In Figure 1 you can have a good look at ECS A790GXM-A. Pay attention and you will see another model name printed on it: “ES780DM-A,” which is the name ECS was using before the official launch of AMD 790GX chipset. It is a socket AM2+ motherboard, meaning that it supports the new HyperTransport 3.0 and the “split plane” technologies used by AMD CPUs based on K10 architecture (i.e., Phenom CPUs). For more information read our Inside AMD K10 Architecture tutorial.

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Figure 1: ECS A790GXM-A motherboard.

The first thing that caught our eye was the size of this motherboard. Usually motherboards with on-board video use the microATX form factor, but ECS A790GXM-A is an exception, using the regular ATX form factor. Motherboards based on AMD 790GX from other manufacturers should follow the same size. Also, motherboards with on-board video usually provide only one PCI Express x16 slot for you to install a “real” video card if you are not pleased with the performance provided by the integrated video processor – some motherboards don’t even have this option –, but ECS A790GXM-A provides not only one but two PCI Express 2.0 x16 slots (running at x8 if both are used at the same time). This allows you to add two discrete video cards under CrossFire mode. Other motherboards based on AMD 790GX will also follow this configuration.

The chipset supports Hybrid Graphics technology, which allows certain low-end video cards like Radeon HD 3450 to work in parallel with the on-board video in CrossFire mode, which provides a higher performance than a single add-on graphics card alone (read our SLI vs. CrossFire tutorial for a complete list of compatible cards).

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Figure 2: Motherboard slots.

Besides the two PCI Express 2.0 x16 slots, this board also provides two x1 PCI Express slots and two regular PCI slots.

This motherboard requires a standard peripheral power connector installed on the motherboard (see Figure 2) for feeding the add-on video cards.

Another feature that differentiates this motherboard from low-end ones is the fact that its on-board video uses a dedicated 128 MB memory chip to be used as video memory. As you know the most common architecture used by motherboards with on-board video is called UMA, Unified Memory Architecture, where the chipset “steals” part of the RAM to be used as video memory. This motherboard will still use the UMA architecture if the video processor requires more than 128 MB of video memory. Using a dedicated chip instead of stealing part of the RAM also improves video performance, at least in theory – we will see if this holds true during our benchmarks.

This architecture is called “Side Port” by AMD and on ECS A790GXM-A a Samsung K4N1G164QQ-HC25 1 Mbit GDDR2 chip is used (1 Mbit = 128 MB). The official maximum clock rate supported by this chip is 400 MHz (800 MHz DDR) and on this motherboard this chip is really accessed at 400 MHz (800 MHz DDR). On the motherboard setup you can decrease the speed used to access this memory, but not increase.

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Figure 3: Dedicated memory chip for video memory.

This motherboard has two independent video outputs, one VGA and one HDMI (supporting audio), making it a good choice for a home theater PC (HTPC).

Another highlight from this motherboard is the presence of four memory sockets. Usually low-end motherboards have only two memory sockets, so having four of them on this board is a blessing, as it will help you adding more memory in the future without needing to replace your current memory modules.

It is always good to remember that with AMD processors the memory controller is embedded inside the CPU, so the amount and types of memory the system supports depend on the CPU, not on the motherboard. Socket AM2 and AM2+ processors support only DDR2 memories, with AM2 processors (i.e., Athlon X2) supporting up to DDR2-800 and with AM2+ processors (i.e., Phenom) supporting up to DDR2-1066.

All socket AM2/AM2+ CPUs support dual-channel feature so for the best performance you must install two or four memory modules (do not install just one memory module). For enabling dual-channel feature you must install the modules on sockets with the same color, if you are installing two modules.