Shuttle XPC ST61G4 SFF barebones PC

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The ST61G4 uses a Shuttle FT61 motherboard with the ATi 9100 IGP chipset. The IGP 9100 competes directly with Intel's 865G chipset but offers much better onboard video performance. The IGP 9100 consists of the RS300 northbridge and the IXP150 southbridge. The NB chip is actively cooled on this board, with a 40mm fan atop the small HS. This is not a welcome sight for those seeking low noise.

As with the Zen, most of the plug-ins are near the front left, where they are easy to access with the dive cage off. It's also the location of the CMOS memory clear jumper. But the SATA drive connectors and the floppy drive connector are both in the back.

The optical and hard drives are installed and plugged in, along with the CPU, HSF and memory chips.
A single IDE cable was used to connect both the HDD and optical drives.

As the specifications indicate, this system is compatible with Intel Socket 478 processors on a 400, 533, or 800MHz front-side bus, giving a wide range of CPU choices from high-end P4s to low-end Celerons. This chipset also supports Hyper-Threaded processors and dual-channel memory for up to 2GB of PC3200 SDRAM. The IXP150 southbridge supports six USB 2.0 ports, four of which are external plus the two internal headers for the integrated card reader.

There is also support for two ATA-100 P-ATA IDE channels and two Serial ATA channels; the latter is not included in the Zen. SATA is provided by the Silicon Image 3512 chip, with Raid 0/1 function and support up to 1.2Gb/s (150MB/S).

The Radeon 9100 Integrated Graphics Processor supports DirectX 8.1 and utilizes a 128-bit DDR memory bus running at 300MHz. This should be powerful enough for HTPC's, business systems and non-hardcore gaming. The 9100 IGP has single VGA and S-Video outputs, but no built-in DVI output or multi monitor support. That's what the AGP slot is for.

The AGP slot is located closer to the outer edge of the board than the single PCI slot, due to the need for VGA cards to clear the drives and cages midway up the length of the case. This is a standard location for AGP slots in SFF systems. It means that dual-width cooling VGA systems such as the Zalman heatpipe coolers or the Arctic Cooling VGA Silencer simply cannot be used.


Line the Zen, the ST61G4 BIOS has five fan settings, starting with Smart Fan mode that allows the threshold temperature to be set manually. If set to 60°C, for example, the fan stays at minimum speed and does not ramp up until this CPU temperature is reached. There are four others, as shown in the screen below: Ultra Low, Low, Mid, and Full.

The second relevant BIOS setting for noise control is Vcore, the core voltage of the CPU. Overclockers raise Vcore to keep the CPU stable while it's running higher than the rated speed. The price is a big increase in CPU heat because power dissipation varies with the square of the voltage, which is an exponential relationship between voltage and heat.

PC silence enthusiasts know this relationship well and use judicious drops in Vcore to make the CPU run much cooler. Almost every CPU I've ever used has been perfectly stable with 0.1V less than standard voltage, and the temperature drop is usually 2~3°C. So how undervoltable is the ST61G4? Very underclockable, in 0.125V increments all the way down below 0.9V, which is way below what's feasible with any 478 socket CPU that will run on this board. This feature alone helps makes the ST61G4 worthy of a silent tweaker's attention.

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