Content

Overview

With the help of CSM (Compatibility Support Module) in Hungarian (compatibility support module) modern UEFI motherboards are backward compatible with the old BIOS system motherboards, which boot the MBR performed from hard disks with partitions. So, thanks to the CSM module, UEFI motherboards can also boot operating systems from these older drives. In this case, the boot is performed in the same way as on older BIOS-based systems: relying on the contents of the boot sector, the partition table is ignored.

BIOS boot from MBR partitions is also called BIOS-MBR, regardless of whether it was performed on a UEFI or an old BIOS-based system. In addition, it is possible to boot legacy BIOS based systems GPT disks, which is called BIOS-GPT.

CSM allows you to use legacy operating systems and some optional ROMs that do not support UEFI. In addition to its services, UEFI SMM also provides the required legacy system management mode (SMM) functionality, called CompatibilitySMM. It is optional and highly chipset and platform specific. An example of such old SMM features is the provision of legacy USB support for the keyboard and mouse by emulating their classic PS / 2 predecessors.

In November 2017, Intel announced that it plans to phase out CSM support by 2020.