Up until recently, it was not possible to equip your iMac with an SSD. This excludes the 27" model, which could only be equipped with a 768 GB SSD for a massive price of about $1400. Beyond this, the closest that iMac buyers could get to equipping their iMacs with an SSD was by choosing Apple's so-called "Fusion Drive". The Fusion drive is essentially a 128 GB SSD that gets used as a caching SSD alongside a traditional hard drive. Supposedly the iMac would boot up 70 percent faster and import files up to 350 percent faster. A caching SSD places the most used files and programs on the SSD storage (As well as leave it on the hard drive) for faster access and throughput.
Now however, Apple has expanded the options for storage on the iMacs. The SSDs that can be chosen will cost $300 for the 256 GB model, $600 for the 512 GB model, and $900 for the 768 GB version. Unfortunately, for those who aren't interested in a 27" iMac, but want the 21.5" model, this machine cannot be configured to have either a 3TB hard drive, a 3 TB Fusion Drive, or a 768 GB SSD.