QUOTE(kryogenix @ May 31 2005, 3:00 PM)
It can be a lot like Windows.
http://www.kde.org/screenshots/images/3.2/snapshot11f.pngThat's a KDE desktop. It's not that much different now is it?
What distros do you run?
Well, Linux can be made to
look like Windows, certainly, and even behave like Windows in some ways (such as with the use of a desktop environment like GNOME or KDE), but the underlying system is still very different. A perfect example is in the way Linux handles drives: every drive on a Linux machine, from the internal hard drive down to the floppy drive, is mounted under a unified file system. For example, I have an account on a Sun workstation running Solaris (which is a Unix-based OS, like Linux). My home folder, where I store all my files and binary executables, is mounted under that workstation's filesystem; but really, it's on a networked server. In Windows this would appear as a separate networked drive, but in Linux, it's treated as being right there, at my computer. (In fact, in Linux, there are only a few directories that need to be stored locally: /boot, /root, /etc, /bin, and /sbin are the most crucial ones).
Linux also lacks a registry as in Windows (although GNOME has something like the registry, unfortunately), and even handles file permissions differently.
Linux also lacks the unified structure of Windows. Windows has only one desktop environment/window manager: explorer.exe. (Technically you can install other ones, but for all practical purposes, explorer.exe is the only one that is completely compatible.) Linux, on the other hand, has numerous desktop environments: GNOME, KDE, and Xfce are three. It also has myriad window managers: Sawfish (default GNOME window manager), kwm (default KDE window manager), Enlightenment, Fluxbox, and AfterStep, to name but a few. I can even mix and match environments and managers; for instance, I often run GNOME with Enlightenment. Linux can also be run completely from a command line, which is nearly impossible in Windows. (And when logging into my Linux machines remotely, I often do run only with a command line, as it takes a lot of bandwidth to run a GUI session.) In fact, many things that require a GUI in Windows can be done in with the command line in Linux.
As I also noted, Linux software often must be compiled from source code, or is packaged as an RPM that is generally installed via the command line. Software is rarely packaged as a neat GUI installer as it is in Windows. You also often times have to "play" with software, especially drivers, to get them to work in Linux.
There are, of course, a lot of under-the-hood differences in terms of architecture, such as the way memory is handled and files are written to the drives, and how the OS'es recover from errors. Basically, though, Linux can be made to appear like Windows, and if you only play with it a bit, you might not notice a lot of differences; but if you dive deeply into it, you'll notice some big changes.
As far as distros go, I personally use Fedora Core 3 on my main workstation, and Ubuntu Linux on an old iMac (I really don't like Ubuntu, but it's the only decent PowerPC distro I have found). I also often use a Sun UltraSPARC running Solaris, which is similar in nature to Linux (especially since I run Solaris in GNOME, not Sun's yucky Common Desktop Environment).