AMD’s 790GX chipset

AMD built one heck of a north bridge chip with the 780G. Not only does it feature the fastest integrated graphics core around in the Radeon HD 3200, but the 780G is also capable of full Blu-ray decode acceleration for silky smooth 1080p playback with nominal CPU utilization. The 780G is an energy-efficient affair thanks to advanced 55nm fabrication technology, and it’s loaded with 26 second-gen PCI Express lanes should your gaming aspirations grow beyond modest resolutions and in-game detail levels.

This tiny piece of silicon is so good that AMD’s decided to spin it into a new model: the 790GX. With its graphics core boosted from 500 to 700MHz and the addition of sideport memory riding shotgun, the 790GX is perhaps best thought of as a 780G Type R. The graphics upgrades hit the PCI Express front, too, with the 790GX arriving on motherboards designed to accommodate dual-x8 CrossFire configurations.

The 790GX hasn’t come alone, either. This chipset also brings with it AMD’s new SB750 south bridge chip. This upgraded SB700 adds RAID 5 functionality and an Advanced Clock Calibration (ACC) feature that AMD says allows Phenom processor to overclock higher. Read on for the skinny on ACC, how well it works, and whether AMD has made a great chipset even better with the 790GX.

A new south bridge, with a twist

Unlike the 780G that came before it, the 790GX is not targeted at mainstream audiences. Instead, AMD is gearing this chipset toward the performance and multimedia crowd. That’s an odd segmentation line because the 790GX doesn’t actually bring any new multimedia capabilities to the table. The chip itself is identical to the 780G, so it has the same UVD video block, with full Blu-ray decode acceleration for MPEG2, H.264, and VC-1 formats.

What AMD has done with the 790GX is cherry-picked 780G chips that run comfortably with a 700MHz integrated graphics core. At this new clock speed, the graphics core gets a model number upgrade to the Radeon HD 3300. It also gets sideport memory that AMD has now taken to calling a performance cache. Chipset-integrated Radeons have long supported caches of onboard memory as a faster front line, backed by main memory, but few motherboard makers have taken advantage of the capability. That will apparently change with the 790GX, which has a 16-bit memory interface that can work with either DDR2 or DDR3 RAM.

AMD expects motherboard makers to offer performance caches this time around, and the company says most are likely to use DDR3 memory. Our Gigabyte 790GX board features a 1Gb Elpida EDJ1115BASE-DJ-E DDR3-1333 memory chip, giving the Radeon HD 3300 128MB of local memory that should be quicker to access than reaching out to main memory through the CPU.

Like its Radeon HD 3200 predecessor, the 3300 supports Hybrid CrossFire configurations with Radeon HD 3400 series discrete graphics cards. According to AMD, the 790GX’s graphics clock boost and performance cache memory allow Hybrid CrossFire setups that incorporate a Radeon HD 3470 to offer performance close to that of a Radeon HD 3650. A closer look at the relative cost of each configuration makes that claim considerably less impressive, though. You can find Radeon HD 3650 cards for between $60 and $80 online. Although a Radeon HD 3470 costs only $50, 790GX-based motherboards aren’t going to be cheap. AMD expects most 790GX boards to run around $150, which puts them right in the same price range as boards based on Nvidia’s nForce 750a SLI chipset. The 750a and 790GX are actually quite similar products. Both offer integrated graphics with Blu-ray decode acceleration, and both support their camps’ respective SLI and CrossFire multi-GPU schemes.

Thanks to AMD’s new SB750 south bridge, however, the 790GX has one new trick that the 750a can’t match—Advanced Clock Calibration, or ACC. AMD’s chipset division worked closely with the company’s processor department on this one, gaining an understanding of the Phenom’s low-level CPU interface and then proceeding to exploit it. The SB750 actually connects directly to spare pins on the Phenom CPU, through which it can change internal processor timings. The Phenom’s factory defaults are designed for stock frequency thermals, but through ACC, they can be tweaked for better over- or underclocking.

Citing “competitive reasons,” AMD won’t be more specific about exactly how ACC fiddles with Phenom’s dials. With the requisite car analogy, AMD likens its approach to taking a normal, street-going car and tuning it up for the track. Changing the Phenom’s default timings apparently won’t curtail the processor’s expected lifespan—or at least no more than overclocking does all on its own. AMD is, of course, quick to point out that overclocking success can vary from one CPU to another, but it expects ACC to bolster a processor’s top speed by at least 200MHz.

