For myself and a customer I am considering the new iMac. One of the options is to install a Fusion Drive.
AnandTech about Fusion Drive:
The new iMac and Mac mini can be outfitted with a Fusion Drive option that couples 128GB of NAND flash with either a 1TB or 3TB hard drive. The Fusion part comes in courtesy of Apple’s software that takes the two independent drives and presents them to the user as a single volume. Originally I thought this might be SSD caching but after poking around the new iMacs and talking to Apple I have a better understanding of what’s going on.
The OS and other stuff that you use often will be placed on the SSD automatically. So for that kind of stuff the thing will feel like a 100% SSD. For other stuff, like photos, I expect it to be slower. But that is not a problem, since you don’t use those a lot.
The concept is interesting, at least for mainstream users. Power users will still get better performance (and reliability benefits) of going purely with solid state storage. Users who don’t want to deal with managing data and applications across two different volumes are still the target for Fusion Drive (in other words, the ultra mainstream customer).
The problem with the iMac is that it has only a single HDD slot. So you have the choice of Fusion Drive or not at the moment of ordering. I expect the flash to sit on the mainboard. Considering the next video and considering the performance of pure SSD machines like the Macbook Air, your only choice is to buy it, since you cannot install it afterwards you will regret it later.