ASUS M3A32-MVP DeLuxe/WiFi-AP is today the most high-end motherboard for the AMD platform money can buy. Based on the new AMD 790FX chipset this board is targeted to the AMD gaming platform “Spider,” featuring four PCI Express x16 slots allowing up to four video cards working in parallel through the new CrossFireX interconnection mode. As other motherboards from ASUS, this product has passive heatsinks, but what is unique about it is that it comes with a passive heatsink for the memory modules that can be attached to the motherboard passive cooling solution. This board also features an 802.11g (54 Mbps) WiFi access point, allowing you to share your Internet connection wirelessly without a wireless broadband router, eSATA port, coaxial and optical SPDIF outputs and much more, so read on.
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Figure 1: ASUS M3A32-MVP DeLuxe/WiFi-AP motherboard.
This motherboard is a socket AM2+ board. There are two main differences between socket AM2 and socket AM2+: the support for HyperTransport 3.0 and Dual Dynamic Power Management (DDPM) technology, present on AMD CPUs based on K10 core (e.g., Phenom CPUs). You can still install Phenom on socket AM2 motherboards but you won’t have these two technologies available and the CPU will talk to the chipset only up to 2,000 MB/s (HyperTransport 2.0) instead of up to 10,400 MB/s (HyperTransport 3.0) – it is important to notice that current Phenom processors work under the lowest HyperTransport 3.0 transfer rate, 7,200 MB/s. For more information about those technologies we recommend you to read two other articles, Inside AMD K10 Architecture and The HyperTransport Bus Used by AMD Processors.
AMD 790FX is the latest and most high-end chipset by AMD/ATI, using ATI’s SB600 southbridge, which is the same south bridge chip used by ATI Radeon Xpress 3200 chipset. AMD 790FX brings three new important features. The first is of course the support of HyperTransport 3.0, allowing the communications between the chipset and the CPU to be performed at a higher speed – if a HT3-based CPU is installed on the system, of course; otherwise, i.e., if you install a plain socket AM2 Athlon 64, the maximum transfer will be 2,000 MB/s. HyperTransport 3.0 maximum transfer rate is of 10,400 MB/s (this rate is also called 5,200 MT/s) but Phenom CPUs released so far have their HyperTransport bus working at 7,200 MB/s (3,600 MT/s). It is important to remember that since on AMD CPUs the memory controller is embedded on the CPU and not on the chipset this transfer rate is available for I/O transfers only.
The second biggest feature of this new chipset is its support for the new PCI Express 2.0 bus, which doubles the bandwidth available for video cards from 2.5 GB/s to 5 GB/s, if they are also based on PCI Express 2.0 (so far the only PCI Express 2.0 video cards available are GeForce 8800 GT, Radeon HD 3850 and Radeon HD 3870). This chipset provides 32 PCI Express 2.0 lanes for graphics, which can be arranged as two PCI Express 2.0 x16 slots truly working at x16 or four PCI Express 2.0 x16 slots working at x8. More on this in a minute.
The third biggest feature is the support for CrossFireX, which allows up to four video cards based on this new connection working in parallel.
This motherboard features four PCI Express 2.0 x16 slots, which are physically identical to PCI Express 1.0 x16 slots, so you can install PCI Express 1.0 cards without any problem. If one or two cards are installed, the slots work at x16. If a third video card is installed, the first slot will remain working at x16, but the other two slots will work at x8. And if you install four video cards all slots will work at x8.
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Figure 2: Four PCI Express 2.0 x16 slots.
As you can see in Figure 2 this motherboard has two standard PCI slots and no PCI Express x1 slots.
Keep in mind that if you use an AMD CPU that isn’t based on HT3 you will limit the graphics performance of your system. Let’s do some math to explain this better.
The maximum bandwidth between AMD 790FX chipset and the video cards is of 10 GB/s (5 GB/s, which is the x16 transfer rate, times two), if PCI Express 2.0 video cards are used. If PCI Express 1.0 cards are used, the maximum bandwidth available is of 5 GB/s (2.5 GB/s, which is the x16 transfer rate, times two).
In theory HyperTransport 3.0 offers a maximum transfer rate of 10 GB/s, what would match perfectly the required bandwidth if you use two or more PCI Express 2.0 video cards. However Phenom processors released so far use a lower 7 GB/s transfer rate, generating a bottleneck. This bottleneck does not exist if you use PCI Express 1.0 video cards, as the maximum required bandwidth will be of 5 GB/s.
But if you use an Athlon 64 CPU, for example, you will limit the graphics performance. Since this CPU can talk to the chipset only up to 2 GB/s you won’t be able to achieve the maximum performance video cards are capable of delivering. In fact, even on regular socket AM2 motherboards with PCI Express 1.0 this occurs, as the maximum I/O transfer rate of the CPU is of 2 GB/s and the maximum graphics transfer rate if of 2.5 GB/s if one video card is used or 5 GB/s if two cards are installed.
So HyperTransport 3.0 unlocks the maximum graphics performance of your system, even though for a perfect system we still need to wait for the release of Phenom CPUs based on the 10 GB/s HyperTransport bus.
However the numbers provided above are theoretical and in fact no performance impact may be seen, as video cards transfer data at a rate far below their maximum theoretical transfer rates.