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Memory And Expansion Card Slots

Best Of Tom’s Hardware: Beginner’s Guide To Motherboard Selection

Memory type and configuration limits are normally thought to be tied to the memory controller, but a motherboard's slot configuration can further limit choices. For example, several microATX and smaller motherboards provide only two memory slots. Certainly, it's best to have at least four DIMM slots on a dual-channel motherboard or six on a triple-channel board, whenever the space for these modules exists.

All current motherboards support PCIe 2.0 graphics (5.0 GT/s), although a few older models that some vendors offer are limited to PCIe 1.1 (2.5 GT/s). There are few compatibility issues between PCIe 2.0 and 1.1 motherboards and graphics cards, although if different generations of parts are to be used, it is best to confirm compatibility by checking with our knowledgeable forum members.

While many non-graphics expansion cards, such as TV tuners and RAID controllers, now use the PCIe interface, several items have not yet been updated. Careful planning is required to make sure newer motherboards support all of your required legacy devices, while it's also a good idea to have at least one more PCIe slot than the original system plan requires.

PCIe x8 and x4 slots are suited for high-bandwidth devices, such as RAID controllers with eight or more ports and multi-connection gigabit network cards. Most consumer boards lack a physical x8 slot, although many have four or eight pathways in an x16 slot. Remember that any secondary x16 slot can also host x8, x4, and x1 cards if required.

PCIe slots with an open end at the front allow the use of longer cards in shorter slots, such as an x8 card in an x4 slot, as long as nothing else blocks the card from being inserted. Gigabyte’s GA-EX58-Extreme is a great example of a motherboard with an open-ended x4 slot that might have been able to support an x8 card, but instead has another obstruction (the white heat sink pin) that prevents anything longer than an x4 card from fitting.

Any of these slot types can prove equally valuable in a new build depending on your unique expansion card requirements.

Added-in Controllers

Adding to the vast array of features controlled by the southbridge are third-party devices, such as secondary network, SATA/eSATA, USB 3.0, and/or IEEE 1394/FireWire controllers. Several factors have pushed these out of the mainstream and into smaller high-end markets, such as improved SATA features, unavailability of USB 3.0 during chipset development, and decreased popularity of FireWire devices.

Add-in controllers usually employ PCI or PCIe x1 connections, using a logical "slot" where no room exists on the motherboard for a physical slot. With only seven physical slot positions available for a full-sized ATX build, a typical chipset supporting six PCIe x1 devices plus five PCI slots will have several unused connections, which can be routed directly to onboard  devices.

It may seem counterintuitive to disable any device that increases motherboard cost, but doing so can reduce boot time. For example, add-in SATA controllers have their own BIOS, but users with only a few drives will likely not have any of them connected to the add-in controller. Disabling the unused hardware will eliminate the time needed for its BIOS to run a drive check and get rid of the unnecessary "no drives found" message.

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