What is the difference between Ubuntu server and Ubuntu Desktop?

[McMichael96]

I use Ubuntu 9.10 Desktop(and use way more then Windows Vista ) I was just wondering if i could use a computer with Ubuntu server and use that computer for backing up and sharing files plus to use it as a fire wall for my other computers! Thanks.

[memilanuk]

There are some specific optimizations in the kernel that ships with Ubuntu Server that are not present in the Desktop version. It's not so much that you can't run a web, database. or file server on a computer with the desktop version... its just that if you are going to really work it hard, the server-optimized version might respond better. For casual home use, you'll likely never notice the difference.

Many other distros don't have a separate kernel specifically for the server edition and they seem to manage just fine

The Ubuntu Server install comes default with no GUI interface, and is somewhat spartan. Generally speaking, it's somewhat easier to add the desired server software to a PC running the Desktop edition, than it is to get all the GUI stuff up and running on a machine running the Server version.