A 200MHz processor clock boost thanks to a south bridge upgrade would be very special sauce indeed, and we’ll see how it pans out with our own Phenom X4 9850 Black Edition in a moment. For now, let’s turn our attention back to the SB750. This is actually a new chip, but apart from ACC, we’re looking at the same core logic as the SB700, which is essentially a die-shrunk SB600. Unfortunately, AMD’s longstanding issues with AHCI Serial ATA controller configurations persist in the SB750, all but forcing users to run the south bridge in plain old IDE mode. That’s not the end of the world, but IDE mode doesn’t support Serial ATA perks like hot swapping and Native Command Queuing.

AMD 790GX Nvidia nForce 750a SLI
Processor interface
16-bit/2GHz HyperTransport
16-bit/2GHz HyperTransport

PCI Express 2.0 lanes


Multi-GPU support

2-way SLI

Chipset interconnect

PCIe 1.1 x4
Interconnect bandwidth
Serial ATA ports 6 6
Native Command Queuing
RAID 0/1
RAID 0+1/10
ATA channels
Max audio channels
Audio standard
USB ports 12 12

Rather than addressing the AHCI issue, AMD turned its attention to the SB750’s RAID functionality. Support for RAID 5 arrays has been added to the mix, and AMD claims it can easily outrun Intel’s ICH10R with three-drive arrays, although oddly, not with four-drive configs.

That’s it for new south bridge features in the SB750. The chip really only needed RAID 5 support to achieve parity with the nForce 750a, and the 790GX has more PCI Express 2.0 lanes than the nForce, anyway. Keep in mind that four of those lanes are consumed by the 790GX’s chipset interconnect, though; only 22 PCIe lanes are available for onboard peripherals and expansion slots.

Gigabyte’s GA-MA790GP-DS4H motherboard
Yet another crossover vehicle

Manufacturer Gigabyte
Model GA-MA790GP-DS4H
Price (MSRP) $150
Availability Soon

The first 790GX-based motherboard to hit our labs was Gigabyte’s GA-MA790GP-DS4H, whose $150 MSRP fits right in line with AMD’s expectations for the platform. Unlike most integrated graphics mobos, the DS4H is not a Micro ATX board. It fits into a full ATX form factor that looks very much like any other mid-range desktop motherboard. Rather than simply beefing up existing integrated graphics options, the 790GX looks destined to bring integrated graphics to enthusiast-class ATX designs.

With full ATX real estate to work with, Gigabyte’s engineers had plenty of room to squeeze in additional slots and ports that might not have otherwise fit on a smaller footprint. And they’ve gone to town, with varying levels of success. One of my personal pet peeves is power plug placement, and that’s been done quite well. The auxiliary 12V connector is located along the top edge of the board where cabling won’t obstruct chassis exhaust airflow. The primary power connector is also located close to the top edge of the board in what is an almost perfect layout for traditional case designs. However, you may need an extension cable or two if you run one of those new-fangled upside-down enclosures.

Power is an important part of the 790GX equation in light of the fact that most 780G boards are ill-equipped to handle high-TDP Phenoms. Black Edition chips with unlocked upper multipliers remain the most attractive Phenoms in AMD’s lineup, but the X4 9850 and 9950 carry respective TDPs of 125 and 140W—too much power for even some mid-range motherboards to handle.

Since AMD recently bumped up Phenom wattages with the 9950, it’s no surprise that the company worked closely with motherboard makers to ensure that 790GX boards support 140W processors. A chip that consumes that much power is going to run pretty hot, as well, so it’s good that Gigabyte has left plenty of room around the DS4H’s CPU socket for gargantuan coolers. We use a Scythe Ninja heatsink to test massive cooler compatibility here in the Benchmarking Sweatshop, and it just fits on the Gigabyte board as long as you use standard-height memory modules. DIMM slot clearance for huge heatsinks is a common problem for Socket AM2 motherboards, likely because motherboard makers strive to maintain short trace lengths between memory modules and the processor’s on-die memory controller.

At least there are no clearance issues associated with the onboard heatsinks. The DS4H has a passive north bridge cooler piped up to a substantial VRM heatsink, but neither is obnoxious enough to get in the way.

