XBM is the extension given to older format files that were associated with the X Window System. XMB are files used to store bitmap images. Technically, the XMB file is a text file containing the source code in the C language. On its basis, the system generates an appropriate image. XMB files most often contained the definitions of cursors or icons used in the X window graphical interface.

Today, XMB files are rare and the format is considered obsolete. The X Window System, also known as X11, was developed at the Massachusetts Institute of Technology by Bob Scheifler.