If you are using Windows 7 on an old PC with less graphics or want to make Windows 7 faster, then you must use the Basic theme. Windows 7 basic theme is without Aero and is certainly very light as compared to Aero theme.
Basic theme is non transparent, doesn’t show applications preview in taskbar and disables Aero Peek. To enable it, open Control Panel > Appearance and Personalization > Personalization. Under ‘Basic and high contrast themes’ select Windows 7 Basic.
Now you’ll notice a huge improvement in your Windows 7 system speed. It is highly recommended for office users and people preferring simple look.