BIOS and UEFI
Basic Input / Output System (BIOS)
The GRUB is used to manage and boot up linux operating systems on computers that use the BIOS system.
These are typically older computers or those that did not come with Windows 8 pre-installed. It is worthwhile noting that the UEFI can be disabled on many systems to run using the BIOS instead; this is known as running in Legacy Mode.
Computers sold prior to the release and pre-installation of Windows 8 - which introduced UEFI - will therefore use the GRUB.
- Easily customize GRUB2 with the Grub-Customizer GUI tool.
Unified Extensible Firmware Interface (UEFI)
UEFI was introduced with Windows 8 as a replacement / upgrade to the BIOS system. One example of this upgrade is that it allows for computers to use hard-disks larger than 2 Terrabytes (2,000 Gigabytes). Unfortunately, UEFI was also secretly manipulated by Microsoft in tandem with certain hardware manufacturers to prevent - or at least make it very difficult - to remove and replace Windows 8 with another operating system.
For example, other - competing - operating systems must currently seek permission to be "authorised" by Microsoft in order to be installed on UEFI systems. This "feature" can be disabled, albeit after warnings about "security", as well as the need to enter in a code. Even then, the UEFI will likely be configured to ignore any other installed systems and either boot into Windows 8 anyway.
AS UEFI systems still contain the old BIOS system, UEFI can be disabled or even removed completely to run in Legacy Mode. The author did so with a laptop using a 1 Terrabyte (TB) hard-disk, which the BIOS can handle.