describe modes of operation

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@@ -131,6 +131,16 @@ Instructions: Please answer the following questions in complete sentences. Your
     The users and clients of the applications see only a brief interruption of service.
 
 1. Describe an operating system's two modes of operation.
+
+    kernel mode: executes tasks on behalf of the operating system.
+    user mode: executes tasks on behalf of the user.
+
+    Whenever the operating system gains control of the computer, it is in kernel mode.
+    The dual modes of operation provides a way for protecting the operating system
+    from malicious behaviour. Instructions that can cause harm are treated as
+    privileged instructions. Privileged instructions can only be executed in
+    kernel mode.
+
 1. Define cache, and explain cache coherency.
 1. Describe why direct memory access (DMA) is considered an efficient mechanism for performing I/O.
 1. Describe why multicore processing is more efficient than placing each processor on its own chip.