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OBJECTIVES :
Identify the components of the central processing unit andhow they work together and interact with memory
Describe how program instructions are executed by thecomputer
Explain how data is represented in the computer
Describe how the computer finds instructions and data
Describe the components of a microcomputer system unitsmotherboard
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THE CPUComplex set of electronic
circuitry
Complex set of electroniccircuitry
Set of electronic circuitrythat executes stored
program instructions
Set of electronic circuitrythat executes stored
program instructions
Control center
Control center
Two parts Control Unit (CU)Arithmetic LogicUnit (ALU)
Two parts Control Unit (CU)Arithmetic LogicUnit (ALU)
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y Long-term storage of memory
y Data not lost when computer shut down
y Examples include hard drive, diskette, DVD-ROM
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Two types of storage:
Primary storage
(memory) Stores data
temporarily
CPU refers to itfor both programinstructions anddata
Secondary storage
Long-termstorage
Stored on externalmedium, such as adisk
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y CPU cannot process data from disk or input device It must first reside in memory
Control unit retrieves data from disk and moves it into
memory
y Items sent to ALU for processing Control unit sends items to ALU, then sends back to
memory after processing
y Data and instructions held in memory until sent to anoutput or storage device or program is shut down
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Central Processing Unit is the core component
of a computer. It executes users instructionsand processes calculations.
Central Processing Unit is the core component
of a computer. It executes users instructionsand processes calculations.
Without the CPU, the devices cannot worktogether and so the computer cannot
function
Without the CPU, the devices cannot worktogether and so the computer cannot
function
Like the chief commander of an army, theCPU controls and co-ordinates various
devices in the computer system.
Like the chief commander of an army, theCPU controls and co-ordinates various
devices in the computer system.
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THERE ARE TWO TYPES OF PROCESSORS
TYPE I - Sockettype
TYPE II - SLOTTYPE
Pin arrangement in theSocket type processor is known as
PinGrid Array (PGA).
Slot type processor is alsoCartridge(SECC)
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CPU is often etched on a chip and is usually
called a microprocessor.
Intel Pentium III
Cyrix II Intel Pentium 4
AMD Athlon XP
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y Central processing unit etched on silicon chip
y Contain tens of millions of tiny transistors
y Key components: Central processing unit
Registers
System clock
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y Computers use the binary system to store and processinformation.
In the binary system, there are only numbers 0 and 1,which are called binary digits.
y Music is stored as a sequence of 1s and 0s in the
computer
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y All sorts of information, such as text,sound and graphics, can be stored asa sequence of binary digits (bit pattern)
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Bit Byte Word Short for binary digit
Two possible values:
0 and 1
Can never be empty
Basic unit for storing data0 means off, 1 means on
A group of 8 bits
Each byte has 256 (28)
possible values
For text, stores onecharacter
Can be letter, digit, orspecial character
Memory and storagedevices measured innumber of bytes
The number of bits theCPU processes as a unit
T
ypically a whole numberof bytes
The larger the word, themore powerful thecomputer
Personal computerstypically 32 or 64 bits inlength
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FETCHINGy The control unit gets the next
program instruction from the mainmemory.
DECODINGy The control unit decodes what the instruction Means
EXECUTING
y The ALU executes arithmetic andlogical instructions. It means that theALU controls and performs the actualoperation on the data.
Program Executions
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y The control unit executes theinstructions, sends control signals toand receive control signals from
peripheral devices.
y In other words, it controls the wholecomputer, and directs the entire system to
carry out instructions.
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Addition, subtraction,
multiplication, divisionArithmeticandLogic Unit
Arithmeticunit
Logic unit
Compare numbers,letters, or special
characters
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y When the control unit and thearithmetic and logic unit operate, theystore the information and instruction
temporarily in registers.
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Before a computer executes instructions, they
are first placed in the main memory.
The diagram shows how the CPUexecutes an instruction :
This is called
MACHINE CYCLE
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y Houses the electronic component of the computersystem
Motherboard
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y Flat circuit board thatholds the computercircuitry Central processing unit
(microprocessor) is mostimportant component
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