What is the Difference Between a Quick and Full Format?

What is the Difference Between a Quick and Full Format?

The term formatting is used for different things.
First it is used for low-level formatting of a hard disk. This includes taking the disk and dividing it into small units – the blocks, which can be accessed by the operating system. Nowadays the manufacturers configure the sector size (like 512 bytes or 4096 bytes) and low-level format the disk. Normally the user can’t low-level format a hard disk anymore.
Second, formatting is used for high-level formatting of a hard disk. This means that the operating system is writing a file system structure to the disk. With good old FAT (File Allocation Table) for example, the system would write a boot sector to the first disk sector and an empty FAT to the following sectors. Empty in this case means that all entries in the File Allocation Table are marked as unused.
High-level formatting might include scanning the disk for bad sectors (check if every sector can be read), and it might include writing zeroes to all data sectors on the disk.
When you format a disk, Windows XP does a high level format and it writes a file system structure to the disk. When you say full format, then Windows XP also scans all sectors on the disk for bad sectors (see MSKB 302686). Since Windows Vista, a full format writes zeroes to all data sectors (see MSKB 941961). Accessing each sector on the disk takes much more time than the quick format, which only writes the blocks that contain the file system structure. So normally a quick format is what you want because it is much faster. But there are cases where you might want to do a full format.
1. You might have a disk that you want to destroy or give away. If you just do a quick format, then the file data is still on the disk, only the file system structure (file names and information where the files are stored on the disk) are deleted. With specialized programs someone might try to “undelete” your files – the data is still there, the task of the program is to guess/know which data block belongs to which file.
2. You might not be sure if the hard disk is in a good state. Then a full format is a good idea because it accesses every sector, so if any sector is bad, this will be recognized. With a quick format only a few sectors will be written to. With bad luck you end up with a successful quick format, and when you want to write data to the disk later, it fails. Then you will probably be wishing you had done a full format that would have checked the entire disk right at the beginning. Of course you can always run a ‘chkdsk /r’ later to scan a disk for bad sectors.
You asked about risks and consistency. I wrote about the risks above. Regarding consistency there is no difference. With every format the operating system writes the file system structure, and this structure is the starting point for every file system access. It does not make any difference if unused sectors are zeroed out or filled with random data.

For more information, you might want to take a look at the Wikipedia Article for Formatting.

Windows installation of 7, 8, 8.1, 10 hard disk format. 
      
When you first pop-in your Windows disk, the operating system will prompt these choices for you to choose from. Here are the format options:

• Format the partition by using the NTFS file system (Quick)
• Format the partition by using the FAT file system (Quick)
• Format the partition by using the NTFS file system
• Format the partition by using the FAT file system

When you choose to run a Full format on a volume, files are removed from the volume that you are formatting and the hard disk is scanned for bad sectors. The scan for bad sectors is the reason why the Full format takes twice as long as the Quick format.
If you choose the Quick format option, the format removes files from the partition, but does not scan the disk for bad sectors. This option is best when your hard disk has been previously formatted and you are sure that your hard disk is not damaged nor has bad sectors. This can be a problem later because bad sectors that are not located can cause damage to the hard drive. For example, if data is later installed on this “bad sector”, the data will read errors or as corrupted files.

In simple terms, a Full format will truly scrub through the hard drive from scratch, rebuild all of its file structures, and scans the drive to make sure that everything is on a satisfactory level. On the other hand, what a Quick format does is lay down a blank FAT and directory table without checking for bad sectors.
This is why when you buy a brand-new unformatted hard drive, you cannot give it a Quick format. The drive needs a Full Format because it needs the entire file structures set-up, so the FAT actually has blocks and sectors to track, rather than a chaotic mess. However, like we mention earlier, if your hard drive is already has a clean slate and has no bad sectors, a Quick format will be suitable.
Also, If you installed Windows on a partition that was formatted by using the Quick format option, you can check your hard drive by using the chkdsk /r command after the installation of Windows is completed. In conclusion—don’t be lazy. You already went the distance with the tedious task of reformatting. Select the Full Format and both your computer and you will live in harmony… until the next format.