What you are heAring about are the Seagate Momentus XT series. The are 2.5-in formfactor drives, 9.5mm thick, and come in several sizes. The can replace regular HDDs in most laptops. Some of the newest, however, will only take 7mm thick drives - that is what many of the top SSDs are.
There is an enormous amount of traffic in the Anandtech forum that you can access so we don't have to reinvent the wheel.
I have used 6 of these hybrids with great success.
CorkyG - Tucson, AZ
In my view you cannot claim to have seen something until you have photographed it.... Emile Zola