The chipset’s south bridge cooler is an unobtrusive affair, as well; its low-profile design leaves plenty of room for longer graphics cards. However, lengthy double-wide cards can wreak havoc on the board’s Serial ATA connectivity. Plug one into the second PCI Express slot, and you’ll obscure access to not one, not two, not even three, but all six SATA ports. This is essentially a CrossFire-only issue, since there’s no other reason to run a double-wide card in the board’s second x16 slot, but it’s the sort of problem that someone should have caught long before this board design was finalized.

True to the 790GX’s CrossFire support, the DS4H comes with a pair of physical PCIe x16 slots capable of running a pair of graphics cards in a dual-x8 lane configuration. This graphics expansion capacity is backed by three PCI Express x1 slots and a couple of standard PCI slots.

While it’s fair to note here that the 790GX’s CrossFire support is limited to a dual-x8 implementation, the nForce 750a faces a similar dual-x8 SLI limitation and we found that doesn’t significantly hamper its performance. I suspect CrossFire will be similarly unfazed by what is—thanks to PCIe 2.0’s faster signaling rate—essentially the same bandwidth you get from a dual-x16 setup with gen-one PCI Express.

A trio of graphics outputs dominates the DS4H’s port cluster. HDMI makes an appearance, of course, and it’s joined by VGA and DVI outputs. Gigabyte also throws in a digital S/PDIF audio output linked to an ALC889A codec chip that can encode Dolby Digital Live bitstreams on the fly. SoundStorm’s most coveted feature has taken up residence in a Realtek codec chip; surely that’s a sign of the impending apocalypse.

The Gigabyte board’s port cluster is otherwise adorned with the usual mix of analog audio, Ethernet, Firewire, and USB ports. We’d like to see more USB connectivity here, especially since there are onboard headers for an additional eight ports. eSATA wouldn’t have been a bad idea, either.


The Micro ATX boards common with integrated graphics chipsets can get by being a little light on BIOS options because they’re mainstream products targeted at folks who generally don’t fiddle with clock speeds, multipliers, or memory timings. But the 790GX is supposed to be a performance product, so its BIOS has to measure up.

Bus speeds
CPU base clock:
200-500MHz in
1MHz increments

PCIe: 100-200MHz in 1MHz increments

HT: 200-2600MHz in 200MHz
GPU: 200-2000MHz in 1MHz increments

Bus multipliers
CPU: 5-25X in 0.5X
Memory controller: 5-16X in 1X increments
DRAM: 2, 2.66,
3.33, 4, 5.33
Voltages CPU:
+/-0.6V in 0.025V increments
+/-0.6V in 0.025V increments

+0.05-0.55V in 0.05V increments

NB: -0.2-+0.3V in 0.025V increments

SB: +0.1-0.3V in 0.1V increments

+0.1-0.3V in 0.1V increments

Voltage, fan
status, and temperature monitoring

Fan speed control
CPU, system

Gigabyte consolidates the bulk of the DS4H’s tweaking and overclocking options on a single page. Unlike most Gigabyte BIOSes, these options aren’t gated by a secret Ctrl+F1 handshake. The only options that appear to be hiding this time around are those associated with Advanced Clock Calibration, which should probably be left on auto anyway.

The rest of the BIOS stacks up as one might expect. CPU base clock options are available up to 500MHz, although you’re much better off overclocking with a Black Edition processor that supports upwards multiplier manipulation. Control over the Phenom core multiplier is available in 0.5X steps, and users can adjust the processor’s north bridge multiplier in 1X steps. Integrated graphics core overclocking is also supported, if you’re into that sort of thing. To me, though, that makes about as much sense as strapping a nitrous kit to a Toyota Yaris.

Processor overclocking is a much better use of your time, and the DS4H will let you crank CPU voltages by up to 0.6V. You can also drop the core voltage by 0.6V if underclocking is more your style, and the BIOS yields similar control over the CPU’s north bridge voltage. DRAM voltages scale up by up to 0.55V, too, and users can tweak not only the voltage of the chipset’s north and south bridge elements, but of the board’s sideport memory, as well.

Access to all the usual memory timings is included, as one might expect, and Gigabyte even kicks in a measure of automatic fan speed control. Users can choose between three- and four-pin processor fan modes, and temperature-based fan speed control extends to the board’s system fan header. Unfortunately, the BIOS doesn’t yield much actual control over the automatic fan speed, er, control. We’d like to see Gigabyte offer the ability to set target processor and system temperatures and to specifically define fan voltage settings.

