The boardIntel 5-series mATX boards make implicit sense because the CPU architecture is such that there is no need for an IOH (Input/Output Hub), as per X58. The IOH's main task is to facilitate the routing of PCI-Express lanes, 36 in total, to/from the CPU via a high-speed QPI link. The IOH is also connected to the southbridge via a regular DMI interconnect.
LGA1,156 chips differ from their LGA1,366 brethren by integrating the PCI-Express lanes directly from the CPU. That, then, removes the need for an IOH and QPI link to the processor but reduces the total number of lanes to 16. The chipset, P55 for example, connects to the CPU via DMI, just as the X58's IOH does. In effect, the integration on LGA1156 (Lynnfield) is such that it integrates a complete northbridge to the execution cores. Say goodbye to the IOH.
The southbridge-only 'chipset' frees up a generous amount of board real estate, to the extent that the Gigabyte mATX isn't cluttered.
The GA-P55M-UD4 features four DIMM slots for dual-channel DDR3, two x16 PCIe mechanical slots that can be broken down to two x8 for multi-GPU usage.
CPU layout is pretty good and it's easy to install a reference cooling without fouling the small-ish heatsinks. The 8-pin power connector is nicely tucked away, positioned just underneath where most PSUs will be located.
A couple of four-pin and two three-pin header are good for cooling, too.
It also features some of Gigabyte's usual technology in the form of dual BIOSes and a PCB with 2oz copper.
The main 24-pin connector and PATA port are also located at the edge of the board, which makes sense.
Our sample board is equipped with a Marvell chip (88ESE9123) for SATA 6Gbps operation. However, Gigabyte has confirmed that retail 'UD4 boards will have the older JMicron JMB363 (3Gbps) controller.
Power, reset and clear-CMOS buttons are nice to see on a mATX board, and the southbridge's heatsink is low-profile enough not to interfere with longer graphics cards, but the reset and clear-CMOS might just be obstructed.
The two x16 slots run off the CPU and provide both CrossFire and SLI multi-GPU compatibility. The shorter x4 slot is pulled from the P55 chipset.
The floppy port is awkwardly placed at the bottom of the board.
Gigabyte sees fit to include 10 USB ports on the back, of which one also serve as a board-powered eSATA port. PS/2, analogue audio (Realtek ALC889A), FireWire400 (TI TSB432AB23), both coaxial and optical S/PDIF-out, and Gigabit Ethernet (Realtek 811Dround off an impressive backplane.
What we don't yet know is the price, but here's hoping for around £100. Pair one of these up with an upcoming Core i5 750 and 4GB of DDR3 and you should have decent change from £300.