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In this section, it is essential to differentiate between the FAT file system and the file allocation table (FAT).įAT is the file system used by DOS operating systems (DOS and Windows 95, as well as Windows NT and OS/2, which support it). In other words, your hard drive is useless without it, making it a favourite target for viruses. This sector is, therefore, the most important on the hard drive and is also used by the BIOS setup to recognize the hard drive. This disk sector also contains all the information concerning the hard drive (i.e., manufacturer, serial number, number of bytes per sector, number of sectors per cluster, number of sectors, etc.).

It contains the primary partition table and the code, called the bootloader, which, when loaded into memory, will allow the system to boot up.Īfter it is loaded into memory, this program will determine which system partition to boot and will start the program (called the bootstrap), which will start up the operating system present on that partition. What is a “master boot record”? The boot sector (called the Master Boot Record or MBR) is the first sector of a hard drive (cylinder 0, head 0, sector 1). Here is an example of where the disk contains one primary partition and one extended partition made up of three logical drives:įor DOS systems (DOS, Windows 9x), only the primary partition is bootable and is, therefore, the only one on which the operating system can be started. In the extended partition, the user can create logical drives (i.e., "simulate" several smaller-sized hard drives). A disk may contain up to four primary partitions (only one can be active), three primary, and one extended partition. Three types of partitions exist: primary, extended, and logical. That is unless you want to create several partitions to have several drives on which data is kept separately. A single partition of the full disk size is sufficient if you use just one operating system. Therefore, logically there will be at least as many partitions as operating systems using different file systems. It can be used, for example, to install different operating systems that do not use the same file system. It involves creating areas on the disk where data will not be mixed. The partitioning of a hard drive occurs after the drive has been physically formatted but before it is logically formatted.