CSM (Compatibility Support Module)
Also searched as: csm · compatibility support module · legacy boot
What it means
A BIOS option that lets modern firmware boot in an old-fashioned legacy mode for older operating systems and hardware. On a current gaming PC you generally want it off.
More detail
It matters because Secure Boot and some anti-cheats need CSM disabled to work, and flipping it on a Windows install set up the other way can stop the PC booting. If you change it, know that you may need to adjust how the drive boots too. For most modern builds the correct state is off — but change it deliberately, not on a whim.
The Compy Blackbook holds 174 graded entries like this one, judged against your hardware — and every change it does make is reversible, with the receipt to prove it.
See Compy →