-Suppose you have a Book. The book has a Table of Contents and pages(your data). In a quick format, basically just delete the table of contents so when the hard drive sees it, it thinks the book is empty so when it starts writing data, it will just ignore your old data which is what is already written and just wright on top of it. However a full format is not just earasing the table of contents of the book, but throwing away the book and getting a brand new book with nothing there and starting new. However there is absolutly no difference between the two for the majority of normal end-users. I am not fully sure but unless you are switching file systems there is no need to do a full format according to people i know.
-And about the hard drive defragmentation, i am not sure but I think its because while its defragmentating and moving files, it needs a temporary place to put all of it, buts it what i think, not sure about it though.
whats the difference between a quick and slow format,what happens to the sectors and clusters durrning slow and quck format.
and when doing disk defragment, why does it require 16% of free space?
Quick format ONLY writes the metadata - the Master File Table, freespace map and directory structure. Full format also zeroes every sector on the disk to ensure it's writable and readable. Any bad sectors found are remapped so that they won't be used.
Defragmenting a disk means moving the files around in order to make them (and the free space) contiguous. You can't move a file unless you've got some free space to move the file into. Imagine a room that's 100% full of tables - there would be no way to move the tables anywhere. You need enough empty space to hold a few tables if you want to be able to rearrange them, kind of the same way you need an empty space in a sliding tile game:
i know that Defragmentation needs empty space, because it have to move the fragment files to an empty space first then to where it belongs for fast access, but what im asking is why 16% not 20% or 10% for example.
I believe the defragmenter analyzes the files it needs to move and decides on the minimum amount of space it needs to do the job in a given number of transfer iterations. I don't think 16% is an absolute limit, because I've had it refuse to defragment with over 20% free space. But you'd have to talk to someone who knows it's algorithms to be sure.
First, Dextermat was right to indicate this has NOTHING to do with "Low-level Format". That procedure is done at the HDD factory. It is very specific to the hardware of the disk device, and it actually creates the magnetic tracks and their boundary markers on the blank media platters, plus establishes a whole bunch of hidden data and resources necessary for the hard drive's own control board to manage its many functions.
What many these days call "Low-level Format" actually means a two-step process necessary on any new empty disk (also can be re-done on used disks) before it can be used by an Operating System. The first is Partition. This writes to specific standard locations at the very start of the disk an MBR (a small machine code piece used to boot from the disk) and the Partition Table, a set of data detailing exactly how the space on this physical device is allocated to one or more Partitions. From then on, each Partition is treated as a separate "drive". The second step (and this one really is done by the OS since its details depend on what OS is using the disk) is Format, done separately for EACH "disk" or Partition. It writes the hidden key data structures at the beginning of the disk used to track the use of disk sectors to files. These include a Root Directory, a table of use of Allocation Units, and some other files I don't understand!
Now, a Quick Format will do that second step - write the key structures - and use the Partition size to tell you the available space and a few other things, but it does NOT look at the rest of the disk. A Full Format, on the other hand, does a complete test of every individual sector of that drive by writing material to it, then reading it back and checking that it is right. Recent versions of Windows conclude this part by writing zeroes specifically to the sectors when they are done. If Windows finds any sectors unreliable, it marks them in the Allocation Unit tracking files so they are never used. Because this is a lot more work, a Full Format takes much longer. We did that recently on a 1.5 TB drive in a fast machine, and Full Format took over 5 hours, versus less than 10 minutes typically for the Quick version.
Most new drives are so reliable there are no faulty sectors for Windows Full Format to find, but it is not impossible. So a Full version is just an extra safety move if you have the time.