The FN25 motherboard is custom designed for this particular chassis. It supports all Socket 939 AMD Athlon 64 processors with a 1GHz Hyper Transport bus and dual channel 184-pin DDR memory modules at 333/400MHz, with capacity for up to 2GB in two memory slots.
The motherboard has the basic version of the NForce 4 MCP chipset, meaning that there is no SATA II support and also no ActiveArmour. However, you still get NVIDIA's firewall and complete PCI-Express support, with the inclusion of a single PCI-Express x1 slot and a PCI-Express x16 slot for your choice of video card.
The PCI-Express slots have been moved to the opposite side of the motherboard than what is typical of previous P-series chassis. That, along with the increased power supply capacity means that you can install video cards with dual-slot cooling solutions, such as ATI's Radeon X850 XT and NVIDIA's GeForce 6800 Ultra.
While on the topic of the power supply, Shuttle have gone for a proprietary solution and lost the standard ATX socket in favour of two smaller sockets that are specifically designed for the motherboard in the SN25P. If you plan to use the motherboard in another chassis or as part of a system modification, you'll have to use the power supply that is included as well.
The MCP is actively cooled with a small 40mm fan that blows air across a substantial aluminium heatsink. Rather than blowing air directly down on the chipset, it blows air across the heatsink in a more unconventional manner. There is a single ATA133 port, four SATA ports, which are rated at 150Mb/s and support NVIDIA RAID (0, 1, 0+1 and JBOD), and a single floppy connector. The chassis has space for one 5.25" drive and three 3.5" devices.
8-channel audio is provided by the VIA Envy24PT controller, which can deliver up to 24 bit/96KHz audio resolution and sampling as well as support for Dolby and DTS decoding. Gigabit LAN is provided by the Marvell PHY Gigabit Ethernet controller. A 'Physical Layer' controller chip is directly wired to the NForce4 MCP to allow you to gain the full throughput of the Ethernet controller. Firewire is provided by the common VIA VT6307 controller chip, but only two out of the maximum three supported ports are used: one is located on the front panel, and the other is located on the back I/O panel.
Finally, the designers of the chassis have paid special attention to the cable routing: everything has its place and is routed to keep it everything as tidy as possible. A couple of SATA and power leads are pre-plugged in and routed around the chassis ready for you to install your hard disk drives. This is another clever and necessary thing - cable routing is requires careful consideration for every self system builder out there, and even more so with such a small chassis, with the cable pre-routed and designed specifically for the case it makes everything a damn sight easier.