Multimedia Class Scheduler (MMCSS) Service Defaults in Windows 7

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:share
Error control:normal
Path:%SystemRoot%\system32\svchost.exe -k netsvcs
Registry key:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MMCSS
  • SeIncreaseBasePriorityPrivilege
  • SeImpersonatePrivilege

Default Behavior

Multimedia Class Scheduler is a Win32 service. In Windows 7 it is starting automatically on the operating system startup. Then the Multimedia Class Scheduler service is running as LocalSystem in a shared process of svchost.exe. Other system components, such as drivers and services, may run in the same process. If Multimedia Class Scheduler fails to start, Windows 7 attempts to write the failure details into Event Log. Then Windows 7 startup should proceed and the user should be notified that the MMCSS service is not running because of the error.


If Multimedia Class Scheduler is stopped, the Windows Audio service fails to start and initialize.

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.dll file that is located in the C:\Windows\system32 directory. If the file is removed or corrupted, read this article to restore its original version from Windows 7 installation media.