Number of processes needed to maximize CPU utilization under I/O wait conditions A computer has 2 GB of RAM of which the operating system occupies 256 MB. The processes 
are all 128 MB (for simplicity) and have the same characteristics. If the goal is 99% CPU 
utilization, what is the maximum I/O wait that can be tolerated?

My professor said that there are 14 processes in the memory before proceeding with the solution. Why are there 14 processes?
You want all processes to fit in memory. If there are $N$ processes, then together with the OS they take up $256+128N$ megabytes. Since there is only room for $2048$ megabytes, we need $256+128N \leq 2048$. Dividing by $128$, this is $N+2 \leq 16$.