J277.1.1.1IP.revision

J277.1.1.1.The purpose of the CPU

by Mr. Shingari

​1.1.1. Architecture of the CPU

Walt:​

To be able to describe the purpose of the CPU.

To be able to state the function of the CPU (fetch and execute instructions stored in memory).

​Main components of computer

​CPU- Central Processing Unit

​The processor controls all the processing of the computer.  The ‘brains’ of the computer

​Retrieves data/instructions from main memory (fetches).

​Processes data

​Carries out instructions (executes instructions).

Stores data into main memory once executed.

​Fetch-decode -execute cycle

​FETCH – Fetches the next instruction and associated data to be fetched from main memory

​

​DECODE – Interprets the instruction, decodes it.

​

​EXECUTE – Performs the instruction, it executes it.

​Wilf

​You know what is the purpose of the cpu.

​You know what is FDE.

Multiple Choice

The CPU is:

• Control processing unit

• Centralised process unit

• Central process unified

• Central processing unit

Multiple Choice

The processor…

• Carries out instructions

• Is main memory

• Is secondary storage

• Is an input device

Multiple Choice

 The main computer components are:

• Input/Output/CPU/Main memory

• CPU/Main memory/Secondary storage

• Input/Output/CPU/Main memory/Secondary storage

• CPU/Main memory/Secondary storage

​Walt

​To be able to describe the common CPU components and their function.

ALU (Arithmetic Logic Unit)

CU (Control Unit)

Cache

Registers

CPU components

​The main components are called:

Control Unit (CU)

Arithmetic Logic Unit (ALU)

Registers that help carry out the above operations.

Registers are immediate memory, which is very fast temporary memory on the CPU to speed up access.

​ALU

​Arithmetic operations

Addition, subtraction, multiplication and division.

Logical operations

Basic logical operations like AND/OR calculations.

​Control Unit (CU)

​Sends control signals between the different internal components:

Memory Read

Memory Write

Hard Disk Drive Read

I/O Write

​Cache

• ​This is very fast, and usually a very small amount of memory on the processor chip.

• ​As programs are executing, the cache holds commonly used instructions.

• ​There are levels of cache L1 and L2.

• ​L1 is usually smaller but faster.

​Registers

​Registers that help carry out the operations in ALU .

Registers are immediate memory, which is very fast temporary memory on the CPU to speed up access.

​Wilf

​You can explain the purpose of each component of CPU

Multiple Choice

its controls all the processes flowing in and out from the processor

• CU

• ALU

• Registers

• Cache

Multiple Choice

What is more expensive Cache or RAM?

• Cache

• RAM

Multiple Choice

it performs arithmetic operations and logic

• CU

• ALU

• Registers

• Cache

Multiple Choice

The CPU cache stores

• Only instructions
• Word documents
• Frequently accessed data and instructions
• A list of IP addresses

Multiple Choice

A cache makes recently accessed data immediately available to the processor

• true
• FALSE

​CPU registers

​PC (Program Counter)- holds the memory address of the next instruction to be processed

MAR (Memory Address Register)-holds the address (location in memory) of the current instruction or piece of data to be fetched or stored.

MDR (Memory Data Register)- holds data or a program instruction when it is fetched from memory or data that is waiting to be written to memory.

ACC (Accumulator)- stores the results of operations carried out in the ALU are stored.

​Fetch-

​Fetch part of the cycle:

Program counter is incremented for each instruction of the program being executed.

The contents of the Program Counter are put into the MAR (Memory Address Register).

The address is transferred along the address bus to main memory (this address indicates which part of memory to fetch the data/ instructions from.

​The data/instruction that has been addressed is transferred back to the processor along the data bus. This is held in the MDR (Memory Data Register).

​Walt

​To describe the function of registers in the Fetch-Execute cycle

To understand how Fetch – Decode - Execute works in more detail

​Decode/Execute part

it is interpreted to find out what operation need to be performed. The instruction is split into an Op-Code and an Operand.

​

The instruction is then caried out by the ALU (Arithmetic Logic Unit) or control unit.

Multiple Choice

Where are the results of calculations stored?

• Accumulator
• ALU
• MDR
• CIR

Multiple Choice

Which component would calculate the result of 6 * 4?

• Accumulator
• ALU
• Control Unit
• MAR

Multiple Choice

Which is a feature of the address bus

• Transfers addresses 
• Bi-Directional
• Carries control signals
• Transfers Data and Instructions

Multiple Choice

Processor doesn’t do the following

• Process data

• Execute instructions

• Execute data

• Operate in Hz

Multiple Choice

The part of a processor in which instructions are executed is known as?

• Core

• Centre

• Execution

• Instruction centre

Multiple Choice

Retrival practice: What acts as an intermediary between the processor and the main memory?

• Bus

• User

• Cache

• Clock

Multiple Choice

What is held in cache?

• All the programming instructions

• Commonly used instructions and data

• Instructions that have been processed

• Data that hasn’t been used for a long time

Multiple Choice

Which component would perform an operation such as 5+8 ?

• Arithmetic Logic Unit

• Accumulator

• Cache

• Control Unit

Multiple Choice

What is held in ROM?

• Data currently in use

• Bootstrap loader

• Instructions frequently used

• Operating System

Multiple Choice

Which Register is the first to be accessed during the Fetch- Decode- Execute cycle?

• PC

• MAR

• MDR

• CIR

Multiple Choice

What is the purpose of the accumulator?

• To perform arithmetic operations

• To hold the results of a calculation

• To hold the accumulation of instructions that have happened

• To remember the previous instruction being worked on