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Memory type and configuration limits are normally thought to be those of the memory controller, but motherboard's slot configuration can further limit choices. For example, several Micro ATX and smaller motherboards provide only two memory slots, both wired to a single memory channel, making a dual-channel capable memory controller pointless. Certainly, it's best to have at least four DIMM slots, and workstation boards often feature eight or more.
AGP and AGP Pro slots are limited to older technology graphics cards, which have lost their value compared to PCI Express parts. Owners of reasonably powerful AGP graphics cards may still wish to choose AGP-supporting motherboards as replacement products, however. PCI supports the widest variety of expansion cards and will remain dominant for several years, while PCI Express replacement products slowly evolve. Because personal systems often change roles during their useful lives, it's a good idea to have at least one more PCI slot than the original system plan requires. PCI-X is a server/workstation card standard based on PCI, but extended to 64 bits at clock rates up to four-times as high. This should never be confused with "PCX", an acronym Nvidia uses in place of PCI Express. Express (PCIe) x16 slots are normally dedicated to graphics cards, but a second slot can also be used for non-graphics purposes. Flexible configuration allows wider cards to operate on narrower pathways and vice versa, so that previous generation chipsets split the 16 pathways normally associated with a single x16 card across two x16 slots with x8 pathways. Newer high-end ATI and Nvidia chipsets support the additional pathways needed for two actual x16 slots.
PCI Express x8 and x4 slots are suited for high-bandwidth devices such as RAID controllers with eight or more drives and multi-connection gigabit network cards. These PCIe slots will eventually displace PCI-X in workstations while making workstation-class products an option for personal systems.
PCI Express x1 slots are designed to replace the most familiar PCI slots, and offer twice the bandwidth available in both directions, and are perfect for medium bandwidth devices such as single-connection gigabit network cards, two-drive ATA controller cards and TV tuner cards.
PCI Express slots with an open end, such as found on several MSI motherboards, allow the use of longer cards in shorter slots, such as a x8 card in a x4 slot. The Gigabyte GA-M59SLI goes one step further by putting an x16connector on its x8 slot.
Any of these slot types can prove equally valuable in a new build, making card selection an important first step towards determining motherboard requirements.
Adding to the vast array of features controlled by the Southbridge are third-party devices such as secondary ATA controllers (for more drive support), IEEE1394/FireWire and/or SCSI controllers. Several factors have pushed these out of the mainstream and into smaller high-end markets, such as better-featured on-chipset ATA controllers, decreased popularity of Firewire devices and the extinction of SCSI PC peripherals.
Add-in controllers usually employ PCI connections, using a logical "slot" where no room exists on the motherboard for a physical slot. With only seven physical slot positions available to a full-sized ATX or BTX motherboard, a typical chipset supporting four PCI Express devices plus six PCI slots will have several unused connections, which can be routed directly to onboard PCI devices.
It may seem counter-intuitive to disable any device that increases motherboard cost, but doing so can reduce boot time. For example, add-in ATA 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.