Written by Topher Kessler
If you have many files on your hard drive and have extensively used it (i.e., updating your system many times), you may not be able to install Boot Camp and will get an error regarding the inability to partition and set up the drive.
Apple Discussion poster "TAGVoar" writes:
"I have an iMac 24" that I want to use Boot Camp on. When I try it says I need to reinstall Mac OS X fresh then use Boot Camp."
This error happens because unmoveable system files are scattered too sparsely on the drive, and Boot Camp needs a continuous section of the drive to partition for use with Windows. There are several ways to get around this:
Clone and restore
If you have a second hard drive handy, clone your boot drive to it either using Disk Utility or a third-party cloning program. For more information on cloning your drive, read our article on information and recommendations for cloning hard drives. After the drive has been cloned, be sure you can successfully boot off it.
Time Machine restore
If you do not have a spare drive, but are using Time Machine to back up your system, you can erase your drive and partition it how you would like (One being Mac OS Extended and the other being NTFS or FAT32), and then boot off the Leopard DVD and restore your OS X system to it. Then you can run the Boot Camp assistant to install Windows on the second partition.
Optimize with a drive utility
While Apple does not provide a disk defragmenter, several third-party utilities such as DiskWarrior and Drive Genius have this feature. Launching them and optimizing the drive will preserve the current partition scheme and move all files to a continuous location on the drive (you may need to use a boot DVD to perform these tasks properly). This will keep the current partition scheme intact and you can then partition and set up Windows with the Boot Camp assistant.
Reinstall Mac OS X
If you do not have a full system backup, and do not have a spare drive with which to clone your system, then reinstalling OS X may be your only option if you also do not have a copy of a defragmentation utility. This has the benefit of giving you a fresh installation of OS X, and while it is also what the Boot Camp assistant recommends, it is the most cumbersome option so we only recommend it as a last resort.
Topher has been an avid Mac user for the past 10-15 years, and has been a contributing author to MacFixIt for just over a year now. One of his diehard passions has been troubleshooting Mac problems and making the best use of Macs and Apple hardware both for family and friends, as well as in the workplace. He and the newly formed MacFixIt team are hoping to bring enhanced and more personable content to our readers, and keep the MacFixIt community going here at CNET. If you have questions or comments for Topher or the other MacFixIt editors, feel free to contact us at http://www.macfixit.com/contactResources