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Where are my SSDs and how can I expand them?

Modern motherboards sometimes offer up to five M.2 slots on the front. Smaller ITX motherboards may also feature M.2 slots on the back of the motherboard.

In our desktop PCs, the factory-installed SSDs are usually positioned so that they are easily accessible. Depending on the motherboard and chassis, additional slots might be behind covers or shrouds. And often they can only be accessed by remove the system's graphics card first. See also:

  • Can I upgrade the PC myself without losing the warranty?

Individual SSD slots may share PCI Express lanes with the graphics card. If such a slot is occupied, the GPU's bandwidth may be reduced and graphics performance may drop noticeably.

The user manual for the installed motherboard will specify exactly which slots are affected by this GPU bandwidth sharing.

Example:

mainboard-ssd-slot-pcie-lane-sharing-example_en.png

In this example from an ASUS mainboard, the motherboard has five M.2 SSD slots – the two slots marked in red in the middle share the PCIe lanes with the GPU.

This is described in the original manual with the following wording:

mainboard-ssd-slot-pcie-lane-sharing-user-manual-example_en.png

Such slots should only be used for upgrades if the implications are known and acceptable for the system in question.

In the example above, the last three sentences are crucial:

When both M.2_2 and M.2_3 are enabled, PCIEX16_1 will run in x8 mode and PCIEX16_2 will be disabled.
When M.2_2 is enabled, but M.2_3 is not in use, PCIEX16_1 will run in x8 mode and PCIEX16_2 will be disabled.
When M.2_3 is enabled, but M.2_2 is not in use, PCIEX16_1 will run in x8 mode and PCIEX16_2 will run in x4 mode.

"Enabled" here essentially means "in use". The designations "PCIEX16_1" and "PCIEX16_2" refer to the two large PCI Express slots. Of these, #1 is usually used for the graphics card, whilst #2 is available for other expansion cards.

Tip: As an alternative to the M.2 SSD slots, the SATA slots on the motherboard are also a good option; these can be fitted with 2.5-inch SSDs or standard hard drives. With these slots, there is no risk of lane sharing with the GPU.