Back in what my old man calls "the Day," or "the 'so-called' Day," as I good naturedly joke back to him about it, the hippest computer operating system most personal computer operators used was DOS, which is the acronym for DISK OPERATING SYSTEM. And the first and most obvious difference between DOS and the operating systems our generation is familiar with (Windows XP, Windows ME, Windows 2000, for example) is that DOS was COMMAND LINE BASED, whereas our modern day systems employ a GUI, or Graphical User Interface. In other words, DOS users TYPED in all their commands and didn't even have a mouse to click. Below is what my dad saw when he used the DOS interface:
Black background and grey letters. No pictures or icons or tabs. No graphical-clickable things of any kind at all. Just letters and numbers and symbols and a place to type in commands, that is, directions or instructions for the operating system to perform both routine and complex functions that we take for granted today with the "programming" all invisible and behind-the-scenes. Back in the so-called day, however, they had to type in essentially every single step of every single process they wanted to run.
That's what the "C-prompt" was used for. See on the bottom of the interface window where there's a Capital C, colon, backslash, close bracket, and underscore ( C:\>_ )? The underscores "blinks," and that's where the DOS user typed in commands, hence "Command Line."
Below is the typical Windows XP desktop, a modern graphical user interface:
Yes, look what we have instead: Color, a background image (replete with blue sky, clouds, green fields, and photographic detail); shortcut icons, like the folder labeled "My Documents," which we can click to open an entire library of stored files we've created, and the "My Computer" icon, which we can click to open assorted nooks and crannies of our whole computer system; a "Start" button in the bottom left corner, which we can use to log on to our computer if it's on a network, reboot or shut off our computer, and access a variety of folders and settings and programs; a "Quicklaunch Toolbar," where we can keep miniaturized icons/shortcuts to our favorite programs and folders; and a "System Tray," which displays icons of system functions presently activated and crucial to the smooth running of our basic computer processes.