With the components defined, we can now take a closer look at how they affect layout and how layout is affected by them. The Asus motherboard below has several strong features and a few drawbacks that will put things into perspective.
A primary layout consideration is the amount of clearance that graphics cards have relative to other devices. The example above puts the uppermost PCIe x16 slot in the second slot position (see the blue slot), providing a small amount of space between the back of a long graphics card and the DIMM latches to ease the replacement of memory with a graphics card installed. Increasing that space could have been accomplished by moving the RAM towards the motherboard's upper edge, shown on the right in this photo, and Asus has more recently released motherboards that have no latches on the lower end, shown on the left side of the DIMM slots above.
The lower PCIe slot on the above board is a different matter. Behind it are four SATA connectors, two of which (the red ones) may be blocked by graphics card coolers on long cards, such as ATI’s Radeon HD 5850 and Nvidia’s GeForce GTX 260. Long cards would further block access to the blue ATA/100 connector, except that it has wisely been turned 90 degrees.
Most current “enthusiast” motherboards have now turned the SATA connectors in the same direction as the ATA connector above, so that it must be plugged in from the front edge. While this allows extra-long expansion cards to be installed into nearly any slot, some traditional case designs have a hard drive cage that blocks access to forward-facing ports. While most “enthusiast” market cases have been redesigned to allow SATA cables to pass around the hard drive cage, case reviews should be able to clear up any doubts.
The above motherboard stands out having slots in all seven slot positions, whereas many alternatives support only five or six cards. Asus accomplished this without crowding the DIMM slots, by putting a PCIe x1 slot above the uppermost x16 slot (see the small white connector next to the blue PCIE x16 slot). Typical PCIe x1 cards are usually short enough to avoid crowding DIMM latches, although the oversized chipset heat sinks of many motherboards further restrict card length.
The top edge is preferred for the ATX12V/EPS12V connector because it allows the cable to be pulled past the CPU cooler without blocking or touching its fan. This design also allows the cable to be pulled up behind the motherboard tray in cases that have the power supply at the bottom, and many manufacturers have redesigned their high-amperage power supplies with longer cables to accommodate this configuration.
The larger 20- or 24-pin ATX/EPS power connector should always be placed at the front edge of modern motherboards to allow easy access in cases that have the power supply at the top or bottom, without blocking the CPU cooler or any expansion slots. Some entry-level motherboards have placed this connector between the CPU socket and rear-panel ports, a design that never gets the stamp of approval from Tom’s Hardware, regardless of the motherboard’s other qualities.
Because Serial ATA (SATA) cables now connect both optical drives and hard drives or solid-state disks, the connectors should be placed near the mid-point of a motherboard’s front edge. The motherboard photographed above was designed for an era when SATA was reserved primarily for hard drives, and instead placed its outdated Ultra ATA connector appropriately for the upper bays of tower cases.
The ideal location for front-panel audio connections is behind the rear-panel audio jacks, to ease cable routing for mid- or top-mounted front panel ports. Because this portion of the board is usually crowded, the area in front of the slots becomes an acceptable location for front-panel USB and IEEE 1394/FireWire connectors. Front-panel connections should never be mounted in the lower rear corner of the board, as many cases use cables that simply won't reach that far. Yet because so many otherwise-exemplary motherboards have inconvenient front-panel connector placement, the final decision of whether or not to use a particular motherboard can be based on a thorough examination of the chosen case.
A final layout consideration is fan connector number and placement. The motherboard pictured above provides a perfect minimum configuration, its CPU fan connector near the DIMM slots, exhaust fan header near the audio ports, intake fan connector in the front lower corner, and another fan connector near the northbridge. Two intake and exhaust fan headers are preferable, and connections for any side and top fans should also be considered. Adapters may be used to connect additional fans directly to the power supply, although this method removes the motherboard’s ability to control fan speed.
Admittedly, we are critical of layout and positioning issues, but our goal is to indicate possible problems, not to eliminate any particular product from further consideration.