Operating System - Properties
Batch processing
Batch processing is a technique in which an Operating System
collects the programs and data together in a batch before processing starts. An
operating system does the following activities related to batch processing −
· The
OS defines a job which has predefined sequence of commands, programs and data
as a single unit.
· The
OS keeps a number a jobs in memory and executes them without any manual
information.
· Jobs
are processed in the order of submission, i.e., first come first served
fashion.
· When
a job completes its execution, its memory is released and the output for the
job gets copied into an output spool for later printing or processing.
Advantages
· Batch
processing takes much of the work of the operator to the computer.
· Increased
performance as a new job get started as soon as the previous job is finished,
without any manual intervention.
Disadvantages
- Difficult to
debug program.
- A job could
enter an infinite loop.
- Due to lack of
protection scheme, one batch job can affect pending jobs.
Multitasking
Multitasking is when multiple jobs are executed by the CPU
simultaneously by switching between them. Switches occur so frequently that the
users may interact with each program while it is running. An OS does the
following activities related to multitasking −
· The
user gives instructions to the operating system or to a program directly, and
receives an immediate response.
· The
OS handles multitasking in the way that it can handle multiple
operations/executes multiple programs at a time.
· Multitasking
Operating Systems are also known as Time-sharing systems.
· These
Operating Systems were developed to provide interactive use of a computer
system at a reasonable cost.
· A
time-shared operating system uses the concept of CPU scheduling and
multiprogramming to provide each user with a small portion of a time-shared
CPU.
· Each
user has at least one separate program in memory.
· A
program that is loaded into memory and is executing is commonly referred to as
a process.
· When
a process executes, it typically executes for only a very short time before it
either finishes or needs to perform I/O.
· Since
interactive I/O typically runs at slower speeds, it may take a long time to
complete. During this time, a CPU can be utilized by another process.
· The
operating system allows the users to share the computer simultaneously. Since
each action or command in a time-shared system tends to be short, only a little
CPU time is needed for each user.
· As
the system switches CPU rapidly from one user/program to the next, each user is
given the impression that he/she has his/her own CPU, whereas actually one CPU
is being shared among many users.
Multiprogramming
Sharing the processor, when two or more programs reside in
memory at the same time, is referred as multiprogramming. Multiprogramming
assumes a single shared processor. Multiprogramming increases CPU utilization
by organizing jobs so that the CPU always has one to execute.
The following figure shows the memory layout for a
multiprogramming system.
An OS does the following activities related to multiprogramming.
· The
operating system keeps several jobs in memory at a time.
· This
set of jobs is a subset of the jobs kept in the job pool.
· The
operating system picks and begins to execute one of the jobs in the memory.
· Multiprogramming
operating systems monitor the state of all active programs and system resources
using memory management programs to ensures that the CPU is never idle, unless
there are no jobs to process.
Advantages
- High and
efficient CPU utilization.
- User feels
that many programs are allotted CPU almost simultaneously.
Disadvantages
- CPU scheduling
is required.
- To accommodate
many jobs in memory, memory management is required.
Interactivity
Interactivity refers to the ability of users to interact with a
computer system. An Operating system does the following activities related to
interactivity −
- Provides the
user an interface to interact with the system.
- Manages input
devices to take inputs from the user. For example, keyboard.
- Manages output
devices to show outputs to the user. For example, Monitor.
The response time of the OS needs to be short, since the user
submits and waits for the result.
Real Time System
Real-time systems are usually dedicated, embedded systems. An
operating system does the following activities related to real-time system
activity.
- In such
systems, Operating Systems typically read from and react to sensor data.
- The Operating
system must guarantee response to events within fixed periods of time to
ensure correct performance.
Distributed Environment
A distributed environment refers to multiple independent CPUs or
processors in a computer system. An operating system does the following
activities related to distributed environment −
· The
OS distributes computation logics among several physical processors.
· The
processors do not share memory or a clock. Instead, each processor has its own
local memory.
· The
OS manages the communications between the processors. They communicate with
each other through various communication lines.
Spooling
Spooling is an acronym for simultaneous peripheral operations on
line. Spooling refers to putting data of various I/O jobs in a buffer. This
buffer is a special area in memory or hard disk which is accessible to I/O
devices.
An operating system does the following activities related to
distributed environment −
· Handles
I/O device data spooling as devices have different data access rates.
· Maintains
the spooling buffer which provides a waiting station where data can rest while
the slower device catches up.
· Maintains
parallel computation because of spooling process as a computer can perform I/O
in parallel fashion. It becomes possible to have the computer read data from a
tape, write data to disk and to write out to a tape printer while it is doing
its computing task.
Advantages
- The spooling
operation uses a disk as a very large buffer.
- Spooling is
capable of overlapping I/O operation for one job with processor operations
for another job.
