A disk is divided into circular tracks, also called cylinders.
Each track is subdivided into sectors, also called blocks.
The first sector of a hard disk contains the Master Boot Record (MBR), a table detailing the start and finish sectors of each partition on that disk.
It also contains the master boot code. This program is executed by the BIOS and it proceeds to load and run the volume boot code (see below).
The FORMAT /MBR (MS-DOS, Windows 9x) or
FIXMBR (2000 & XP Recovery Console) commands may be used to
over-write damaged MBR boot code.
The term volume is used to describe a partition, floppy disk or a Zip disk.
The first sector of a volume is its boot sector (or boot block). The boot sector contains a disk parameter block that describes the volume name.
The majority of the disk is divided into groups of one or more sector, called clusters. The cluster size is also recorded in the boot sector.
It also contains the volume boot code. When this program is executed it proceeds to load and run the Disk Operating System (DOS).
FIXBOOT (2000 & XP Recovery Console) will repair a damaged VBR.
The root directory is a list of files and folders on the disk. Each item has a name, date, attributes and the number of the cluster where it starts.
The FAT is a list of cluster numbers. For a given cluster number the FAT gives the number of that file's next cluster.
Floppy disks use a 12-bit cluster number (FAT12). MS-DOS and early Windows 95 disks use a 16-bit cluster number (FAT or FAT16) but this limits a partition to 65,536 clusters. As disks got larger this caused clusters to become very large, wasting a great deal of disk space. For this reason 32-bit cluster numbers (FAT32) were introduced with Windows 95B.
The volume boot code expects to find IO.SYS listed as the first entry in the root directory and the file itself must occupy the first cluster on the disk. The remainder of the file can occupy any other clusters as required.
This file is usually hidden.
In MS-DOS this file originally contained the majority of the DOS program. Since Windows, this file contains some data but is largely redundant.
This file is usually hidden.
This program provides a command-line interface which allows users to type
commands such as DIR, COPY and
FORMAT. It displays the "DOS prompt", which often appears
as A> or C>.
The command FORMAT /S will format a disk and copy these
three system files from the current system disk to another disk. If you
wish to copy the system files without formatting, use the SYS
command.
This file contains device drivers for specific hardware (such as CD-ROMs).
This is a device driver that allows MS-DOS to access extended memory (that is, memory above the 1MB limit imposed on early PCs).
Batch files contain a list of instructions that are to be executed in order. This particular batch file is always executed after booting has completed.
Microsoft CD Extensions (MSCDEX) is a program that allows MS-DOS to mount a CD-ROM as a drive letter.