As the size of a HTPC shrinks, so do the performance and upgrade options. You're generally stuck with Micro-ATX or the like for motherboards which offer fewer features than their full-size cousins. Things like riser cards and slim CD/DVD drives add to the cost and you're lucky if you get two hard drive bays and a single 5 1/4" bay. Few slim HTPC's support a full size power supply and don't even think about high-end video cards and cooling.



Link: PCApex