Overview

The Framework defines a new firmware model and achieves many advantages ranging from modularity, ease of firmware development even by multiple organizations, to reduced time to market for a product. However, the Framework does not define the runtime interfaces used by traditional operating systems. Thus, the Framework faces the immense challenge of ensuring the functionality of an enormous amount of legacy software.

The designers agree that all existing software must work flawlessly under the Framework. The legacy software requires traditional BIOS runtime services to function. The efforts of making legacy BIOS runtime services available under the Framework result in the birth of the Compatibility Support Module (hereafter referred to as CSM).

The CSM translates the information generated under the EFI environment into the information required by the legacy environment and makes the legacy BIOS services available for booting to the operating system and for use in runtime. The CSM also facilitates EFI to use the traditional Option ROMs. Thus, the CSM empowers a system with the ability to support EFI, legacy BIOS, or both under the Framework.