So your Mac isn't performing as it used to and needs a speed boost. You think back to what you used to do on your old PC and remember disk defragging. That should have the same effect on Macs, right? After all, it made your old PC run a lot faster.
Sadly, that's not the case - even though Windows has always had disk defragging software (even if it has been renamed to "Optimise Disk" in recent OS releases), Apple has never included defragging software in OS X.
"Why's that?" you may ask. Well, to put it simply, Macs don't typically experience the same fragmentation that Windows PCs are prone to. Before we go on to that, it's probably best to explain how data is written to a drive and why PCs need to be defragged.
Why do we defrag?
Typically, hard drives, or HDDs, are fastest at the beginning (the outside edge) of the drive and slowest at the end (or inside) - as you might imagine. New data is usually written on the outside of the drive, slowly working its way in as other data is added.
The issue is that the data doesn't move back outwards to take any available space, so holes start to develop with lots of reads and writes. As well as this things can become out of order, meaning the heads have to travel all over the drive to load files or programs, making the system slower on the whole.
Simply put, defragging a drive traditionally moves everything back in order and fills any holes that have appeared during its use.
How to defrag a Mac - and why you don't really need to, most of the time
Looping back to the previous point, Macs don't generally need to be defragged. This is simply because the Mac OS X file system was designed differently to Microsoft's, and it automatically defragments files on its own. The process is otherwise known as Hot File Adaptive Clustering (HFC).
That's not to say that a manual defrag is never needed, though; it's just rare. People (usually creatives) that have hundreds of films/audio/multimedia files larger than 1GB may need to defrag a Mac. The HDD also has to be pretty old to merit a defrag, as performance deteriorates over time.
In these rare cases where a defrag is needed, you'll need to use some third-party software. We reviewed one particular piece of software six years ago. iDefrag received a Macworld Editors' Choice award in our review, and we felt confident recommending it - but we can't comment on its development and effectiveness since then. Coriolis Systems has assured us that it still offers the reboot and defrag feature, although it's worth noting that you need version 5.0.1 for OS X 10.10 and 5.1.1 for OS X 10.11. Don't worry though, as the software should be unified with version 5.1.2 which is due for release soon.
Sign up for CIO Asia eNewsletters.