 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
| ä |
Operating
systems strive to do many things
|
|
|
at
the same time
|
|
|
|
ä |
Run a
user program
|
|
|
|
ä |
Read
from or write to a disk
|
|
|
|
ä |
Print
on a printer
|
|
|
|
ä |
Would
like to keep as many resources busy as
|
|
|
possible
to increase the system’s efficiency
|
|
|
| ä |
Multi-programming
or time-sharing
|
|
|
|
ä |
CPU
switches from program to program
|
|
|
|
ä |
Switch
when
|
|
|
|
ä |
A
time slice (10s or 100s milli-sec pass) or when
|
|
|
a
process does an IO operation
|
|
|
| ä |
Gives
the appearance of concurrency
|
|
|
|
ä |
Many
users feel like they have exclusive access
|
|
|
to the
machine
|
|
|
| ä |
Process
model supports this approach
|
|
