Why FAT (File Allocation Table) was come into picture?

        The FAT stands for File Allocation Table. It comes into the picture only for the following reasons. To access a file in floppy disk or hard disk drive (HDD), we need a particular address of that file. For each file the address is different. It not possible that, two files having same address. The files are stored in the tracks and sectors of the disk drive. So it is necessary to assign each memory space a different address. Now think in a traditional way to assign address to each sector. If the sector size is 2 byte and let assume that the address size is 2 byte. Then we need 2 GB to addressing 2 GB space. That’s why the FAT has come into picture. To avoid this problem the FAT combine a bunch of sector and name it as cluster. The cluster size may be 512byte (for floppy), 2k, 4k, 8k, and 32k ….or more than that, depending on the drive space. Now most of the systems are using FAT32.

  The default cluster size of FAT32 is 4k for a drive less than 8 GB. Similarly the default cluster size for less than 60 GB is 8K, for less than 2TB is 16K and for greater than 2TR the cluster size is 32K.

You can get this screen and also able to know about the file system used by the drive by clicking on the property of the drive.

Problem related with cluster size    

  Let the cluster size be 8K. But our file size is 1k. To store the file 1k we need 1 cluster and i.e.8K. So there is wastage of 7K.We can’t store two or more files in one cluster, because it is necessary that every file has got a unique address. Similarly if you have a file having size 9K then it requires 2 clusters that mean 16K. You see this in your computer, if your computer is having FAT32. Just follow the following steps.

Steps

First select a drive which is more than 8.2GB.

Then create a notepad file having 1 character. Save it in any name.

After that check the file size, it will be like this.

Size = 1byte

Size of disk =8K.

If you do the same thing you will do in less then 8GB drive then the file property will show you like

Size = 1 byte

Size = 4K.

     This is a one major draw back of having big cluster size, But big cluster size are used to store MP3, movie file or a file big size. Remember one thing if you storing a file having less then store it in less than 8GB drive.

 If you want to know more related to this, then read file structure.