Page 21 - demo

Program A Run Wait Run Wait

Multiprogramming
Time

(a) Uniprogramming

Program A Run Wait Run Wait

Program B Wait Run Wait Run Wait

Run Run Run Run
Combined Wait Wait
A B A B

Time

(b) Multiprogramming with two programs

 There must be enough memory to hold the OS (resident

monitor) and one user program
Program A Run Wait Run Wait
 When one job needs to wait for I/O, the processor can switch to

the other job, which is likely not waiting for I/O
Program B Wait Run Wait Run Wait

Program C Wait Run Wait Run Wait

Run Run Run Run Run Run
Combined Wait Wait
A B C A B C

Time

(c) Multiprogramming with three programs

Figure 2.5 Multiprogramming Example