A new OverDrive utility

AMD is ushering in the 790GX with a new version of its OverDrive tweaking utility. This app gets a menacing all-black skin and it has been updated to bring ACC controls to Windows.

OverDrive can be used to tweak system voltages and multipliers without dipping into the BIOS. Users can even set independent multipliers for each Phenom CPU core, should some cores be more comfortable at higher speeds than others. ACC can be enabled on this page, too, although doing so requires a reboot.

In addition to plenty of overclocking options, OverDrive also serves up a full suite of memory timing controls that should let you tune to your heart’s content. There are more timing options here than even most enthusiasts would know what to do with.

OverDrive isn’t just a tweaking and overclocking app, either. AMD has built in a hardware monitoring tools that allows you to keep tabs on each Phenom core alongside a suite of GPU and motherboard variables.

Specifics on specifications

As ever, we’ve whipped up a handy quick-reference specifications chart on the Gigabyte GA-MA790GP-DS4H for your viewing pleasure.

CPU support
Socket AM2/AM2+ Phenom,
Athlon X2 processors

North bridge

South bridge

PCI Express 2.0 (16MB/s)

Expansion slots
2 PCI Express x16

3 PCI Express x1
2 32-bit/33MHz PCI

4 240-pin DIMM

Maximum of 8GB of DDR2-533/667/800/1067 SDRAM

Storage I/O
Floppy disk

1 channel ATA/133

6 channels 300MB/s Serial ATA with RAID 0, 1, 0+1, 5 support

Audio 8-channel HD audio via Realtek
ALC889A codec
Ports 1 PS/2 keyboard
1 PS/2 mouse

2.0 with headers for 8 more

1 RJ45 10/100/1000 via Realtek RTL8111C
1 1394a Firewire via Texas
Instruments TSB43AB23 with headers for 2 more
1 DVI out
1 VGA out
1 HDMI out

1 front out
1 analog bass/center out

1 analog rear out

1 analog surround out

1 analog line in

1 analog mic in
1 digital TOS-Link S/PDIF out

Asus’ M3A78-T motherboard

Less than 12 hours before the deadline for this review, an Asus M3A78-T motherboard arrived on my doorstep. Naturally, I didn’t have time to run this board through our gauntlet of performance tests. I did, however, have just enough time to snap a picture and give the board a quick once-over.

The M3A78-T doesn’t have SATA port clearance issues like the Gigabyte board, and it has a third PCI Express x16 slot. eSATA connectivity is included, as well, and Asus throws in a 128MB DDR3-1333 performance cache for the Radeon HD 3300. Other notable features include Gigabit Ethernet networking courtesy of Marvell, a Firewire chip from LSI, and a Realtek ALC1200 codec chip that mysteriously isn’t listed on the company’s website. Typical Asus perks like a built-in Express Gate Linux install and front panel jumper blocks round out the package.

Asus says the M3A78-T carries a suggested retail price of $159, which makes it a little more expensive than the Gigabyte board we’re testing today.

Our testing methods

The 790GX’s unique blend of what should be scary-fast integrated graphics with a full ATX form factor that boasts CrossFire compatibility makes it a little hard to classify. The fact that board prices are expected to ring in around the $150 makes matters a little easier, since that’s exactly the price range of motherboards based on Nvidia’s similarly-equipped nForce 750a SLI platform.

Given AMD’s unresolved AHCI issues, we’ve tested the 790GX with the south bridge’s Serial ATA controller running in IDE mode. The nForce 750a has no problems running in AHCI mode, which is how we tested it. Both platforms were run using their integrated graphics as the primary output. We also ran an additional set of application performance and power consumption tests with a discrete GeForce 9800 GTX installed.

All tests were run three times, and their results were averaged.


Phenom X4 9850 Black Edition
System bus 2GHz HyperTransport

Gigabyte GA-MA790GP-DS4H

XFX MD-A72P-7509
Bios revision F1 1.0

North bridge
AMD 790GX Nvidia nForce 750a SLI

South bridge
Chipset drivers Catalyst 8.521.1 ForceWare 18.11
Memory size 2GB (2 DIMMs 2GB (2 DIMMs)

Memory type

Corsair CM2X2048-8500C5 DDR2 SDRAM
at 714MHz
CAS latency
4 4
delay (tRCD)
4 4
RAS precharge
4 4
Cycle time
12 12
Command rate 2T 2T

Audio codec
with 1.99 drivers
with 1.99 drivers

GeForce 8800 GT 1GB PCIe
with ForceWare 177.79 drivers
Hard drive
Western Raptor X 150GB

Windows Vista Ultimate x86
with Service Pack 1

Thanks to Corsair for providing us with memory for our testing.

All of our test systems were powered by OCZ GameXStream 700W power supply units. Thanks to OCZ for providing these units for our use in testing.

Finally, we’d like to thank Western Digital for sending Raptor WD1500ADFD hard drives for our test rigs.

We used the following versions of our test applications:

The test systems’ Windows desktop was set at 1280×1024 in 32-bit color at an 85Hz screen refresh rate. Vertical refresh sync (vsync) was disabled for all tests.

All the tests and methods we employed are publicly available and reproducible. If you have questions about our methods, hit our forums to talk with us about them.

Memory performance

Our 790GX platform has slightly more memory bandwidth than the 750a when both are running their integrated graphics, but the tables turn when we swap in a discrete graphics card. Of course, both chipsets are sharing the same on-die Phenom memory controller here.

Motherboards don’t always handle four DIMMs gracefully, so we popped an additional two memory modules into each system for another round of tests.

Little changes when we move up to four DIMMs.

The following latency graphs are a little indulgent, so I won’t be offended if you skip them. They show access latencies across multiple block and step sizes, painting a fuller picture of memory controller performance with each chipset. Yellow represents L1 cache, light orange is L2, red is L3, and dark orange is main memory.

When you’re running the same Phenom memory controller paired with the same memory running at identical timings, there isn’t a whole lot of variety in memory access latency.

STARS Euler3d computational fluid dynamics

Few folks run fluid dynamics simulations on their desktops, but we’ve found this multi-threaded test to be particularly demanding of memory subsystems, making it a good link between our memory and application performance tests.

The 790GX pulls up a little short in Euler3d, falling behind the 750a with both discrete and integrated graphics configurations.


WorldBench uses scripting to step through a series of tasks in common Windows applications. It then produces an overall score. WorldBench also spits out individual results for its component application tests, allowing us to compare performance in each. We’ll look at the overall score, and then we’ll show individual application results alongside the results from some of our own application tests.

While the 790GX running its integrated Radeon HD 3300 enjoys a higher overall WorldBench score than the equivalent nForce setup, the green team is a hair quicker with a discrete graphics card installed. Let’s break down the results for a more detailed look.

The integrated graphics platforms are clearly slower in WorldBench’s Movie Creator and Windows Media Encoder tests, but the 790GX and 750a are similarly handicapped. In the Photoshop test, however, both 790GX configs are slower than the 750a.

Our integrated graphics options remain a little slower through WorldBench’s office and multitasking tests, and again, the 790GX just trails its nForce competition.

The results of WorldBench’s 3ds max DirectX modeling test are curious, to say the least. The 790GX tops all contenders here, including our discrete graphics configurations.

And there are more intriguing results. For whatever reason, WorldBench’s Nero test clearly favors our discrete graphics setups. There’s little performance difference between the 790GX and 750a, though. The results of the WinZip test are a little harder to interpret because Windows Vista’s propensity to juggle drive contents seems to impact performance in that test.


This first batch of gaming tests was run at resolutions and detail levels that go beyond what we’d expect integrated graphics processors to be able to handle. We’ve included them to illustrate just how much more performance can be had from a mid-range graphics card like the GeForce 9800 GTX.

Clearly, serious gamers are much better off with real graphics cards. But the 790GX’s Radeon HD 3300 fares remarkably well here, and it’s certainly playable in Quake Wars and Episode Two. The nForce 750a’s integrated graphics component doesn’t even come close.

Integrated graphics performance

For this next set of tests we’ve relaxed our display resolutions and in-game detail levels to more accurately reflect settings that run well with the limited horsepower available in integrated graphics solutions.

Yeah, the Radeon HD 3300 pretty much rocks. The nForce 750a doesn’t have Nvidia’s fastest integrated graphics core, but even if it did, our experience with the GeForce 8300 shows that the 790GX would still be miles ahead.

Serial ATA performance

The Serial ATA disk controller is one of the most important components of a modern core logic chipset, so we threw each platform a selection of I/O-intensive storage tests using a Western Digital Raptor WD1500ADFD.


We’ll begin our storage tests with IOMeter, which subjects our systems to increasing multi-user loads. Testing was restricted to IOMeter’s workstation and database test patterns, since those are more appropriate for desktop systems than the file or web server test patterns.

The fact that we’re forced to run the 790GX’s storage controller in IDE mode, thus losing out on Native Command Queuing, hurts the chipset’s performance here. The 750a offers higher throughput at nearly every load level.

Our IOMeter response time results aren’t nearly as stark, but the nForce delivers quicker response times across multiple load levels.

At least in IOMeter, the CPU utilization of these two systems is essentially identical.

HD Tach

We used HD Tach 3.01’s 8MB zone test to measure basic SATA throughput and latency.

The results of HD Tach’s burst and sustained read speed tests are close, but the nForce opens up a big lead on the 790GX in the sustained write speed test. We’ve noticed that this test favors storage controllers that support Native Command Queuing, which explains the 790GX’s dismal showing.

AMD does eke out a small lead in the access time test, where the 790GX shaves 0.3 milliseconds off the nForce 750a’s random access time.

HD Tach’s margin of error for the CPU utilization test is +/- 2%, and our scores are within that range, making this one too close to call.

USB performance

Our USB transfer speed tests were conducted with a USB 2.0/Firewire external hard drive enclosure connected to a 7200RPM Seagate Barracuda 7200.7 hard drive. We tested with HD Tach 3.01’s 8MB zone setting.

AMD’s south bridge chips have never offered the best USB performance, and the SB750 is no exception. The nForce easily outguns the 790GX here.

PCI Express performance

We used ntttcp to test PCI Express Ethernet throughput using a Marvell 88E8052-based PCI Express x1 Gigabit Ethernet card.

Although the 750a and 790GX offer equivalent throughput here, the AMD chipset’s CPU utilization is a little higher.

PCI performance

To test PCI performance, we used the same ntttcp test methods and a PCI VIA Velocity GigE NIC.

Yeah, we couldn’t get our VIA Velocity-based Gigabit Ethernet card working in the Gigabyte 790GX board. The card was detected in both slots, but Vista refused to install not only its own embedded drivers for the card, but the latest standalone driver package, as well. This is likely a compatibility quirk associated with the motherboard and early BIOS revisions rather than a problem with the 790GX chipset.

Power consumption

We measured system power consumption, sans monitor and speakers, at the wall outlet using a Watts Up Pro power meter. Power consumption was measured at idle and under a load consisting of a multi-threaded Cinebench 10 render running in parallel with the “rthdribl” high dynamic range lighting demo.

AMD chipsets have long consumed less power than their nForce counterparts, but that isn’t the case with the 790GX. These results are surprising to say the least, especially given that AMD says it employed power-saving BIOS and driver tweaks developed for its Puma notebook platform in the 790GX. However, it is worth noting that our 750a-based motherboard is a relatively barebones affair with only a four-phase power solution (that doesn’t officially support processor wattages above 95W) and no Firewire. The 790GX is running not only a much faster integrated graphics component, but also an onboard 128MB performance cache.


We haven’t had much success overclocking our Phenom X4 9850 Black Edition, so we were eager to see whether AMD’s fancy Advanced Clock Calibration would have an impact. To kick things off, we overclocked the CPU by raising the core multiplier on all four cores in 0.5X steps using AMD’s OverDrive utility. Stability was tested at each step with a four-way Prime95 load.

As expected, our chip didn’t fare so well. It cruised up to a 13.5X multiplier with little problem, yielding a stable 2.7GHz clock speed. However, running the CPU at 2.8GHz produced Prime95 errors on one core, and no amount of additional voltage was able to stabilize the chip at that speed.

Next, we enabled ACC, set it to auto, and resumed our pursuit of higher speeds. Much to our surprise, 2.8GHz wasn’t a problem, even with the default CPU voltage. 2.9GHz required a voltage bump to 1.3375V, but it was stable. And so was 3.0GHz with a 15X multiplier. 3.1GHz, however, proved elusive no matter how much we fiddled with voltages.

ACC definitely works, then. We were able to squeeze an extra 300MHz from our Black Edition Phenom with what amounts to a modest voltage increase. Do keep in mind that overclocking success is never guaranteed, though.

Motherboard peripheral performance

Core logic chipsets integrate a wealth of peripherals, but they don’t handle everything. To provide a closer look at the peripheral performance you can expect from the motherboards we’ve tested today, we’ve complied Ethernet and audio performance results below.

