GTX 580: On the outside
Nvidia made a lot of changes to how GeForce GTX 580 handles heat, voltage levels and noise output. The printed circuit board (PCB) is exactly the same length and width. GTX 580 and 480 are shorter than Radeon 5870 but longer than Radeon 6870, 6850, and 5850. The first change you can see is to the cooling system. In the image below there is a lack of plumbing extending out the side of the shroud compared to GeForce GTX 480. Another change is the shape of the cover. The top has been beveled to allow better access of air to the intake. While in a single card configuration this should not impact cooling performance. However, for SLI and Triple-SLI in tight cases this should help improve airflow.
The next change that you can visibly see is the new cooling system. The lack of plumbing extending out the side of the shroud compared to GeForce GTX 480 is clearly visible in the image below. Additionally, Nvidia made the intake opening 10mm wider in diameter. GeForce GTX 580 is 65mm wide while GTX 480 is 55mm.
Flipping the cards over you will see that Nvidia removed the hole in the PCB, GTX 480 had this space to gain additional air which could be drawn into the fan. In its place on GTX 580 is some new voltage monitoring circuitry. In the image below you can see it located on the top side of GTX 580ís PCB. There are three separate units. Each one monitor a different 12V power connection (8-pin, 6-pin and PCI Express connectors). Nvidia states that this is to adjust performance when certain applications that stress the cardís power draw beyond the shipping specifications. While over-draw protection is great for the general consumer, we are not so sure it will be received the same by extreme overclockers.