I've swapped CPU on my HP550 laptop from T5270 Merom to T8300 Penryn... I am just wondering. Everything works fine and the speed boost is incredible... But Penryn has SSE4.1 and few other features... is Windows 7, XP or whatever aware of these features after CPU upgrade? Or all instruction set flags are present and asked before execution of each application(where ever it was compiled with option to use additional instruction sets). That may be truth about 3rd parity apps. Although what about the core services of the OS, I guess they work the same way? I hope you did catch the idea. Does the config of the OS core proceed during install of the OS or later on it can also be adjusted just as the new CPU drivers become active? Or there is some dumb registry made hack needed afterwards - as usual for windows like making tweaks for SSD work and core parking disabling, L3 cache etc) PS. Answer - just reinstall is rejected, I want to know it for educational purposes.