Page 34 - DCAP403_Operating System

Unit 2: Operation and Function of Operating System

2.4 Summary Notes

Operating systems may be classified by both how many tasks they can perform
“simultaneously” and by how many users can be using the system “simultaneously”. That
is: single-user or multi-user and single-task or multi-tasking.

A multi-user system must clearly be multi-tasking.
A possible solution to the external fragmentation problem is to permit the logical address
space of a process to be noncontiguous, thus allowing a process to be allocated physical
memory wherever the latter is available.
Physical memory is broken into fixed-sized blocks called frames. Logical memory is also

broken into blocks of the same size called pages.
Memory protection in a paged environment is accomplished by protection bit that are
associated with each frame.
Segmentation is a memory-management scheme that supports this user view of memory.
Segmentation may then cause external fragmentation, when all blocks of free memory are
too small to accommodate a segment.

2.5 Keywords

Clustered System: A clustered system is a group of loosely coupled computers that work together
closely so that in many respects they can be viewed as though they are a single computer.
Distributed System: A distributed system is a computer system in which the resources resides
in separate units connected by a network, but which presents to the user a uniform computing
environment.
Real-time Operating System: A Real-time Operating System (RTOS) is a multitasking operating
system intended for real-time applications. Such applications include embedded systems
(programmable thermostats, household appliance controllers, mobile telephones), industrial
robots, spacecraft, industrial control and scientific research equipment.

2.6 Self Assessment

Fill in the blanks:
1. A ........................ is a program in execution.
2. ........................ is a large array of words or bytes, each with its own address.

3. A ........................ is a collection of related information defined by its creator.
4. A ........................ provides the user with access to the various resources the system
maintains.
5. An RTOS typically has very little user-interface capability, and no ........................ .
6. A ........................ cannot always keep CPU or I10 devices busy at all times.

7. A multiprocessing system is a computer hardware configuration that includes more than
........................ independent processing unit.
8. A ........................ system is a collection of physical interconnected computers.
9. A system task, such as ........................, is also a process.

10. ........................ is achieved through a sequence of reads or writes of specifi c memory
address.

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