I have an XPS 15Z ordered with 256GB SOLID STATE DRIVE, and was so impressed with the speed that I have installed one in my XPS17.
This unit came with 1.5GB (2x750GB) DRIVES
I purchased a 128GB CRUCIAL SSD, cloned my 'C' drive and installed it myself. I'm not an expert, and found this chore easy to accomplish.
END RESULT: I CAN'T BELIEVE THAT THIS IS THE SAME LAPTOP! IT'S SO MUCH FASTER.
I WILL NEVER AGAIN PURCHASE ANY PC OR LAPTOP WITHOUT A SSD!
HIGHLY RECOMMENDED. Cheers.