Page 38 - DCAP104_EXPOSURE_TO_COMPUTER_DISCPLINES

Unit 2: Data Processing

Notes
Distributed caching uses caches spread across different networked hosts, e.g.
Corelli

2.6.3 The Difference Between Buffer and Cache

The terms “buffer” and “cache” are not mutually exclusive and the functions are frequently
combined; however, there is a difference in intent.

A buffer is a temporary memory location, that is traditionally used because CPU instructions
cannot directly address data stored in peripheral devices. Thus, addressable memory is used
as intermediate stage. Additionally such a buffer may be feasible when a large block of data is
assembled or disassembled (as required by a storage device), or when data may be delivered
in a different order than that in which it is produced. Also a whole buffer of data is usually
transferred sequentially (for example to hard disk), so buffering itself sometimes increases transfer
performance or reduce the variation or jitter of the transfer’s latency as opposed to caching where
the intent is to reduce the latency. These benefits are present even if the buffered data are written
to the buffer once and read from the buffer once.
A cache also increases transfer performance. A part of the increase similarly comes from
the possibility that multiple small transfers will combine into one large block. But the main
performance-gain occurs because there is a good chance that the same datum will be read from
cache multiple times, or that written data will soon be read. A cache’s sole purpose is to reduce
accesses to the underlying slower storage. Cache is also usually an abstraction layer that is designed
to be invisible from the perspective of neighbouring layers.

2.7 Summary

• Data processing consists of those activities which are necessary to transform data into
information.

• OP code (operation code) is the portion of a machine language instruction that specifies is
to be performed by the C.P.U.

• Computer memory is basically divided into two type: primary and secondary memory.
• Processor register is a small amount of storage available on the C.P.U. can be accessed more
quickly than storage available.
• Data bus carries the data between the different components of the computer.

2.8 Keywords

Computer Bus: Computer Bus is an electrical pathway through which the processor
communicates with the internal and external devices attached to the computer.
Data Processing System: A group of interrelated components that seeks the attainment of a
common goal by accepting inputs and producing outputs in an organised process.

Draw flow of Data Processing Activities.

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