What is the main difference between ultrabook and laptop?

Q. Hi, i want to buy a new laptop, should i buy ultrabook? What is the main difference? Thanks

A. The most important difference - it's size. Ultrabook has a size as a netbook or tablet, but it has a very high performance.
I really like this picture compare laptop and ultrabook http://ultrabooksreview.com/buying-advice/laptops-and-ultrabooks-a-world-of-difference/

What is the difference between havingor having not SSD to an ultrabook?

Q. I found a lot of uultrabooksare with SATA drive. So, ssd, is it big deal?

A. SSD are nearly 200% faster than a SATA HDD. An HDD has more storage capacity and a decent speed. (1-2 TB for 300$) A 128GB SSD is approximately 109$ To answer your question:

Yes, it is a big deal :)

Will a sata iii ssd work if i want to upgrade the ssd on my asus ultrabook ux31a?

Q. 128gb isnt enough for me. I want to double it but i dont want to cheap out on a sata ii ssd.

A. It WILL work, my friend, but the data throughput will be limited to SATA 2 speeds.