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Opening 'er up
Enough with the outside, let's slide off the SN25P's aluminum shell and have a peek at what lies under the hood.

A loaded SN25P from the left...

And the right

With support for external 5.25" and 3.5" drives and two internal 3.5" hard drives, the SN25P's internals are surprisingly expansive for a small form factor system. Hard drives reside side by side along the top of the system and slide into place on a pair of very slick tool-free, snap-on rails.

The snap-on rails make mounting drives in the SN25P easier than in most full ATX systems, which is pretty remarkable. Shuttle also includes a handful of rubber bumpers to dampen vibrations between hard drives and the case's aluminum shell. It's a good idea in theory, but the stiff rubber bumpers are too tall for the limited clearance between hard drives and the system's outer skin. You can force the shell back on with the bumpers installed, but that flexes the hard drive rails to a point that I'm not entirely comfortable with. Thankfully, it's easy to trim the bumpers down to a more reasonable height.

Like the hard drive rails, the SN25P's external drive cage is a tool-free affair. External 5.25" and 3.5" drives get rails of their own, and the entire drive snaps into place with nary a screwdriver in sight. With the drive cage removed, we can take a closer look at the rest of the system's internals.

The SN25P's PCI Express x16 slot is mounted on the outside edge of the system, leaving just enough room for double-wide graphics cards like ATI's Radeon X850 XT and NVIDIA's GeForce 6800 Ultra. Such cards will block the system's PCI-E x1 slot, but until PCI Express peripherals become more prevalent, it won't be missed.

Around the other side of the system, users have easy access to the SN25P's DIMM slots.

The FN25 motherboard's layout is as tight as one would expect from a small form factor system. Notice that the DIMM slots run down the middle of the board rather than along its top edge, presumably to maintain closer proximity to the Athlon 64's on-die memory controller. Also note the use of an active chipset cooler for the nForce4, which is developing a reputation for running a little warmer than most chipsets.

Shuttle hides the FN25 motherboard's most interesting feature up in the top corner of the board. Here, we find VIA's Envy24PT audio controller, VT1617A codec, and a Wolfson WM8728 DAC. With support for 24-bit audio at sampling rates up to 96kHz, the Envy24PT hints at high-definition audio, but it's not quite that easy. With analog output, codec and DAC sampling rates and resolutions also come into play, and that's where the SN25P's implementation falls a little short. The Envy24's first six output channels are routed through the VT1617A codec, which only supports resolutions up to 20 bits and sampling rates up to 96kHz. The Wolfson DAC supports 24-bit/192kHz audio, but in an eight-channel configuration, it only handles channels seven and eight.

It would be wasteful just to use the high-end Wolfson DAC for channels seven and eight, but VIA's Envy24PT drivers actually allow users to route two-channel stereo audio through the WM8728. This pipes stereo output through the SN25P's rear 7/8 audio output, potentially offering superior fidelity to the VT1617A. At the very least, the driver switch allows users to enjoy two-channel 24-bit/96kHz audio output through analog speakers or headphones without having to worry about downsampling sapping fidelity.