I've got both an A and an S500. The A500 is with a K6-2 300 and the S is with my Duron 600@927. I wouldn't even think of putting a Duron in the A500 unless I did a lot of cutting to add extra cooling. The S500 has provision for a fan at the front-bottom and the back near CPU. I ordered an AMD-approved 300 watt PS with the S. Panels are very easy to remove/replace to get at dip-switches. The A has the removeable MB tray which I consider a worthless feature.