A seemingly unavoidable trait of all operating systems is the notorious slow-down – it doesn’t seem to matter how nicely you treat the system, after a few months it’ll start grinding to a halt (or is it just me?). This has happened to me in Windows, Linux and OS X, and it drives me absolutely crazy. The only way I knew to go back to a zippy system was to reinstall the whole system, which is pain, pain, pain.

An operating system divides the filesystem up into fixed-size blocks, which it reserves for storing files – as many blocks are needed to store each file. When you delete a file, it clears the associated blocks for later use. However, this inevitably leads to free blocks being located all over the drive, not in one contiguous segment, and that means that for the next file, blocks have to be selected that are located far apart on the drive. That means when that file is read, the hard disk has to seek all over to be able to gather all pieces of the file – slow.

A popular maintenance task for Windows users is defragmentation – this takes all the used blocks on the drive, and clusters them all together at the start of the disk, so that blocks containing data for the same file are located together, and the free space is all together. That means the system has less work to do to read files.

I’d read in several places (including Apple’s documentation) that defragmentation (otherwise known as ‘disk optimization’) isn’t really necessary on Mac OS X and probably won’t make much difference. Bollocks!

I just performed a defrag using the excellent Tech Tool Pro 4, which took around 24 hours (yikes); it made a huge difference to the snappiness of the system, though – comparable to when I entirely reinstalled the OS.

So, I highly recommend it – don’t listen to the nay-sayers, this makes a big difference. Just make sure you have the time to let the machine chug away for a day. Alternatively, just do a few hours at a time – you can stop it, and continue later.