1.1 Systems Architecture - CPU Components, Slides of Computer science

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System

architecture The

CPU

1.1 Systems Architecture

CPU

Components

• Explain the role of the following
  • MDR
  • MAR
  • CU
  • Buses

1.1 Systems Architecture

The Arithmetic Logic Unit

• The ALU or Arithmetic Logic Unit performs:
  • Logical operations,
  • shift operations and
  • arithmetic operations

Main

Memory

X = 3 Y = 5

Accumulator

8 ADD X, Y ALU

1.1 Systems Architecture

Memory Address Register

• The MAR holds the address of the current instruction being executed
• The MAR knows the location of the data that needs to be accessed
• It keeps track of where data is located MAR (Memory Address Register)

1.1 Systems Architecture

Memory Data Register

• The MDR holds the actual data that is being stored in RAM
• It acts as a buffer and holds data that is copied from RAM, ready for the CPU to process it MDR (Memory Data Register)

1.1 Systems Architecture

Control Unit

• The control unit coordinates all of the activities taking place within the CPU - Much like the conductor of an

orchestra

1.1 Systems Architecture

Processor registers

PC: Points to the next instruction ALU: Temporarily stores arithmetic and logic results MAR: Stores the address of the data MDR: Stores the actual data CIR (Current Instruction Register): Holds the current instruction to be executed

1.1 Systems Architecture

Buses

• Buses are circuits on the motherboard that connect the CPU to other components.
• There are many buses on the motherboard.
• A bus moves instructions and data around the system.
• The speed of a bus is measured in megahertz (MHz).
• The faster the bus, the faster data is communicated.
• The speed of the motherboard is defined by the bus speed.

1.1 Systems Architecture

Types of bus

• Address bus - this sends information about where data needs to go by sending an address to the memory. The address bus only sends data in one direction - from the CPU to RAM.
• Data bus - this sends data to the memory or receives data from the memory. Data can flow both ways along the data bus.

1.1 Systems Architecture

Task 2:

The CPU is split into two major parts. Two of these parts are the Arithmetic Logic Unit (ALU) and the Control Unit.

1. Describe the purpose of the ALU
2. Describe the purpose of the Control Unit

1.1 Systems Architecture

Exam Question: