The first Personal Computer or PC is designed in 1980’s by IBM. This computer has different components and design from previously designed computers. This design is cloned by a lot of manufacturers. This computer boot sequence was like below.

BIOS -> Operating System

BIOS was  the first component that runs when computer starts. BIOS initialization hardware and make some checks and then start operating system resides in disk or network.

UEFI is next generation BIOS which provides a lot of functionalities. New computers are shipped with UEFI.

History

Inter developed Extensible Firmware Interface (EFI) 2005 . And used Windows related data formats.This standard is updated and version as UEFI 2.1 in 2007.

Advantages

UEFI has a lot of advantages over BIOS and other non standard firmware.

• Ability to boot large disks
• CPU-independent architecture
• CPU-independent drivers
• Flexible pre-OS environment
• Modular design
• Backward and forward compability

Services

There are two type of services

• Boot Services: Services provides access to the various devices like bus, block and files services
• Runtime Services provides access to the date, time, NVRAM for the operating system after the boot. CIA has used ExisBootServices for trojan injection

Application

UEFI can load applications an run them accordingly.  The run time flow is operated like below.

Secure Boot

One of the most speculated feature for UEFI is secure boot feature. Because This feature prevents unsigned operating systems to boot. At the time Windows declared that it will prevent unsigned operating systems in preloaded PC’s.

Shell

Shell provides interactive console to get various environment related information. Whit shell firmware information, memory map, modifying boot parameter, partitioning disk can be done.