3.Data storage region of hard disk

3.Data storage region of hard disk
In command to know hard disk better, we must have a simple understanding of hard disk
construction. (NTFS uses different file management technology with FAT16 and the FAT32 file
system, here we only introduce FAT16 and FAT32) The hard disk data may divide into 5 parts
approximately according to its different characteristics and functions: MBR area, DBR area, FAT
area, DIR area and DATA area. Among them, MBR is founded by the partition software, while
DBR area, FAT area, DIR area and DATA area are founded by high-level format procedure. When
file system writes in data, it just rewrites corresponding FAT area, DIR area and DATA area. Also
it is the result which these 5 regions affect together. Only by this way, hard disk can be managed
methodically. Here are some introductions to the 5 regions.
MBR:
The first physical sector (cylinder 0, head 0, sector 1) of the first hard drive in the system (the first
hard drive with the BIOS device number 0x80); each hard drive contains an MBR, but not every
BIOS can start the corresponding operation system from every hard drive. When booting from the
hard drive, the BIOS or a special Firmware loads the contents of the MBR to a fixed address in the
memory and allows it to take control. This code then loads either the operation system from a
bootable hard drive partition, or from a complex boot loader, such as LILO.
Short for DOS Boot Record it is the sector at cylinder 0, column 1, and sector 1 of a hard disk.
DBR is the first sector that the operation system visits. It contains a boot program and a BPB
(BIOS Parameter Block). The main task of the boot program is to determine whether the first two
files in root directory of this partition are the boot files of operation system, when MBR hands
over the system mastery to it. Take an example of DOS, i.e. IO.SYS and MSDOS.SYS. DOS of
low edition requests that these two files are the first two files, and located at the section start of the
root directory, covering the first two directory items (the high edition does not have this
requirement.). Moreover, Windows and DOS are families; therefore, Windows follows the same
management manner, except for the filenames. If it does exist, then reads IO.SYS in the memory,
and hands over mastery to IO.SYS. BPB parameter block records the start sector, ending sector,
file storage form, descriptor of hard disk media, size of root directory, number of FAT and size of
allocated cell.