1

Basics of Operating Systems

: Concept of Spooling and Buffering

2

Recap

In the last class, you have learnt about

• Various Operating Systems

• Single User Operating Systems

• Multi-User Operating Systems

3

Objectives

On completion of this period, you would be able to know

• Spooling

• Buffering

4

Spooling

• SPOOL : Simultaneous Peripheral Operation On-Line

• A spool is a buffer that holds output for a device, such

as a printer, that cannot accept interleaved data streams

• Spooling overlaps input of one job with the

computation of other jobs

• The spooler may be reading the input of one job while

printing the output of a different job as shown in next

slide

I/O

CPU

Line PrinterCard Reader

Online

Disk

Spooling

6

Spooling Technique

• A high speed device like a disk is interposed

between a running program and a low speed device

involved with the program input/output

• Communication between a high speed device and

low speed device is isolated

• High speed device transfers the data to the spool

• Low speed device gets the data from the spool

7

Advantages

• Performance of the system is increased

• CPU and I/O devices work more efficiently

• Leads naturally to multiprogramming

• Also used for processing data at remote sites

8

What is a Buffer ?

A buffer is an area of main memory for holding

data during input and output data transfers

9

Buffering

• Overlaps the I/O of job with that of its own

computation

• After the data have been read and the CPU is

about to start the operation, the input device is

instructed to begin the next input operation

• Both the CPU and I/O device are busy

Buffering

11

Buffering

• By the time CPU is ready for next operation, the input device would have finished reading it

• CPU creates data and puts into a buffer until an output device can accept it

12

Output Buffering

• Processor stores the data in a buffer

• Output device takes the data from the buffer

13

Input Buffering

• Data transferred by an input channel is stored in the buffer

• After the data transfer, the processor access the data from the buffer

14

Why Buffering ?

Because of three reasons… • To cope with a speed mismatch between the

producer and consumers of a data streams

• To adopt between devices that have different data-transfer sizes

• To support copy semantics for application I/O

15

Summary

• Spool: Simultaneous Peripheral Operation On-Line

• Spooling overlaps the I/O of one job with the computation

of another job

• A high speed device like a disk is interposed between a

running program and a low speed device

• Buffer is an area of main memory, which is used to store

data temporarily during input and output data transfers

• Spooling and buffering increases the system performance

16

Frequently Asked Questions

1. Define the terms Spooling and Buffering

2. Explain in detail Spooling and Buffering

17

Quiz

1. Buffering overlaps the I/O of a job with its own computation

• True • False

2. SPOOL stands for simultaneous peripheral operation off line

• True• False

18

Click here to see•Operating Systems •Basics of Operating Systems •Definition of Operating Systems

•Other subject materials• Web designing

• Micro processors

• C++ tutorials

• java

home