The sysinfo (MCI_SYSINFO) command obtains system information about MCI devices. MCI handles this command without relaying it to any MCI device. For the command-message interface, MCI returns the system information in the MCI_SYSINFO_PARMS structure.
You can use the sysinfo (MCI_SYSINFO) command to retrieve information such as the number of MCI devices on a system, the number of MCI devices of a particular type, the number of open MCI devices, and the names of the devices. This command is often called more than once to retrieve a particular piece of information. For example, you might retrieve the number of devices of a particular type in the first call and then enumerate the names of the devices in the next.