Debian is an extremely stable Linux distribution that includes a great variety of software that runs in many different environments and on many different CPU architectures. It is free, in the spirit of the Free Software Foundation's definition, and thus may be run freely on as many systems as an administrator desire, without limit or licensing fees. It may be freely copied, modified, and re-distributed. Debian is available from many official Debian servers and mirrors, and it is well supported by an official and well-defined, albeit all-volunteer organization, which provides support via many channels. Paid installation media and support are also available from many third parties.
Debian installations tend to install the minimum services necessary, requiring the administrator to add any additional services necessary after the initial installation. This results in systems that are secure, run faster without unnecessary services and allows Debian to work satisfactorily on older, less capable systems.
Now that we've covered the basics of Debian, it's time to cover the basics of disk layouts, including the structures used for booting and how to determine the partition layouts.