A command line interface (CLI) OperatingSystem is one that requires the users to type in a series of commands in order to tell the computer what to do: the equivalent on clicking on a button in a GraphicalInterface OperatingSystem, only the user is directly involved in the operating of the computer.
This kind of OperatingSystem is very popular with programmers and webmasters alike, because it in no way cushions you from the computer itself, allowing a huge amount of customisability.
A command line interface OperatingSystem like DOS or Unix allow more control over the machine. In a GraphicalInterface OperatingSystem , generally speaking, the user is more protected from what they can do and in most cases, if they can't SEE something then it doesn't exist. If you're browsing your computer in DOS, use dir /a instead of dir, it will show files with any attributes, allowing you to see hidden folders and those pesky dynamic folders that internet explorer generates. Using DOS gives you greater control over the machine, from it you can directly access things like the environment table. This is very useful for modders and programmers alike. Personally, i always have a command window open when i'm running Windows, just in case i need something done quickly that's easier to do from DOS. CommandLineInterface languages are also great for your typing speed. For you windows users (non-2k/nt), use DOS for a day or two to do everything you would normally do (on your hd at least) and you'll notice the incredible increase in speed. -- CJSilver