1. Basics of Operating Systems
: Concept of Spooling and Buffering
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2. Recap
In the last class, you have learnt about
• Various Operating Systems
• Single User Operating Systems
• Multi-User Operating Systems
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3. Objectives
On completion of this period, you would be able to
know
• Spooling
• Buffering
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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
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5. Spooling
Disk
I/O
Online
CPU
Card Reader Line Printer

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
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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
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8. What is a Buffer ?
A buffer is an area of main memory for holding
data during input and output data transfers
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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
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10. 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
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12. Output Buffering
• Processor stores the data in a buffer
• Output device takes the data from the buffer
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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
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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
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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
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16. Frequently Asked Questions
1. Define the terms Spooling and Buffering
2. Explain in detail Spooling and Buffering
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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
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