There are many difference but very few that have any impact on music production or Pro Tools. You can look into the detail here: http://windows.microsoft.com/en-GB/windows7/products/compare#T1=tab01 From our point of view the key difference is that Home Premium supports up to 16GB of RAM, so if you choose the 32GB option you will also need to choose Windows Professional. We also offer Windows Ultimate because it supports language packs, so if you wish to work in a language other than English then you should choose this option. With Windows 8 the RAM limit on the regular version has been lifted to 128GB so you only need to opt for Windows 8 Pro for the domain security and encription features.