The Windows logo key (also known as Windows, win, start, logo, flag, OS, or super key) is a keyboard key which was originally introduced on Microsoft's Natural Keyboard in 1994. This key became a standard key on PC keyboards. In Windows, pressing the key brings up the start menu. Ctrl+Esc performs the same function, in case the keyboard lacks this key.
Historically, the addition of two Windows keys and a menu key marked the change from the 101/102-key to 104/105-key layout for PC keyboards. Compared to the former layout, a Windows key was placed between the left Ctrl and the left Alt and another Windows key and the menu key were placed between the right Alt (or AltGr) and the right Ctrl key.
The Windows key was introduced with Microsoft's Natural Keyboard in 1994. The first laptop series to bear Windows keys on its keyboard was the Gateway Solo. The key is predated by the ⌘ Command key on Apple computers in the 1980s, and before that by the Super (or Meta) key on Lisp/Unix workstation computers in the 1970s.
In laptop and other compact keyboards it is common to have just one Windows key (usually on the left). On Microsoft's Entertainment Desktop sets (designed for Windows Vista), the Windows key is in the middle of the keyboard, below all other keys (where the user's thumbs rest).