Multimedia Class Scheduler (MMCSS) Service Defaults in Windows 11
Enables relative prioritization of work based on system-wide task priorities. This is intended mainly for multimedia applications. If this service is stopped, individual tasks resort to their default priority.
Default Settings
| Startup type: | Automatic |
| Display name: | Multimedia Class Scheduler |
| Service name: | MMCSS |
| Service type: | kernel |
| Error control: | normal |
| Path: | %SystemRoot%\system32\drivers\mmcss.sys |
| Registry key: | HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MMCSS |
Default Behavior
Multimedia Class Scheduler is a kernel driver. In Windows 11 it starts automatically during the operating system startup. If Multimedia Class Scheduler fails to start, the failure details will be recorded into Event Log. Then Windows 11 should boot up and notify the user about the MMCSS service startup failure.
Restore Default Startup Configuration of Multimedia Class Scheduler
1. Run the Command Prompt as an administrator.
2. Copy the commands below, paste them into the command window and press ENTER:
sc config MMCSS start= auto
sc start MMCSS
3. Close the command window and restart the computer.
The MMCSS service is using the mmcss.sys file that is located in the C:\Windows\system32\drivers directory. If the file is removed or corrupted, read this article to restore its original version from Windows 11 installation media.