE, AHCI, JBOD, RAID 0, RAID 1, RAID 5 or RAID 10 modes, 12x USB 2.0 and 2x USB 1.1 ports, DASH 1.0, 6x PCI slots, HD Audio, IDE, and Serial and Parallel ports.

To evaluate the new AMD 790GX chipset, we got out hands on a retail ready motherboard from Gigabyte, the MA790GP-DS4H.

The Gigabyte MA790GP-DS4H exposed all of the features inherent to the 790GX and adds many more through the use of additional on-board controllers. As you can see, the board is passively cooled by an array of copper heatsinks linked together via a pair of copper heatpipes, and is this completely silent. During testing, we found the heatsinks to get just warm to the touch so heat should not be an issue here.The board is outfitted with three PCI Express x1 slots, two x16 PEG slot (with x8 electrical connections) and two standard PCI slots. All of its main connectors and headers are situated around the edges of the board, save for a band of four USB headers, located just behind the third x1 slot. The board’s headers are clearly marked, labeled, and color coded, which made working with the MA790GP-DS4H a breeze during setup. Overall we found the layout to be good.

In the MA790GP-DS4H’s external I/O port cluster, you’ll find PS/2 mouse and keyboard ports, VGA, DVI, and HDMI display outputs (any two can be used simultaneoudly with only the IGP), four USB ports, analog and digital HD audio outputs, a Gigabit LAN port, and finally a Firewire port. The board’s audio comes by way of a Realtek ALC889A 8-Channel HD codec, Firewire by way of a TI controller, and Gigabit LAN duties are handled by a Realtek RLT8111 chip.We should also note, that the MA790GP-DS4H's integrated Radeon HD 3300 IGP is backed by 128MB of 1333MHz dedicated frame buffer memory. Having dedicated frame buffer memory (dubbed sideport memory), makes the IGP essentially act like a discreet graphics card because system memory will be used less frequently. The combination of the higher clocked graphics core and dedicated sideport memory are what make the 790GX a better performer than the 780G, and what arguably make it the best IGP on the market today, in terms of both features and performance.

One of the 790GX's more interesting features comes by way of the SB750 Southbridge. Dubbed ACC, short for Advanced Clock Calibration, the feature is designed to enhance the overclocking potential of Phenom processors. AMD hasn't revealed exactly how the technology works, but its name and the fact that the Southbridge now has a dedicated link to the CPU, speaks to ACC's ability to keep clock frequencies in sync and stabilize inter-chip communications between the CPU, Northbridge, Southbridge and memory.

To test ACC we overclocked our Phenom X4 9850 processor using the latest version of AMD's Overdrive utility. This particular CPU has trouble running at 2.9GHz on other motherboards, and completed a suite of benchmarks at only 2.8GHz when we first evaluated the chip. With it installed in the Gigabyte MA790GP-DS4H though, with ACC enabled, this very same chip had no trouble hitting 3.1GHz--an effective increase of 600MHz over stock and 300MHz increase over other motherboards that don't feature ACC. That is an impressive feat, and makes this platform the one to own currently if you're an AMD aficionado.

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