iXBT Labs - Computer Hardware in Detail






AMD 790GX Chipset

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AMD 780V/780G series launched this Spring turned out quite successful and won mass popularity in various market segments. You can find traditionally inexpensive microATX models for media centers and cheap PCs as well as a new class of well-rigged microATX products (for example, Gigabyte MA78GPM-DS2H) for general-purpose multimedia computers in compact enclosures. The family of full-size ATX boards is growing as well, such boards rarely featured chipsets with integrated graphics before (but those few based on GeForce 6150 and AMD 690G were always popular). In particular, ECS attracted users with democratic prices for its A780GM-A, and Gigabyte surprised them with CrossFire support in MA78G-DS3H.

Meanwhile, users of full-size boards often choose them not only for more expansion slots, but also keeping in mind their better power supply circuits and consequently higher overclocking potential. When you assemble a CrossFire system, you also want your cards to interact in the optimal way (but the second graphics slot in the above-mentioned motherboard from Gigabyte has only four lanes, assigned from the additional lanes, because the chipset itself does not allow to split lanes between graphics ports). To such users we can recommend motherboards on 790X or 790FX chipsets (the latter is the only choice for those who want 16 PCI Express 2.0 lanes for each of two graphics cards or who want configurations with three or four cards). However, both Northbridge and Southbridge were updated since the time these chipsets were released. SB750 certainly looks more attractive than SB600 -- it supports six SATA ports and RAID 5, as well as Advanced Clock Calibration technology, which allows to expand overclocking potential of Phenoms. As for now, only ASUS and Foxconn launched updated modifications of 790FX-based motherboards with the SB750 Southbridge. We all know that manufacturers are rather inert, they are reluctant to add partial modifications to their motherboards.

Taking into account the overclocking potential of the 780G and its tweaks, AMD engineers may have overhauled the graphics core in the chipset to raise its performance. Indeed, it has been done. And the most important thing -- it's now possible to solve the above-listed tasks: built-in CrossFire support; the chipset is now equipped with the new SB750 Southbridge, and motherboard manufacturers were advised to equip such products with voltage regulators for processors with TDP up to 140 W.

Manufacturers apparently had no doubts whether to design motherboards on the new chipset. On one hand, public interest to CrossFire has grown much since the launch of Radeon HD 4850 and 4870. On the other hand, a lot of users, who do not play games very often, are eager to upgrade to motherboards with integrated graphics, provided such motherboards will be rigged up just like discrete models in other respects. So motherboards on AMD 790GX are designed for a wide audience. And now let's have a look at technical characteristics of the new product and see how it fares in our tests.

The integrated graphics core is called Radeon HD 3300. It contains 40 unified shader processors, 4 texture units, and 4 ROPs. Just like in 780G. But the nominal clock rate is higher by 200 MHz. Our tests show that the inner structure has been overhauled as well, because performance gain is higher than can be explained with the difference in frequencies. The chipset allows to install local video buffer SidePort (up to 128 MB of DDR2/DDR3 memory). Unlike motherboards on 780G, this option is actually used in most 790GX-based products. The dedicated unit to decode HD Video, which minimizes CPU load, supports all basic formats, including MPEG2 HD, H.264, and VC1 (nothing to improve here). You can use HDMI, DVI with HDCP, Display Port, and VGA to plug a monitor (depending on what's available in a given motherboard, two monitors can be plugged simultaneously: to any digital and to an analog output). Support for audio output via HDMI is also integrated into the chipset, maximum throughput still allows to output 5.1-channel stream, packed into Dolby Digital, or uncompressed stereo-PCM up to 24 bit/192 kHz. It actually covers practical requirements to plug a TV set (the most popular option) or an inexpensive receiver to a computer media center.

The total number of PCI Express 2.0 lanes is 26 including four lanes for the Southbridge. So the graphics port can support only one graphics card in x16 mode. But unlike the AMD 780G chipset, it's officially possible to install two graphics ports and add CrossFire support. In this case the ports are automatically reconfigured to the x8+x8 mode. Hybrid CrossFire support is also preserved (with Radeon HD 3450 and 3470). However, this mode is unlikely to be used with an expensive card -- active gamers will install at least one powerful card, if they don't have enough money to build CrossFire at once. The others may prefer AMD 790GX to the cheaper 780G because of the increased performance of the integrated graphics core sufficient for casual games.

SB750 features:

  • SATA-II AHCI controller for six SATA300 ports (up to 3 Gbps)
  • RAID support for all SATA ports: 0, 1, 0+1, and 5
  • A single PATA channel for two ATA133 devices
  • 12 x USB 2.0 and 2 x USB 1.1
  • PCI bus (up to six bus master devices)
  • HD Audio 7.1
  • HyperFlash -- it's an option to install flash memory with IDE interface to enable Ready Drive and Ready Boost in Vista
  • Advanced Clock Calibration -- automatic voltage selection for Phenom processors (different for each core) in order to raise overclocking potential or to reduce power consumption in idle mode (for media servers or home theaters)

Performance tests

Testbed configuration

  • Motherboards:
    • ASUS M3N-HT Deluxe BIOS 0901 based on NVIDIA nForce 780a.
    • Gigabyte MA78GPM-DS2H rev. 1.0 BIOS F4 based on AMD 780G
    • Foxconn A7DA-S BIOS P03 based on AMD 790GX
    • ASUS P5E-V HDMI BIOS 0505 based on Intel G35
  • Processors:
    • AMD Athlon 64 X2 4000+
    • AMD Phenom X4 9550
    • Intel Pentium E2160
  • Memory: 2 GB DDR2-800 Corsair XMS2-6400 (DDR2-800, 5-5-5-15-2T)
  • Discrete graphics: ATI Radeon X1900XTX, 512 MB GDDR3
  • HDD: Seagate Barracuda 7200.10 (SATA-II, 7200 rpm)
  • Power supply unit: AcBel ATX-550CA-AB8FB


  • OS and drivers:
    • Windows XP Professional SP2, Windows Vista Ultimate SP1 (32-bit versions)
    • DirectX 9.0c, DirectX 10.1
    • ATI Catalyst 8.9
    • NVIDIA ForceWare 175.19
    • Intel Chipset Drivers
  • Benchmarks:
    • 7-Zip 4.10b
    • XviD 1.0.2 (29.08.2004)
    • Doom 3 (v1.0.1282)
    • FarCry (v1.1.3.1337)
    • Unreal Tournament 2004 (v3339)
    • Futuremark 3DMark06 (1024х768)
    • Serious Sam II 2.07 (Shield Generator28 demo, HDR ON, benchmark)
    • F.E.A.R. (v1.04, Maximum system, Middle graphics)
    • S.T.A.L.K.E.R. (v1.0005, ixbt3 demo)
    • Company of Heroes (v1.2), you can read about settings and image quality in this and other games from this test procedure in the article about AMD 780
    • World in Conflict (v1.0, Low Quality)
    • CyberLink PowerDVD 7.3.2911 (we used only decoders for VC1 and H.264), we played video with Media Player Classic (Home Cinema)

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Article navigation:

Page 1: Introduction, testbed

Page 2: Test results, conclusions

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