Stores system settings and variables used by the DOS and Windows operating systems; also contains functions that are used to run the operating system; SYS files typically should not be edited.

IO.SYS is used by DOS and Windows 9x; it contains the default DOS device drivers, the DOS initialization program and processes MSDOS.SYS and CONFIG.SYS files.

MSDOS.SYS contains the core operating system code for DOS, known as the DOS kernel; CONFIG.SYS is the primary configuration file used for the DOS operating system.

Device driver used by Motorola cell phones; allows the phone to communicate with computer and transfer files to and from the device; typically installed with the software installation CD included with the cell phone.

Example Motorola driver files include the "m56pci.sys" device controller and the "p2k.sys" file, which enables the P2Kman program to upload and download files from Motorola Vxxx cell phones.