24GB SSD is cache drive used by OS through the Intel driver. As a user you don't see it, but it speeds up the disk access, sleep/ wakeup time, etc... it does make a very noticeable difference in real life.
Because it is an msata drive, you can always replace it by a bigger SSD and run it is a full fledged separate drive.
so there is an actual drive which is used as cache? which can be replaced with a real one at some point in a future