Dual-Booting Windows and Ubuntu

Rarely, a user may experience problems dual-booting Ubuntu and Windows. In general, a Windows OS should be installed first, because its bootloader is very particular. A Windows installation usually occupies the entire hard drive, so the partition needs to be shrunk, creating free space for the Ubuntu partition. (You should clean up unnecessary files and defragment the drive before resizing.) See changing the Windows partition size. After shrinking the Windows partition, you should reboot once into Windows prior to installing Ubuntu or further manipulating the partitions. This allows the Windows system to automatically rescan the newly-resized partition (using chkdsk) and write changes to its own bootup files. (If you forget to do this, you may later have to repair the Windows partition bootup files manually using the Windows Recovery Console.)
If done this way, there is no problem installing Ubuntu as the second operating system and it is done automatically from the Ubuntu LiveCD. Allow the Ubuntu LiveCD to install to "largest available free space."
A Windows partition should be at least 20 Gb (recommended 30 Gb for Vista/Windows 7), and a Ubuntu partition at least 10 Gb (recommended 20 Gb). Obviously, if you have plenty of disk space, make the partition for whichever will be your favoured operating system larger. For a recommended partitioning scheme, see this section.
Alternatives include:

• Wubi (Windows-based Ubuntu Installer), an officially supported dual-boot installer that allows Ubuntu to be run mounted in a virtual-disk within the Windows environment (which can cause a slight degradation in performance). Because the installation requires an intact functioning Windows system, it is recommended to install Ubuntu in this manner for short-term evaluation purposes only. A permanent Ubuntu installation should be installed in its own partition, with its own filesystem, and should not rely on Windows.
• EasyBCD, a free Windows-based program that allows you to dual-boot Windows Vista and Ubuntu (as well as other operating systems) by configuring the Vista bootloader.