Tiny Core Linux (http://www.tinycorelinux.com) is a very unique distribution of Linux. Not only is it extremely small (the Tiny Core ISO download file size is only 12 MB) but it has a very unique file architecture and bootup process. Tiny Core runs from RAM and is extremely fast. Each time the system is booted the running system is assembled from several different places - the Tiny Core initrd, the extensions, and the backup file. This means each time you boot you get a very predictable system that is very resilient and reliable.
Tiny Core is very different from every other OS I have seen, and because of this there is a learning curve. But once you understand the principles behind Tiny Core you can really appreciate the benefits it has to offer.
Here is a video I created that shows an overview of the Tiny Core Linux file architecture and bootup process. Thanks to my wife who narrated the video.