But what about frequencies? The BIOS does offer the opportunity to adjust the frequency settings, but for some reason these controls are placed into the Advanced Chipset Features section. We can adjust independently the HyperTransport frequency in the interval from 200MHz to 250MHz and AGP frequency from 66MHz to 100MHz (with 1MHz increment in both cases). There is one more really interesting item in this section called “LDT Speed”, which allows you to set it to 1x, 2x, 2.5x, 3x or 4x. By default it is set to 3x, and when I tried to raise it to 4x, the system would freeze during boot-up. This feature seems to be responsible for the connection speed between the CPU and the mainboard chipset. The resulting clock frequency should be equal to: (200 x LDT Speed) MHz. Bearing in mind that the data is transferred along both signal fronts of the HyperTransport bus and that this bus is 16bit wide each way we obtain the maximum data transfer rate between the chipset and the CPU equal up to 2.4GB/s each way (600MHz x 2 x 2). Note that this peculiarity of the HyperTransport bus is not typical of Shuttle FN85 only. We have heard several times that other NVIDIA nForce3 Pro 150 based mainboards did similar things. It looks as if the mainboard makers (with or without AMD’s recommendations) simplify the mainboard layout to reduce the production costs, believing that 3.2GB/sec in each direction is a way too much, especially since the memory controller is now inside the CPU already.
The memory frequency adjustment on Shuttle FN85 is also implemented in a very interesting way. The entire setting is done by selecting the memory frequency from the list including the following options only: 100MHz, 133MHz, 166MHz and 200MHz. For some reason this option is called Max Memclock and contains a warning that the memory will not work if the frequency is set higher than that. In fact, I do not quite understand what this warning is meant for, because when I set Max Memclock to 200MHz and the HyperTransport frequency to 202MHz, for instance, the memory worked stably at 202MHz (see the CPU-Z report). So, I think that that the name of this feature as well as the warning message are only misleading the users.
Unfortunately, the BIOS of Shuttle FN85 mainboard doesn’t have any opportunities for memory subsystem fine-tuning, in other words, you will not be able to tweak the memory timings at all. At the same time, there is an option called DDR Timing Setting, although enabling or disabling it only affects the ability adjust the memory frequency. I hope that the new BIOS updates will finally allow adjusting the memory timings, too, because it is sometimes as important as the overclocking friendly features of the system.
I was also a little bit upset to find no way to adjust the CPU clock frequency multiplier, because AMD Athlon 64 processors were rumored to have an unlocked clock frequency multiplier. However, the mainboard guys might not implement this opportunity in their products BIOS’s, because AMD doesn’t want them to.
The last interesting feature of the FN85 mainboard used for the new Shuttle SN85G4 barebone system is the availability of only one jumper: Clear CMOS. Note that this jumper is pretty hard to reach when the system is already assembled, although it is not too bad. The tailed cap of this jumper is a really smart idea on Shuttle’s part :)