Nowadays more and more PCs, Tablet PCs and Servers hardware come equipped with UEFI BIOS. Often these boards can be configured in Legacy mode to keep the old features, Especially the PXE- Boot support. But also an increasingly number of devices with UEFI BIOS, do not have a Legacy mode (Especially Tablet PCs).
So they can‘t be administrated via Netboot, which is required for the current opsi environment.
The opsi extension module for UEFI / GPT allows the integration of UEFI devices into the opsi environment.