CSE 120 -- Homework #1

Out: 9/28/00
In: 10/5/00

1. Chapter 2, Section 2.6: 1, 3, 11
2. Chapter 3, Section 3.15: 1, 3, 14, 16, 31
3. Which of the following instructions are privileged?
   • Set value of timer
   • Read the clock
   • Clear memory
   • Turn off interrupts
   • Switch from user to kernel mode
4. Protecting the operating system is crucial to ensuring that the computer system operates correctly. Provision of this protection is the reason behind user/kernel operation, memory protection, and the timer. To allow maximum flexibility, however, we would also like to place minimal constraints on the user. The following is a list of operations that are normally protected. What is the minimal set of instructions that must be protected?
   • Change to user mode.
   • Change to kernel mode.
   • Read from kernel memory.
   • Write into kernel memory.
   • Fetch an instruction from kernel memory.
   • Turn on timer interrupt.
   • Turn off timer interrupt.