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Memory And Expansion Card Slots

How To Choose A Motherboard: A Guide For Beginners
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Memory technology support and configuration limits are normally thought to be tied to on-die controllers, but a motherboard's slot configuration can further limit your choices. For example, several microATX and smaller motherboards expose only two memory slots. Certainly, it's best to have at least four DIMM slots on a dual-channel motherboard or eight on a quad-channel platform, whenever the space for these slots exists.

All current motherboards support PCI Express 3.0 graphics cards (8 GT/s), though chipsets for AMD’s Socket AM3+ are limited to PCIe 2.0 transfer rates (5 GT/s). The transfer mode for platforms with CPU-based PCIe controllers is also limited by that component, so that putting a previous-generation Socket FM2 processor in a current-generation FM2+ motherboard will result in the slower transfer rate. Intel faced the same issue in its Sandy Bridge (PCIe 2.0) to Ivy Bridge (PCIe 3.0) transition two years ago, since both of those processors dropped intro the same interface.

PCIe x16, represented by the long slot in the image below, is primarily used for graphics cards. Thanks to standardization, it’s also compatible with non-graphics cards all the way down to PCIe x1. And it’s compatible with different generations, so that a PCIe 3.0 slot can host a PCIe 2.0 or 1.1 card without issue.

The two smaller slots in the above image correspond to PCI Express x8 and x4. They're suited for high-bandwidth devices like RAID controllers with eight or more drives and multi-connection GbE network cards. Notice also that they're open-ended. There's no plastic capping the back, which allows longer cards to fit in shorter slots if needed. Just remember that not all slots are open-ended. The feature is not well-documented, and you may need to look at photos of the actual product to determine if your longer card really fits into that shorter slot. And as long as you’re looking at pictures, you should also keep an eye out for other obstructions that could interfere with the use of an open end (such as the white heat sink pin, below).

The marketing force of CrossFire and SLI pushes motherboard manufacturers to put “graphics slots” in as many places as they can, even using physical x16 connectors wherever an enthusiast-class board has an electrical x4 or x8 link. As a result, x8-appearing connectors have become a rarity, even as x8 interfaces are incredibly common. The above motherboard also shows one example of a x8 slot that only appears to be x16; you can barely see the missing pins in the last slot.

Due to the limited number of pathways found on mid-priced platforms, many enthusiast-class motherboards can’t enable all of their slots simultaneously. This is a bad habit we try to call out whenever we see it. After all, it could be a huge hindrance to anyone with expansion plans for their whole board. It's most often a problem for the bottom faux-x16 slots of ATX-sized LGA 1150- and Socket AM2+-based motherboards, as well as earlier versions of those processor interfaces. These slots are usually wired to four lanes at most, sharing up to three lanes with x1 slots and/or on-board devices. Unless the manufacturer adds an expensive switch, slots or devices have to be disabled to make others operational. Because this is such a large problem for a few buyers, we list slot sharing in the Page 1 motherboard features table of our reviews. Motherboard manufacturers also list these limitations within the technical specifications sheet of each motherboard’s product page.

Added-in Controllers

Adding to the vast array of features controlled by the southbridge are third-party devices like 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, an increased number of chipset-integrated USB 3.0 ports, and decreased popularity of FireWire devices. Add-in controllers usually employ PCIe x1 connections, using a logical "slot" where no room exists on the motherboard for a physical slot.

It may seem counter-intuitive to disable any device that increases motherboard cost, but doing so can reduce boot time. For example, the separate BIOS of unused add-in SATA controllers will often flash a "no drives found" error message just before the OS splash screen appears.

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    Rugnir_Viking , 1 October 2014 09:22
    This seems to be a very long article about a fairly short topic.
    Does the mobo have enough pci-e x16 slots
    Does the mobo have the right chipset for the cpu
    Does the mobo have enough ram sockets

    Enough for your 'beginner'

    [EDIT]
    I suppose perhaps you might need to ensure form factor is correct.
  • 0 Hide
    RaduZ , 5 October 2014 21:56
    Personaly the first thing I check on a MB i want to buy is the power delivery. What caps is it useing, how many real phases does it have and things like that.
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