Question

A computer with a single cpu has 4gb ram, with the operating system taking up 512mb and each user program also taking up 256mb. suppose now that the computer system must execute i/o bound processes that wait for i/o 95% of the time. what is the benefit of adding 2gb ram to the computer system in terms of cpu utilization? what happens if the computer system must execute cpu bound processes that wait for i/o 12% of the time?

Answer 1

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.