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Central Processing Unit Part I. Bayram G üzer. Central Processing Unit. Central processing unit is a control center that converts data input to information output. It includes complex set of electronic circuit components. It executes stored program instructions

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Central Processing Unit Part I

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Central Processing UnitPart I

Bayram Güzer


Central Processing Unit

  • Central processing unit is a control center that converts data input to information output.

    • It includes complex set of electronic circuit components.

    • It executes stored program instructions

  • Central processing unit consist of two main parts;

    • Control unit

    • Arithmetic logic unit


Central Processing Unit

  • CPU interacts closely with memory (primary storage).

  • Memory often regarded in the context of the central processing unit however it is not part of the CPU, it is a seperate piece of unit.


Central Processing Unit

  • Memory holds the data temporarily at the time the computer is executing a program.

  • Secondary storage holds permanent or semipermanent data on some external medium until it is needed for processing.


Control Unit

  • The control unit contains circuit components that uses electrical signals to direct the entire computer system to execute stored program instructions.

    • Like the orchestra leader

    • It doesn’t execute program instructions but it directs other parts of the system to do so.

    • It communicates with both arithmetic/logic unit (ALU) and memory.


Arithmetic/Logic Unit (ALU)

  • The ALU contains the electronic circuit components that executes all arithmetic and logical operations.

  • ALU performs four kinds of arithmetic operations;

    • Addition

    • Subtraction

    • Multiplication

    • Division


Arithmetic/Logic Unit (ALU)

  • Logical operation is usually a comparison. The unit can compare;

    • Numbers

    • Letters

    • Special characters

  • Logical operations can test three conditions

    • Equal to, less than and greater than condition.


Arithmetic/Logic Unit (ALU)

  • Equal-to condition

    • Compares two values to determine if they are equal

  • Less-than condition

    • Compares two values to determine if one is less than another

  • Greater-than condition

    • Compares two values to determine if one is greater than another.


Arithmetic/Logic Unit (ALU)

  • Combined conditions

    • Less-than or equal to

      • Checks to find if one value is less than or equal to the other value.

    • Greater-than or equal to

      • Checks to find if one value is greater than or equal to the other value

    • Not equal to (literally sometimes referred as greater than or less than)

      • Checks to find if one value is not equal to the other value


Arithmetic/Logic Unit (ALU)

  • Relational operators are the symbols which lets you define the type of comparison you want the computer to perform


Registers

  • Registers are special-purpose, high-speed, temporary storage areas for instructions of data.

    • Not part of memory

    • Special additional storage locations

    • High-speed access is available

  • Registers work under the direction of the control unit

    • To accept, hold, and transfer instructions or data

    • To Keep track of where the next instruction to be executed or needed data is stored


Registers

  • Some of the register types are;

    • Address register: keep track of where a given instruction or piece of data is stored in memory.

    • Storage register: temporary holds data taken from or about to be sent to memory.

    • Accumulator: collects the results of computations.

    • There are other types of registers which is used for several functions as well.


Memory

  • It is also known as primary storage and main memory

    • Often expressed as random-access memory (RAM)

    • Not part of the CPU

  • Memory stores program instructions or data as long as it is in the operation and has not been terminated.

  • The CPU cannot process data from an input device or disk directly, therefore the data must first be available in memory.

  • Control unit is responsible from;

    • Receiving the items from memory

    • Sending the items from memory

    • Transferring the items from memory to secondary storage.


Memory

  • It is also known as primary storage and main memory

    • Often expressed as random-access memory (RAM)

    • Not part of the CPU

  • Memory stores program instructions or data as long as it is in the operation and has not been terminated.

  • The CPU cannot process data from an input device or disk directly, therefore the data must first be available in memory.


How the CPU Executes Instructions

  • Before an instruction can be executed, program instructions and data must be placed into memory from an input device or a secondary storage.

Control Unit

ALU

3

2

Decode

Execute

1

Fetch

4

I-Time

E-Time

Store

Memory


How the CPU Executes Instructions

  • Instruction has been executed in 4 different steps;

    • Fetch

    • Decode

    • Execute

    • Store

Control Unit

ALU

3

2

Decode

Execute

1

Fetch

4

I-Time

E-Time

Store

Memory


How the CPU Executes Instructions

  • Fetch: The control unit gets the instruction from the memory

  • Decode: The control unit decodes the instruction and directs the necessary data to be moved from memory to the ALU.

  • The first two steps are together are called as instruction time (I-time)

Control Unit

ALU

3

2

Decode

Execute

1

Fetch

4

I-Time

E-Time

Store

Memory


How the CPU Executes Instructions

  • Execute: The arithmetic logic unit executes the arithmetic or logical instructions by performing the actual operations on real data.

  • Store: The arithmetic logic unit stores the result of this operation in memory or in a register.

  • Step 3 and 4 together are called as execution time (E-time).

  • The combination of I-time and E-time is called as machine cycle.

Control Unit

ALU

3

2

Decode

Execute

1

Fetch

4

I-Time

E-Time

Store

Memory


How the CPU Executes Instructions

  • Each central processing unit has an internal clock that produces pulses at a fixed rate to synchronize all computer operations.

  • Pulses are electronic signals like heart beat, clock beat, or school ring.

Control Unit

ALU

3

2

Decode

Execute

1

Fetch

4

I-Time

E-Time

Store

Memory


How the CPU Executes Instructions

  • Clock pulse has two stage;

    • high voltage (like a tick sound) - ON

    • Low voltage (like a tock sound) - OFF

  • Clock tells circuits when to start sending data on wires and when not to sent data on wires.

Control Unit

ALU

3

2

Decode

Execute

1

Fetch

4

I-Time

E-Time

Store

Memory


How the CPU Executes Instructions

  • Instruction set is a specific group of instructions which each type of CPU is designed to understand.

Control Unit

ALU

3

2

Decode

Execute

1

Fetch

4

I-Time

E-Time

Store

Memory


How the CPU Executes Instructions

  • SET TOTAL TO 0

  • ADD NEXT NUMBER TO TOTAL DATA:88

  • ADD NEXT NUMBER TO TOTAL DATA: 76


How the CPU Executes Instructions

  • Fetch: fetch the instruction from the memory

  • Decode: control unit determines that addition must take place and gives instructions for the next number

  • Execute: ALU does the addition, increasing the total to 164

  • Store: ALU stores the new total in the register and removes old value in the register.


How Control Unit Finds Instructions and Data

  • Each memory location has identified by an address

    • A unique number, much like a mailbox

  • Each memory location may contain only one instruction or piece of data

    • When data is written back to memory, previous contents of that address are destroyed

  • Each address is referred to by number but

    • Programming languages use a symbolic (named) address, such as Hours or Salary


References

  • Capron, H. L. (2000). Computers Tools for an Information Age.(6th ed.). New Jersey, USA: Prentice Hall.

  • http://homepage.cs.uri.edu/faculty/wolfe/book/Readings/Reading04.htm

  • http://en.wikipedia.org/wiki/Pulse_%28signal_processing%29

  • http://www.yale.edu/pclt/PCHW/clockidea.htm

  • http://www.camiresearch.com/Data_Com_Basics/data_com_tutorial.html

  • http://en.wikipedia.org/w/index.php?title=Relational_operator


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