Computer Computer ApplicationsApplicationsComputer Computer

ApplicationsApplications

NCBS Stage 1NCBS Stage 1

The Central Processing Unit Slide 2 Computer Applications Stage 1

Course Content and Assessment

• Practical – 60% (2 Hrs Weekly)– File Management– Internet– Word Processing– Spreadsheets

• Theory – 40% (I Hr Weekly)

The Central Processing Unit Slide 3 Computer Applications Stage 1

The Central Processing Unit

• The ‘brain’ of the computer• A tiny piece of silicon (chip)

containing millions of transistors• Getting smaller, faster and

cheaper all the time

The Central Processing Unit Slide 4 Computer Applications Stage 1

Functions of a Computer• The function of a computer is to

process data• Processing means turning data into

meaningful information

Input (Data in)

Processing (Calculations

etc)

Output(Results of

processing – Information)

Storage of Results

The Central Processing Unit Slide 5 Computer Applications Stage 1

Input

• Data– Raw data is figures etc that can be

manipulated

• Programs– Instructions to the computer about

what to do with the data

The Central Processing Unit Slide 6 Computer Applications Stage 1

Input devices

• Used to put data and programs into the computer– keyboard, disk, microphone,

scanner etc

The Central Processing Unit Slide 7 Computer Applications Stage 1

Processing

Means turning raw data into meaningful information

MathematicalOperati

ons

1+1=2

Logical Operations

A=6

B=4

Logical deduction

A>B

The Central Processing Unit Slide 8 Computer Applications Stage 1

Processing• Takes place in the CPU

• Main Memory holds the data and instructions that are being used

• Processing needs both the CPU and Memory

CPU

Memory

The Central Processing Unit Slide 9 Computer Applications Stage 1

Output

• The results of processing need to be output for user to see and use

The Central Processing Unit Slide 10 Computer Applications Stage 1

Output can be sent to ….

• Screen• Disk (floppy, zip, CD, DVD

etc)• Printer• To another computer via a

network

The Central Processing Unit Slide 11 Computer Applications Stage 1

The Parts of the CPU

These parts make up the CPU

Control Unit

ALU

Registers

• Control unit• Arithmetic/Logic

Unit• Registers

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The Control Unit

• This controls everything that happens inside the computer

• It transfers data and program instructions between the Memory and the ALU

• It sends the results back to Memory and later to a storage device

The Central Processing Unit Slide 13 Computer Applications Stage 1

The Arithmetic/Logic Unit (ALU)…

• Performs either mathematical or logical operations– Addition, subtraction,

multiplication etc– Greater than, less than etc

• The ALU produces results

The Central Processing Unit Slide 14 Computer Applications Stage 1

Registers…

•Are temporary storage areas for data and/or instructions

•Data, instructions and results are held in registers for a very short time

•They are faster than RAM so they speed up processing

•Areas in the ALU and CU

The Central Processing Unit Slide 15 Computer Applications Stage 1

Main Memory

CPU

Memory

•Main Memory is made up of RAM and ROM and is not part of the CPU

•Data passes in and out of RAM to be processed

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Storage

• Anything stored in RAM is only held there temporarily - until processing is complete

• Permanent storage is called Secondary Storage

• This is needed or work would be lost as soon as the computer was switched off

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Storage Devices

• Disks• CDs• DVDs• Paper

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Memory v Storage• Memory or Main Memory is the

term used for temporary storage ie RAM and is outside the CPU

• Registers are a type of Main Memory found in the CPU

• Secondary storage covers a lot of devices used for files such as disks, CDs etc

The Central Processing Unit Slide 19 Computer Applications Stage 1

Programs

• Programs are sets of instructions for the computer to follow

• The program must be in Memory (RAM) before processing can take place

The Central Processing Unit Slide 20 Computer Applications Stage 1

Executing/Running a Program

The program must be placed in Main MemoryThe data must be placed in Main Memory

The Central Processing Unit Slide 21 Computer Applications Stage 1

Running a Program

Once the program and data are in place the following sequence is followed:

CPU

Memory

1.1. FetchingFetching2.2. DecodingDecoding3.3. ExecutingExecuting4.4. StoringStoring

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CONTROL UNIT ALU

Registers

Fetching Instructions

The control unit fetches (gets) the instruction from memory.

Memory

The Central Processing Unit Slide 23 Computer Applications Stage 1

Decoding Instructions

• The control unit decodes the instruction

• It then moves the necessary data from Memory to the ALU for processing

CONTROL UNIT ALU

Registers

Memory

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Executing Arithmetic/Logic

OperationsThe ALU performs the arithmetic or logical operation on the dataAll processing takes place in the ALU

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Storing Results

The ALU stores the result of its operation on the data in Memory or in a Register until they are output to a storage device

Control

Unit

ALU

Registers

MEMORY

The Central Processing Unit Slide 26 Computer Applications Stage 1

The Machine Cycle

• This is the time taken by the CPU to process a single program instruction

• The time is divided into 2 phases– I-time and– E-time

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(I-time) Instruction Time

The time it takes the Control Unit to fetch an instruction from Memory and decode it is called instruction time

+Memory

Control Unit ALU

Memory

Control Unit

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(E-time) Execution Time

The time it takes to carry out an ALU operation and then store the result is called execution time

+

ALU

Memory

ALU

Registers

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Computer Speed• Computers carry out millions of

instructions per second (MIPS) • Processors are described in

MegaHertz (MHz) and GigaHertz (GHz)

• These figures indicate how quickly the computer can process instructions

The Central Processing Unit Slide 30 Computer Applications Stage 1

Conclusion and Key Words

• CPU• ALU• Registers• Control Unit• Main Memory• RAM• Data

• Information• Program• Secondary

storage• Machine Cycle• I-time• E-time

The Central Processing Unit Slide 31 Computer Applications Stage 1

References

Computing Essentials 2005By Timothy and Linda O’Leary

Computers - Tools for an Information AgeBy H L Capron - Ch 3

Computing in the Information AgeBy Stern and Stern - Ch 4