mainboard and boot devices are initialized in DXE and BDS. BDS – Boot Device Select BDS is a part of the DXE. In this stage, boot devices are initialized, UEFI drivers or Option ROMs of PCI devices are executed according to system configuration, and boot options are processed. TSL – Transient System Load This is the stage between boot device selection and hand-off to the OS. At this point one may enter UEFI shell, or execute an UEFI application such as the OS boot loader. RT – Runtime The UEFI hands off to the operating system (OS) after is executed. A UEFI compatible OS is now responsible for exiting boot services triggering the firmware to unload all no longer needed code and data, leaving only runtime services code/data, e.g. SMM and ACPI. A typical modern OS will prefer to use its own programs (such as kernel drivers) to control hardware devices. When a legacy OS is used, CSM will handle this call ensuring the system is compatible with legacy BIOS expectations. Usage Implementations Intel's implementation of EFI is the Intel Platform Innovation Framework, codenamed Tiano. Tiano runs on Intel's XScale, Itanium, x86-32 and x86-64 processors, and is proprietary software, although a portion of the code has been released under the BSD license or Eclipse Public License (EPL) as TianoCore EDK II. TianoCore can be used as a payload for coreboot. Phoenix Technologies' implementation of UEFI is branded as SecureCore Technology (SCT). American Megatrends offers its own UEFI firmware implementation known as Aptio, while Insyde Software offers InsydeH2O. In December 2018, Microsoft released an open source version of its TianoCore EDK2-based UEFI implementation from the Surface line, Project Mu. An implementation of the UEFI API was introduced into the Universal Boot Loader (Das U-Boot) in 2017. On the ARMv8 architecture Linux distributions use the U-Boot UEFI implementation in conjunction with GNU GRUB for booting (e.g. SUSE Linux), the same holds true for OpenBSD. For booting from iSCSI iPXE can be used as a UEFI application loaded by U-Boot. Platforms Intel's first Itanium workstations and servers, released in 2000, implemented EFI 1.02. Hewlett-Packard's first Itanium 2 systems, released in 2002, implemented EFI 1.10; they were able to boot Windows, Linux, FreeBSD and HP-UX; OpenVMS added UEFI capability in June 2003. In January 2006, Apple Inc. shipped its first Intel-based Macintosh computers. These systems used EFI instead of Open Firmware, which had been