Apple usually has some pretty great (albeit expensive) storage options when you purchase their computers online or in-store. One element that was missing from the iMac line was the flash-storage option, something that appears to have been remedied.
The current iMac line ships with the 1TB hard-drive, more than enough room for your average consumer and even enough to please the picky downloader. If you rather have more speed than space, then a flash-drive is probably first on your list of choices. If you choose the lower-priced 21.5″ or the 27″ models then you have two choices ($300 for the 256GB version, and $600 for the 512GB option).
If you choose the larger 27″ model then you can choose the very impressive 768GB flash drive, but be warned, it costs $900 or about the same price as buying another Macbook Air. Apple wasn’t available for comment but it appears this option is only available online.
more info: apple