Commit 707ab72

@@ -34,7 +34,7 @@ Instructions: Please answer the following questions in complete sentences. Your
     ```
 
     Programs can also trap a signal and handle them. In the following example
-    the Ruby program is trapping the `SIGUSR1` signal to reload a configuration
+    the Ruby program is trapping the `SIGUSR1` signal to exit the program.
     file.
 
     ```ruby
@@ -66,35 +66,18 @@ Instructions: Please answer the following questions in complete sentences. Your
 
 1. How does a computer system with von Neumann architecture execute an instruction?
 
-    * fetch instruction from memory and store that instruction in the instruction register.
-    * decode instruction. may cause operands to be fetched from memory and stored in some internal register.
-    * execute instruction
-    * store result back in register
+    The first step is to fetch the next instruction to execute and put it
+    into memory. The instruction is given to the CPU and the program counter
+    is incremented.
+    The second step is for the CPU to decode the instruction and prepare to execute.
+    The third step is to execute the instruction. This may require the CPU to
+    utilize the ALU and control unit.
+    The fourth step is to store the result in a register or memory.
 
-    ```plaintext
-                      -------------
-                      | --------- |
-                      | | CPU   | |
-                      | | ----- | |
-                      | | |CU | | |
-                      | | ----- | |
-      ----------      | | ----- | |       ----------
-      | Input  |      | | |ALU| | | ----> | Output |
-      | Device |----> | | ----- | |       | Device |
-      ----------      | --------- |       ----------
-                      |   |  A    |
-                      |   V  |    |
-                      | --------- |
-                      | | MU    | |
-                      | --------- |
-                      -------------
-
-     CPU: Central Processing Unit
-     CU: Control Unit
-     ALU: Arithmetic/Logic Unit
-     MU: Memory Unit
-    ```
-    [source][wiki-von-neumann]
+    1. Fetch
+    2. Decode
+    3. Execute
+    4. Store
 
 1. What role do device controllers and device drivers play in a computer system?
 
@@ -132,8 +115,8 @@ Instructions: Please answer the following questions in complete sentences. Your
 
 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.
+    * 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
@@ -185,13 +168,21 @@ Instructions: Please answer the following questions in complete sentences. Your
 
 1. Describe some requirements and goals to consider when designing an operating system.
 
-    1. Provide a system call interface for user mode programs to use.
-    2. Provide compilers, linkers etc to build user mode programs.
-    3. Provide consistent abstractions to shield user mode programs from needing to know the details of each piece of hardware.
-    4. Can execute multiple tasks concurrently
-    5. Can operate against different combinations of hardware without impact to user mode programs.
-    6. Process management
-    7. Memory management
+    When designing an operating system it is important to consider the needs of
+    the runtime environment. Some questions to consider are:
+
+    1. Will there be a need to run multiple programs simultaneously?
+    2. Will there be a need to isolate programs from one another?
+    3. Will there be a need to build user mode programs to access privileged instructions?
+    4. Will there be a need for high availability and guaranteed uptime?
+    5. What types of hardware will the operating system need to work with?
+
+    These questions will help guide the design of a system call interface,
+    compilers, linkers and other build tools. It will help identify
+    the types of abstractions that the operating system may need to
+    provide and whether or not it will need to process multiple
+    tasks simultaneously or not. Finally, this will identify constraints
+    for process and memory management.
 
 1. Explain why a modular kernel may be the best of the current operating system design techniques.
 
@@ -245,6 +236,14 @@ Instructions: Please answer the following questions in about 1-2 pages each.
     ```
     [source][wiki-von-neumann]
 
+    In the von Neumann architecture an input device may trigger
+    a signal to be handled by the operating system. The control
+    unit will need to fetch the privileged instruction to place
+    into a register or the memory unit to provide to the CPU to execute.
+    The ALU will decode the instruction and then the instruction will
+    be executed. The result is then stored in a register or the main
+    memory unit to be written to the output device.
+
     * Input device: Includes keyboard, mouse, camera, microphone etc.
     * CPU: Contains the control unit, arithmetic logic unit and main memory
       * CU: Control unit handles all processor control signals. It directs I/O flow, fetches code for instructions and controls how data moves around.