Technical Section:
Types Of Operating Systems:
The most common operating systems are MSDOS, DRDOS, PCDOS, Caldera DOS, Win95/98/Me, WinNT/2000/XP, UNIX, LINUX, Novel NetWare, Mac and OS2.
Microsoft Inc has DOS, Win95/98/Me, WinNT/2000/XP products. These are based on four types of file structures. They are FAT12, FAT16, FAT32 and NTFS ( new technology file system ).
A study of partition and logical structure of disk ( FAT and NTFS ):
The outer most track called the track 0 contains the system area of the disk. The system area of the disk is the interface between the operating system and the data on the disk.
It consists of the Partition Table, Boot Sector, File Allocation Tables and Directory Structure. The 0 track has the first physical sector (0 sector) which is the Partition Table. The first logical sector is the boot sector of the disk. After these, start the File Allocation Tables.
There are two identical copies of the FAT. After both the FAT, the directory starts. The data area starts after the Root directory structure. In case of FAT 32, the directory area resides in the data area.
Below are two tables defining the logical structure of the disk.
For FAT 16 Disk.
|
Partition 1 |
Spl. Hidden Sec. |
Boot Sec. |
FAT 1 |
FAT 2 |
Root Directory |
Data Area |
Cylinder
Head
Sector |
0
0
1 |
63 |
0
1
1 |
0
1
2 |
Starts after all the sec. of FAT 1. |
Starts after all the sec. of FAT 2. |
Starts after all the sec. of directory area. |
|
Partition 2 |
|
|
|
|
|
|
Cylinder
Head
Sector |
261
0
1 |
63 |
261
1
1 |
261
1
2 |
Starts after all the sec. of FAT 1. |
Starts after all the sec. of FAT 2. |
Starts after all the sec. of directory area. |
Note 1: Reserve Sector in case of FAT 16 is 1 Because FAT 1 starts from the next sector after the Boot Sector.
Note 2: The Sector Per FAT (SPF) is the number of sectors occupied by each FAT. This value is written in BOOT SECTOR.
For FAT32 Disk.
|
Partition 1 |
Spl. Hidden Sec. |
Boot Sec. |
FAT 1 |
FAT 2 |
Root Directory |
Data Area |
Cylinder
Head
Sector |
0
0
1 |
63 |
0
1
1 |
0
1
33 |
Starts after all the sec. of FAT 1. |
Resides in data area. Normally at cluster number 2. |
Starts after all the sec. of directory area. |
|
Partition 2 |
|
|
|
|
|
|
Cylinder
Head
Sector |
261
0
1 |
63 |
261
1
1 |
261
1
33 |
Starts after all the sec. of FAT 1. |
|
Starts after all the sec. of directory area. |
Note: Reserve Sector in case of FAT 32 is 32 Because FAT 1 starts after 32 sectors from the Boot Sector.
For NTFS Disk:
|
Partition 1 |
Spl. Hidden Sec. |
Boot Sec. |
MFT
Master file table |
MFT Mirror |
Root Directory |
Data Area |
Cylinder
Head
Sector |
0
0
1 |
63 |
0
1
1 |
Anywhere |
Anywhere |
Within MFT |
Small files are within MFT. Larger files are assigned locations outside MFT |
The partition table is located in the first physical sector (0 cyl, 0 head, 1 sector) of the hard disk. It contains the partitioning information of the disk and number sectors contained in each partition. There can be a maximum of 4 logical partitions in the FAT 16 hard disk of maximum 2.1 GB capacity. In case of FAT 32, there can be many more depending on the capacity of the disk. The number of sectors between the partition sector and boot sector is called special hidden sectors (Usually 63).
