1. In using semaphores to control access to a critical section, we initialize the semaphores counter to 1. What happens if we initialize it to 0? to 2?

2. Race conditions can occur if two or more processes can access a shared object at the same time. Suppose there are five processes, A, B, C, D and E. Is there a race condition if all five of these are using the same critical section at whatever times they like, if no one of these processes (nor any other) is able to modify values in the critical section? How is the answer different if only one of the processes can modify values in the critical section, or is there no difference between these two cases?

3. In describing messages used in most message passing systems, it was observed that header information was usually fixed-length but the data in the message (often called the payload) was usually variable length. What makes this a very efficient way to handle messages, i.e., why is it efficient for headers to be fixed length and payloads to be variable length?

4. There are two ways to know where the end of a variable length item, like a message payload, is. What are they? Which one does the Internet Protocol v4 use?