The CLTS instruction clears the task-switched (TS) flag in the CR0 register. This flag is set by the processor every time a task switch occurs. The TS flag is used to manage processor extensions as follows:
Thus, if a task switch was made after an ESC instruction was begun, the floating-point unit's context may need to be saved before a new ESC instruction can be issued. The fault handler saves the context and clears the TS flag.
The CLTS instruction appears in operating system software, not in application programs. It is a privileged instruction that can only be run at privilege level 0.