Windows Vista: Click Start/Vista icon, go to Computer. Under the Local Disk (c:) it tells you how much free space you have compared to the total space in your computer.
Windows XP: Click Start then click on Control Panel. Open My Computer. Right click on Local Disk (c:) and select Properties. You will see a pie chart detailing your free disk space in the General tab.
Windows 7: Click on the Computer Icon. You’ll see each drive with a small percentage bar of how much disk space is being used as well as a description of how much is free and the total disk space. If you’re wanting additional information right-click the drive and click Properties.
Macintosh: At your desktop, single click on Hard Disk icon to highlight, then click on File, and drag down the Get Info. The window “Hard Disk Info” will open. Look for Size