For most computers, the standard used for accessing hard disk data is based on old BIOS conventions that were introduced with the f rst personal computers. When a computer is first started, its BIOS firmware is responsible for initializing the computer. The computer must find and load the operating system after required boot hardware components are tested and initialized by the BIOS's Power On Self Test (POST) routine. The BIOS design introduced the concept of a Master Boot Record (MBR) enabled disk.

• The MBR disk partition style defines where the BIOS examines the disk drive to determine where data is stored on the disk and the types of data it contains. MBR disk technology is still common today because the startup routines for most x86 32-bit and x64 64-bit computers are based on it.
• The computer's BIOS looks to the first hard disk it finds and loads a small program from the very first block of space on the disk. That small block of data, or sector, is called the boot sector. The boot sector is the first part of the Master Boot Record (MBR). The boot sector code is typically written when the operating system is first loaded on the computer and the MBR is created.
• The MBR also includes a data table that identifies how sections, or partitions, of space on the disk are used to store files. MBR disk technology is limited to organizing partitions on a single logical drive up to 2 terabytes (TB). If the drive is larger than 2 TB, the space beyond 2 TB is visible in Windows 7 but is not able to be used for any purpose.