Acomputer with a single cpu has 4gb ram, with the operating system taking up 512mb

Let's assume a condition where ram is 256 MB and the program size is more than 256 MB

in that case, CPU has to wait for I/O to load the remaining part of the program..in this case  

CPU utilization is much poorer.

So adding gives benefit only when your CPU is fast enough to take advantage like if a process waiting for I/O

it can put the current process in the run queue and take another process from the ready queue.

This way a better CPU utilization can be achieved.  

So by adding ram we can load more programs while waiting for I/O . CPU utilisation will be better.

here by adding 2GB ram we can load 2048/256 = 8 new process into ram at the same time.

2. if cpu have to execute the cpu bound process that wait for I/O cpu will be idle most of the time while  

waiting for I/O to be done..this way CPU utilization will be  poorer as compare to earlier.