Its not your imagination: your Macs overall performance can slow down over time. Most often this happens because we gradually add more apps and background processes, have more and more documents and browser tabs open, and dont restart very often. All these things take a cumulative toll on your Macs performance. Cutting back on the number of things you have open is therefore one of the easiest strategies for putting some zip back into your Mac. Adding RAM (if your Mac supports it), switching from a hard drive to an SSD, and keeping your software up to date are also effective quick fixes for performance problems.
But if I may rant for a moment, I want to call your attention to two oft-touted remedies for slow Mac performance that usually have so little effect as not to be worth the effort: freeing up disk space and defragmenting hard drives. Thats not to say these procedures are pointless or that they never help, but as with repairing permissions, their curative properties are greatly overestimated.
Fortunately, you can prove (or disprove) the effectiveness of such remedies using science! Benchmarking utilities can provide you with cold, hard, numerical factsif you take the time to use them properly.
Lots of utilities can locate and delete duplicate or excessively large files, old caches and logs, unwanted apps (and their supporting files scattered all over the place), unused fonts, and countless other types of data that may be cluttering up your disk. Im all for tidiness and saving disk space, and I appreciate the time and effort such apps save me.
But what bugs me about much of this software is the claim, repeated endlessly in ads and marketing copy, that deleting all this digital detritus will speed up your Mac tremendously. The implication is that theres a direct correlation between performance and disk space used.
Theres a kernel of truth in this claim. The true part is that OS X needs some breathing room to store things like virtual memory swap files; temporary files used when installing software; RAM images created when you put your laptop to sleep; and scratch files for audio-, video-, and photo-editing apps. If you run out of breathing roomwhich happens only when your disk is quite close to being fullOS X will indeed slow down, sometimes to the point of being unusable. Free up enough space, and performance should return to normal. (The need for breathing room is as true for solid-state storage as it is for hard disks, although SSDs should exhibit less pronounced speed reductions as you approach maximum capacity.)
Exactly how much free space you need to prevent performance degradation depends on quite a few variables. As a rough rule of thumb, I recommend 4 GB plus the amount of physical RAM you have installed as a reasonable minimum. But notice that this figure is independent of the size of your disk. In other words, if you have a MacBook Pro with 16GB of RAM and a 1TB disk with 990GB occupied, youre in the danger zone. But put the same files on a 2TB disk and you have loads of breathing room. In the first instance, pruning 100GB of unneeded files might have a miraculous effect on speed, while in the second, you probably wont notice any improvement at all.
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