On the traditional hard drive there are a bunch of spinning disks with an arm that moves across to read the information. Think of an old fashioned record player only spinning at 7200 RPM, or faster. When you turn on the computer, or start using the machine, this drive has to spin up to full speed before anything can happen. Then the arm has to move across the disks to find the information you want.
The new, SSD (Solid State Drive) is just like a large thumb drive but it goes inside the machine. There are no moving parts which makes this MUCH faster, lighter, cooler operating, and uses less electricity. Another advantage is that, because there are no moving parts, it really can't be damaged by dropping the computer. (However, remember that anything will. eventually fail and you should have a backup of your data)
How fast? One example is my computer: Understand that I have a lot of programs that start with Windows (over 30). When I had a standard hard drive it took my machine almost 15-minutes from shut down to start up. My new drive takes less than 1 minute.
If you are interested let me know and we can discuss what it would cost and if it would be a good move for you.