Do you often have the need, or want the pleasure, to try a new operating system?
Do you prefer using a "real machine" rather than creating a virtual one (like VMware or Virtualbox for instance)?
Have you got a spare machine for this purpose?
Ok, if you responded "Yes" to all the above, please read on...
A hard disk can be divided in no more than four primary partitions. Microsoft Windows requires to be installed in a primary partition in order to boot. In some older versions it even requires to be in the first partition as Wikipedia says: "In DOS and earlier versions of Microsoft Windows systems, the system partition was required to be the first partition. Windows operating systems must be located in a primary partition. Other operating systems do not have this peculiar requirement."
Instead of creating four primary partitions one can be "sacrificed" to be an extended one. A hard disk may contain only one extended partition which can be subdivided into multiple logical partitions.
The only purpose of an extended partition is to contain logical partitions.
These can be used as normal partitions except for the fact that Windows cannot boot from them. Linux can... :-) Nice penguin!
So, this is the "secret". You can use logical partitions for installing all Linux flavours that you like so much and can't live without (SWAP and other OSs) and keep the primary partitions for the
To start partitioning your hard drive you can use gParted which is the best tool I've ever found for this purpose (or any other partitioning tool you like). gParted is included in Ubuntu but I'm quite sure it can be installed in other distros as well.
Now you should be ready to have a look at my experiment:
As you can see I created an extended partition in the first one ("/dev/sda1") and I kept a primary partition for Windows Xp ("/dev/sda2").
Inside the extended partition I've created six logical partitions for some linux flavours all functioning, plus a SWAP ("/dev/sda5") partition and a DATA ("/dev/sda12") partition used to share files among the OSs. I've choosen "fat32" since some Linux distributions don't support NTFS out of the box.
After all of this, my little hard disk still has 9 GB free. What other operating system should I install? :-)
All operating systems are managed by a boot loader (Grub2) which gives me the possibility to choose which OS to start. Grub2 is shipped with many recent distributions like Ubuntu Lucid for example.
In the near future I might write a post on how to recover a lost grub which makes the computer unbootable.
Enjoy the freedom to try all the operating systems you are curious about.