You regain fragments of wasted space on your hard drive and you reallocate that space for future data stroage use.
It would'nt take forever but yes, normally the bigger your hard drive is, the longer it takes to defrag. It also depends on how bad the hard drive is in need of the defrag.
No! In fact, it's best that you're NOT online while doing a defrag. Anytime defrag hits a part of a hard drive where the information is changing, defrag restarts doing that portion of the drive. While on the Internet, your PC is constantly sending and receiving files and changing what's on the hard drive. Your defrag will take a lot longer.
Do a Defrag. and a Disc clean-up
Defrag
You get viruses and it starts to run slow so defrag it.
Check disc and defrag
1 . Mac machines which comes with HDD requires defragmentation. SSD's no need. 2 . You don't need to regularly defrag a Mac's hard drive, OS X has HFS+ file ,which automatically defrag files of certain size. 3. Download Stellar Drive Defrag 4.. Install it and scan whole Mac, it will take some time and defrag your Mac properly.
Not if you have a good reliable automatic defragger that runs in the background. Once you set it to defrag automatically you really never need to bother about defrag.
When you defragment your computer, it places all kinds of clustered files into a more organized form, taking less time to find them. Be careful not to defrag more than once every couple months, since that will destroy your hard drive if you over defrag.
With Windows XP if any programs (even those running in the background) or the screensaver interrupts the defrag, it will restart/hang. In Vista, the defrag is designed to defrag at a certain schedule in low priorty in the background. In order to defrag and use the PC at the same time you need to use an automatic defragmenter like Diskeeper which runs in the background in invisitasking mode and defrags silently without conflicting with other programs.
Local disk Properties > Tools Tab
It's a program to both optimise (defrag) the hard drive and clean up defunct programs.