Winding (XO) is the main computers Operating System in Angel Beats!. Its logo is depicted of a red, green, blue, and yellow spiral.
- Winding is a reference to the most popular computers Operating System in the world, Windows.
- Winding's publisher, MacroSoft, is a reference to Microsoft, being that "macro" is the antonym of "micro".
- The Winding boot-up screen is similar to the boot-up screen of that of Windows XP. XO is probably used because many fast typers usually hit the "O" key for "P".