Windows

• 1). Choose an external hard drive at least as big as the drive already installed in your computer. If you've forgotten the hard drive size, go to "Computer" -- or "My Computer," depending on your version of Windows -- right-click on the hard drive, most likely the "C:" drive, and select "Properties." This will show you total space, used space and free space on the drive.
  
  
• 2). Start Windows' Backup Utility, found by clicking "Programs," "Accessories" and "System Tools," after plugging in your external drive. Follow the onscreen prompts to start a full backup, and then schedule incremental backups at your chosen intervals.
  
  
• 3). Download and install Carbon Copy Cloner (CCC) from bombich.com. CCC is a free program that can make a copy/clone of any hard drive, including the drive used for startup, which most programs cannot do without errors. After installation, select your computer's drive as your source drive, your external drive as your destination and click "Clone." CCC will clone the drive completely to a bootable volume.
  
  
• 4). Drag and drop your files. If you prefer, you can copy/paste or drag and drop individual files from your hard drive to the external drive, though it may take quite some time. However, if you do the work manually, you have more control over what gets copied and what doesn't.
  
  

Macintosh

• 1). Choose a drive at least as big as the hard drive already installed in your computer. If you've forgotten, click your hard drive icon in the left "Finder" window and select "Get Info." This will show you the size of the drive.
  
  
• 2). Start Time Machine. Time Machine is Apple's proprietary backup software that comes packaged with OS X. The first time you plug in an external drive, Time Machine will detect the drive and ask if you would like to use it for backup purposes. Follow the onscreen instructions, and Time Machine will move everything onto the drive -- constructing a full backup at first, and then an incremental one at whatever interval you specify.
  
  
• 3). Use Disk Utility to clone your hard drive. To do this, you must start up from the OS X DVD that came with your Mac. Put the OS X DVD in the drive and reboot the computer. You may have to hold down the "C" key to boot from the disk.
  
  Once the computer has started, open Disk Utility. Click the "Restore" tab. Select your Mac's hard drive as the source, and the external drive as the destination. Once you click "Restore," Disk Utility will clone your hard drive onto the external drive.
  
  
• 4). Drag and drop your files. If you prefer, you can open two "Finder" windows -- one with the contents of your hard drive, and the other showing the contents of the external drive. You can select individual files from the hard drive and drag them into the external drive window to copy. You can also select the files, select "Edit," then "Copy" from the desktop menu, and paste the file into the external drive window.