In any environment, in order to execute a privileged instruction you have have to switch from user mode to kernel mode, hence a context switch.

When a context switch occurs, the kernel saves the context of the old process into its Program Control Block and loads the saved context of the new process scheduled to run.

If the new context is already loaded into one of the register sets, a context switch involves simply changing the pointer to the register set in use. This is a faster operation as no actual data needs to be moved between memory and registers, resulting in a quicker context switch process.

The past tense of "not switch" is "did not switch" or "didn't switch," depending on the context.

If the process that gets the control can be put into the register (its kept in cache though) means less time to fetch and have a context switch.

Any way the context switching time isn't a big time delay.