Commit 3728ace

@@ -255,6 +255,28 @@ Instructions: Please answer the following questions in about 1-2 pages each.
     [source][geeks-von-neumann]
 
 1. Define system call, and list the main types of system calls. Elaborate on how a system call interacts with a standard C library and hardware under a dual-mode operating system environment. (10 marks)
+
+    The two types of systems call modes are kernel mode and user mode.
+    With a mode bit we are able to determine if a task is being executed on behalf o
+    the operating system or the user. A user may request a service from the
+    operating system via a system call. In this case the system call
+    will transition from user mode to kernel mode to perform the request then
+    transition back to user mode once the request has been fulfilled.
+
+    ```plaintext
+    user
+      [process] -> [system call]   [return from system call]
+                       |                   |
+                  (user mode)         (user mode)
+    -------------------V------------------ A-----------------
+    -------------------V------------------ A-----------------
+    kernel             |                   |
+                 (kernel mode)             |
+                       |                   |
+                     [execute system call]-|
+    ```
+
+
 1. Describe the overall structure of virtual machines, and compare VMware and JVM. (15 marks)
 
 # Sources: