Why doesn't Linux need defragmenting?

We have had a question or two in the OCLUG newsgroup and our chats about the Linux file system and how to maintain it. Ext3, the usual default file system in Linux distributions, is representative. Others, like versions of the Reiser file system are also common and Linux can interact with many different file systems.

Here is a not terribly technicall explanation of why Linux file systems do not need the most common maintenance operation present in Windows.

I will qualify the title, slightly. Occasionally, I have used a defragmentation utility on ext3 and ext3 systems that have been hit unusually hard by continuous file writes. It is a risky operation, really, because the utilities available are not equal to the highly developed ones for defragmenting Windows. In any event, in Linux they are not often needed. Almost never, in fact. Which is why I am not making a big thing about the title of this.

Jack