Consider a system that has a 16KB address space and 64 byte pages in a two-level page table. How many pages are required to store the page directory (assuming each page directory entry (PDE) is 4 bytes)?

Suppose there are two processes P1 and P2 whose 1KB address spaces are allocated in physical memory with base relocation (only base, no bounds). Suppose P1 has a base equal to 1024 and P2 has base equal to 4096. Which of the following virtual memory addresses can P1 use that will give it access P2's memory?

The following C code was our first attempt to make a lock using a flag to indicate if the lock was acquired.

typedef struct __lock_t { int flag; } lock_t;
void init(lock_t *mutex) { 
  mutex->flag = 0;
}
void lock(lock_t *mutex) {
  while (mutex->flag == 1)  // TEST the flag
    ;  // spin-wait (do nothing)
  mutex->flag = 1;  // now SET it !
}
void unlock(lock_t *mutex) {
  mutex->flag = 0;
}

How will this code perform in terms of correctness and efficiency?