Question 3 (18 points, 30 minutes)

Part 1 (12 points)

Describe (in English, not using code) how Unix's malloc() and free() work.

Part 2 (6 points)

When the following program reaches the HERE line, state how many bytes have really been allocated in the heap. Partition these bytes into:
  1. Bytes that user user thinks he has allocated.
  2. Bookkeeping bytes.
  3. Bytes of padding.
  4. Bytes in the free list.
Assume that malloc() calls sbrk() in 8K chunks. 
typedef int int253[253];
main()
{
  int253 *all[1024];
  int i;

  for (i = 0; i < 1024; i++) {
    all[i] = (int253 *) malloc(sizeof(int253));
  }
  free(all[500]);
  free(all[501]);
  /* HERE */
}
You may express your answers as equations. One product you may want to know is 253 * 4 = 1012.