The $100 laptop does not have a harddisk.  The designers of the $100 laptop found that hd's are one of the first things that often break in a computer.  To get around this problem they are using Flash memory.

Flash memory  is a solid-state memory.  In the most basic way that means it has no moving parts.  The iPod uses it.

Over the last several months I've wondered why I have such a "big" hd on my laptop.  I have 60 GB, but honestly I don't use it so often now.  I put my documents on servers - at work, my isp, services like snapfish.  Really all I need regularly is an internet connection, a browser and a place on the web I can lay my docs.  

I find it interesting that limiting things that we assume are "required" for construction of a computer we still have significant opportunities to create and share information in places that have limited resources.