Let the time taken to switch between user and kernel modes of execution be $t_1$ while the time taken to switch between two processes be $t_2$. Which of the following is TRUE? (A) $t_1 > t_2$ (B) $t_1 = t_2$ (C) $t_1 < t_2$ (D) nothing can be said about the relation between $t_1$ and $t_2$

• Mode switch ($t_1$): Involves switching CPU execution mode between user mode and kernel mode (e.g., during a system call or interrupt). It requires saving only minimal context (such as program counter, stack pointer, and CPU status registers) without changing the address space or flushing the TLB/cache.

• Process context switch ($t_2$): Involves saving the entire process context (PCB, all registers, memory mapping tables) and switching the address space to another process (which typically involves flushing the TLB, changing page directory pointers, and cache misses). A process switch usually includes at least one mode switch.

Therefore, a mode switch is significantly faster than a full process context switch, so:

Hence, option (C) is correct.