One lesser known method of adding Ubuntu to a Windows PC is Wubi. This type of install uses a single big file within your Windows file system as the Ubuntu root disk and another one for swap. “Wubi.exe” is the installer that creates these files and configures the Windows boot manager for dual-boot. Since the installer is a Windows application, the file creation and boot manager configuration are done using native Microsoft code. One advantage of this type of install is that there’s no need to re-partition. Also Windows is booted without using a Linux boot manager like GRUB. So the impact on the Windows environment is minimal and Win 8.1 fast boot can still be used. Note that Ubuntu is booted using chain load from the Windows boot manager to GRUB.

What about the negatives? First and most importantly, Ubuntu accesses your disk through a “loop” file system, meaning that this big file within the Windows file system is used by the Linux kernel as “hard disk” which is formatted during Ubuntu install with a regular Linux file system such as ext4. This trick is the basis of all Linux Live CDs. So there is some disk IO overhead since “position within the ext4 partition” must be translated by the Linux NTFS driver to “position within the Windows partition”. My personal tests have shown that, since a disk seek time takes milliseconds and CPU cycles are measured in micro seconds, this overhead is low but YMMV! Apart from disk access, your Ubuntu install works just like any “normal” dual-boot install. This has nothing to do with virtualization!

It’s important to note that the files used by Ubuntu are impacted by a forced PC shutdown (pull the plug) just like any other NTFS file. Since ext4 runs “on top” of NTFS, the recovery of ext4 is impacted by how the NTFS file is recovered by Windows. On the plus side, it’s easy to back up your complete Ubuntu disk, just boot to Windows and copy the files. You could even switch Linux disks by swapping the files since the Windows boot loader uses a fixed filename and passes this info to GRUB which is installed on the “Linux disk”. I have not tried this so I might have overlooked something :-)

With Wubi, switching from Windows to Ubuntu is rather slow: after selecting Ubuntu in the Windows boot manager, your PC restarts once more before it transfers control to GRUB. Since this also happens when booting Windows VHD images, I think this is a Windows boot manager “limitation”.

So is this something for me you might ask. Most importantly, using Wubi the impact on an existing Windows install is low. Running Ubuntu within a virtual machine has lower impact but a (much) bigger performance penalty since then two OS-es are competing for the same resources. Only running Ubuntu from a Live CD or USB stick  has even lower impact but is performance wise the worst alternative.

If Wubi.exe does not show the install options, you might have started it from an Ubuntu CD or USB stick. Copy the Wubi.exe file to the Desktop and start it again. It’s just a small programmers trick to hide Wubi’s capabilities from the big public.

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