I am using windows 8.1 for optisystem on my laptop, and windows 7 for optisystem in the lab. If i were to compare the both with regards to optisystem performance, then windows 7 is more smoothly functioning (It seems to experience unexpected crashes/issues more often in windows 8.1). But all in all i would prefer windows 8.1 to windows 7 considering everything i use the OS for.