And it enables you to have a huge hard drive at a good(ish) price. A 27in iMac has a 1TB HDD for £1,499. A 1TB Fusion Drive costs an additional £200. You can't even get a 1TB SSD drive, the closest you'll get is a 768GB SSD drive that costs a whopping £720 more.
The shame with a Fusion Drive is that there's no way to add one to an older Mac, you can only pick it up with the latest iMac and Mac mini. However we do consider it well worth the investment.
Installing an SSD into a Mac
Whether or not you can upgrade a HDD to an SSD in a laptop depends on the model you've purchased. Currently the MacBook Pro 15-inch, Mac mini and iMac 27-inch are the only models that you can swap out the hard drives on (these will be joined with the new Mac Pro later in the year). The MacBook Air and newer MacBooks have their memory fixed to the motherboard, and the smaller iMac's hard drive is inaccessible.
If you have an older Mac you can check if the hard drive can be upgraded to an SSD. A good place to look on information regarding the upgrade, and how to about can be found on the iFixIt.com website.
If you can't install an internal SSD drive then you could consider a new SSD Thunderbolt powered external drive, like this Buffalo MiniStation Thunderbolt. This enables you to expand your storage levels without sacrificing on speed.
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