One good idea is to run Verify Disk in Disk Utilities (/Applications/Utilities) on your main startup disk every now and then to identify problems, and watch the SMART status for your boot drive in Disk Utility too; it’s monitoring for signs of imminent failure. Oh, and never be tempted to install MacKeeper.
Do a clean install
Usually, a Mac that has slowed further and further down has just accreted apps, files and more, and one of the surest ways of restoring the pep and vigor it had out of the box is to wipe the hard disk, install a fresh OS, and then, crucially, don’t clone everything across using Time Machine or the like. Instead, manually copy all your documents across and reinstall your apps from the App Store or CD—omitting those you don’t need.
Credit: Christopher Phin
Yes, it’s usually a colossal pain, but it’s often the most effective way to reinvigorate your Mac if you can set aside the time and accept the temporary disruption.
Swap your hard disk for an SSD
Be sure you get the right form factor. For laptops and the Mac mini, this typically means a 2.5-inch drive—though the MacBook Air has always used more exotic and different options throughout its life—while for desktops 3.5-inch drives are more usual; this isn’t a hard-and-fast rule, though, so do check your specs carefully. 3.5-inch SSDs are rare, though they do exist, but you can convert 2.5-inch drives to 3.5-inch ones with a bracket; one might even be included with your 2.5-inch SSD, but if not, buy one separately. OWC even makes one specially for the 2009–2012 Mac Pro.
Check you get one with the correct connector, too. Most often these days that will mean a SATA connector, but you can buy SSDs with the older IDE/PATA/ATA connector from, say, Other World Computing; again, note that MacBook Airs use different connectors again. Note that with older Macs (definitely true for those with IDE, but also true for those with SATA I and SATA II connections), the connection to the motherboard itself will be a bottleneck, so don’t waste your money by buying anything other than a basic SSD; you don’t get the benefit of a high-performance model. Check your specs!
Credit: Christopher Phin
Any SSD, however, will have a completely revolutionary effect on a Mac that’s only ever known a hard disk; it will feel much more responsive, and even if you have a small amount of RAM—because of how low-RAM machines swap information out to the storage drive when there’s too much for the RAM to hold, and since SSDs are much faster especially at this kind of data transfer than a hard disk—swapping to an SSD will also help even if you don’t touch the RAM.
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