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You’d put frequently used applications on the SSD and relegate everything else to the HDD. Fusion Drive is similar to what you’d do manually if you had a small SSD and large HDD in a single system. Fusion Drive appears as a single volume equal to the capacity of SSD + HDD, with the software layer intelligently managing what data ends up on the SSD and what ends up on the HDD. I put caching in quotes because Fusion Drive doesn’t actually act like a cache but rather a software managed, spanned storage volume. At a high level, Fusion Drive is a software managed SSD “caching” solution on top of a 128GB SSD and 1TB or 3TB HDD.
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I went through a deep analysis of Apple’s Fusion Drive with the 2012 iMac, so I’ll spare you the details here. Long term I believe Apple has a solution to this problem other than forcing everyone to accept a two-volume approach to storage (or, alternatively, dealing with small/fast local storage and putting everything else in the cloud). My guess is that Apple views the iMac as targeting a slightly different audience than those systems, an audience more used to large, single-volume storage. Both the MacBook Air and MacBook Pro with Retina Display are SSD-only, and the same will be true for the coming Mac Pro.
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The iMac is an unusual member of Apple’s Mac lineup in that it is one of the only systems to ship with a HDD by default.
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However, shooting for bearable is aiming too low in my opinion. OS X continues to do a great job caching frequently used data in main memory, something the iMac has plenty of in its default 8GB configuration, so the HDD-only option does quickly become bearable.
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It’s been quite a while since I’ve forced myself to use a system with only a HDD, and going back to one now just reaffirms what I’ve been thinking for a while: HDD-only systems have been killing the PC industry for a while now. MEMBER, A.K.W.By default all of the iMacs come with a 2.5" or 3.5” (21.5/27" iMac) mechanical hard drive.
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