NTttcp Ethernet

Throughput (Mbps)
CPU utilization (%)

Gigabyte GA-MA790GP-DS4H
938 9.5

XFX MD-A72P-7509
932 8.3

Realtek’s finally built a decent Gigabit Ethernet chip in the RTL8111C, which the Gigabyte board uses to deliver excellent throughput with low CPU utilization.

HD Tach
Firewire performance

Read burst

speed (MB/s)

Average read

speed (MB/s)

Average write

speed (MB/s)

CPU utilization


Gigabyte GA-MA790GP-DS4H
42.1 37.4 23.4 1.3

XFX MD-A72P-7509

Our 750a motherboard doesn’t have a Firewire chip, so it’s riding the pine in this test. The DS4H’s Firewire performance is quite good, though.

RightMark Audio
Analyzer audio quality

Overall score

Frequency response

Noise level

Dynamic range


THD + Noise

IMD + Noise

Stereo Crosstalk

IMD at 10kHz

Gigabyte GA-MA790GP-DS4H
4 5 5 5 3 1 3 6 3

XFX MD-A72P-7509
4 5 3 3 3 1 3 4 3

We’ve switched to RMAA loopback tests that route a motherboard’s stereo output through its line input, and the Gigabyte board scores higher than the XFX in several tests. That isn’t enough to break a tie in the overall RMAA score, though.


AMD’s 790GX is the fastest integrated graphics chipset on the market. Period. The 780G’s Radeon HD 3200 was already faster than the best the competition had to offer, and with a 200MHz core clock boost and the addition of performance cache memory, the Radeon HD 3300 offers even better frame rates. Throw in Blu-ray decode acceleration and HDMI output and you have the recipe for the ultimate integrated graphics platform, right?

Not quite.

The 790GX may have the best integrated graphics component on the market, but it’s also only available on $150 motherboards. The 780G has the exact same video decoding block and (albeit slower) graphics core, but it can be had on motherboards that cost less than $90. That $60 price difference is just enough to score a Radeon HD 3650 that even AMD admits offers better performance than the combination of the 790GX and a Radeon HD 3470 in Hybrid CrossFire. If you want better game performance, then, you’re better off spending your money on a discrete graphics card. In the absence of something akin to the HybridPower tech available on Nvidia’s nForce 750a SLI chipset, which can power down discrete graphics cards and switch to the motherboard GPU at idle, the Radeon HD 3300’s appeal is largely irrelevant if you’re using a standalone graphics card.

At least the 790GX is more than just a hopped up integrated graphics processor. The most interesting element of the chipset for enthusiasts may be the Advanced Clock Calibration capabilities built into the new SB750 south bridge. AMD’s ATI acquisition pays big dividends here, allowing the SB750 to reprogram internal Phenom processor timings to improve overclocking. With our X4 9850 Black Edition, ACC is good for a 300MHz clock speed boost, and that’s not bad at all.

ACC isn’t going to be unique to the 790GX, either. Some motherboard makers will be pairing the SB750 with AMD’s existing 790FX north bridge chip, which lacks integrated graphics but packs enough PCI Express lanes for dual-x16 CrossFire implementations (and four-way-x8 configs). To me, that pairing makes a lot more sense than the 790GX—it’s tuning a sports car for the track rather than what feels like an all-things-to-all-people crossover subcompact.

And that neatly brings us to the crux of the problem with the 790GX. The chipset’s components parts have impressive qualities, but when combined together, they pull it in opposite directions. $150 is going to be too expensive for most folks who are looking at running integrated graphics, particularly when better gaming performance can be had for less, and the Radeon HD 3300 with its fancy performance cache will essentially be waste for anyone running a discrete graphics card.

The 790GX’s appeal for enthusiasts may ultimately hinge on how many 790FX boards pick up the SB750, and more importantly, how much they cost. If 790FX/SB750 combos tip up in the $180-200 range, 790GX mobos like Gigabyte’s GA-MA790GP-DS4H will be good mid-range options for Phenom overclockers looking to get their hands on ACC. The DS4H has everything you’d want in a mid-range enthusiast board, including support for 140W Phenoms, digital audio output with Dolby Digital Live encoding, and CrossFire compatibility. It just also happens to have a swanky integrated graphics core that looks a little out of place.

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