System Architecture - Components of the CPU & The Fetch Decode Execute Cycle Flashcards

1
Q

What is the Purpose of the Processor?

A
  • The processor is “the brains of a Computer System”
  • It Processes Data
  • It retrieves Data/Instructions from Main Memory (Fetch)
  • Carries out instructions (Executes Them)
  • Stores Data into Main Memory once Executed
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2
Q

Summarise the Fetch-Execute-Decode cycle.

A
  • The processor checks the Program Counter (PC) to see what instruction to run
  • An instruction is fetched from memory
  • The instruction is transferred to the MDR
  • The instruction is then decoded in the Control Unit
  • The decoded instruction is then executed in the ALU
  • The program counter is incremented
  • The cycle is repeated
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3
Q

In detail, what happens during the ‘Fetch’ part of the Fetch-Execute-Decode cycle?

A
  • The Program counter is incremented by 1
  • The contents of the Program Counter are put into the MAR (Memory Address Register)
  • The address stored in the Memory Address Register is transferred along the Address Bus to Main Memory
  • The instruction / data stored in this memory location is transferred back to the processor along the data bus
  • The instruction or data is copied to the MDR (Memory Data Register)
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4
Q

In detail, what happens during the ‘execute-decode’ part of the Fetch-Execute-Decode cycle?

A
  • The instruction in the Memory Data Register (MDR) is decoded by the Control Unit (CU)
  • CU to be decoded is stored in the Current Instruction Register (CIR)
  • The Program Counter (PC) is incremented by 1
  • The instruction the the CIR is decoded by the
  • The calculation instruction are carried out by the ALU (Arithmetic Logic Unit)
  • Results of calculations are placed into the Accumulator
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5
Q

What is the function of the Control Unit?

A
  • The Control Unit (CU) Decodes instructions
  • It sends out signals to control the flow of data inside the CPU
  • It sends out signals to control the flow of data outside the CPU (main memory / input devices / output devices)
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6
Q

What is the function of the Arithmetic Logic Unit (ALU)?

A

The ALU performs all the arithmetic calculations (e.g. addition, multiplication, division) and logical comparisons (e.g. greater than, equal to, AND, OR, NOT)

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7
Q

What is the function of the Accumulator?

A

The Accumulator holds the results of any arithmetic or logical calculations performed by the ALU

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8
Q

What is the function of the Program Counter (PC)?

A

The Program Counter stores the location of the next instruction/data address to be executed

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9
Q

What is the function of the MAR (Memory Address Register)?

A

The MAR holds the memory address of the data or instruction that the CPU is about to use

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10
Q

What is the function of the MDR (Memory Data Register) ?

A

The MDR Stores the data that has been fetched from the main memory, or data that is waiting to be transferred to the main memory

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11
Q

What is the function of the CIR (Current Instruction Register)?

A
  • The CIR stores the most recent instruction that has been fetched from memory.
  • The instruction is stored in the CIR while it is waiting to be executed
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12
Q

What is transferred down the data bus?

A

Data and Instructions

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13
Q

What carries the next instruction that will be fetched?

A

Address Bus

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14
Q

What component of the CPU sends signals such as “I/O Read”

A

Control Unit

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15
Q

What component of the CPU would perform an operation such as 5+8?

A

Arithmetic Logic Unit

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16
Q

What component of the CPU would would send a signal such as “Memory Read”?

A

Control Unit

17
Q

What component of the CPU would perform an operation including the word “And”?

A

Arithmetic Logic Unit

18
Q

Which register holds the number of the current instruction being worked on?

A

Program Counter

19
Q

Which register holds the instruction/data temporarily after it is brought to the processor from the main memory?

A

Memory Data Register

20
Q

Which register holds the results of calculations?

A

Accumulator

21
Q

Which register holds the address of the next instruction?

A

Memory Address Register

22
Q
A