1.4 Hardware Components

Hardware & Software (to recap from 1.1)

Definitions: (Key words - in red and their definitions in yellow you need to learn by heart )

• Hardware: Physical components of a computer (something you can touch)

• Software: Programs that run on the computer (you can't hold them in your hand)

  • Systems software: Set of programs needed to control the hardware (Operating System)

  • Applications software: Programs that allows the user to carry out a task or produce something.

Physical & Logical Model

Computer Hardware

What is actually inside a the CPU chip?

Main Memory: (e)

There are 2 types of Memory

• • RAM: ( Random Access Memory, also known as; Immediate Access Store or Primary Memory)

    • Memory in which data is temporarily stored for processing. A temporary (volatile) storage area used to load program instructions and store files currently in use.

  • ROM (Read Only Memory also known as firmware)

    • An integrated circuit programmed with specific data when it is manufactured

    • It is non-Volatile part of the memory that hold special programs to help the computer start up.

    • Contains parts of the BIOS (Basic In Out System)

      • The BIOS checks the hardware is working properly.

      • Runs the Bootstrap program. Which locates the Operating System and loads it into RAM.

      • Known as Booting up the computer

Further Reading:

• • New replacement for BIOS in 2011 (Click here for Story)

  • (not part of syllabus but interesting for the future of your computer)

Processor (or CPU) (a)

• ALU (Arithmetic Logic Unit):

This does all the computer's calculations:

• • Performs arithmetic functions on the data (in Binary)

    • It does all the maths

  • Performs logical operations on the data.

    • (e.g. comparing values <= > etc)

      • •Acts as a gateway to processor;

        • a conduit through which all I/O to computer is done

• Control Unit:

Manages how CPU instructions are carried out.

• • Co-ordinates activities taking place in the CPU

  • Co-ordinates memory and peripherals

Registers: (b)

• A series of special on-chip memory that monitor, store binary data and control the information being Fetched & Executed

1. PC - Program Counter:

   • Holds the memory address of the next instruction to be executed by the program

   • Determines the sequence in which the program instructions are executed

     • It ensures that the CPU always knows where it has reached and is able to resume at the correct point following the execution of an instruction

   • Also known as the Sequence Control Register

2. MAR - Memory Address Register

   • Holds the address of the data or instructions currently being carried out or accessed in the main memory

     • (sent from the above PC)

   • i.e. the address of the data / instruction that has been just been fetched

3. CIR - Current Instruction Register

   • Instructions from memory are placed here so that the contents can be decoded and executed.

     • i.e. It holds the instruction while it is being decoded / executed

   • CIR holds the current instruction in the processor while it is being decoded and executed.

     • This speed of the whole execution process.

     • Because the time needed to access the instruction register is much less than continual checking of the memory location itself.

   • CIR will contain both the Operator and Operand of the current instruction

     • e.g. LDA 1001.

4. MDR - Memory Data Register (also known as buffer register)

   • All instructions and data pass in and out of main memory via MDR

   • The contents (data or instruction) of the address specified in the MAR are copied here

   • e.g. the number to be added or instruction to be carried out.

5. SR - Status Register (also known as Flag Register)

   • The flag register is specially designed to contain all the appropriate 1-bit status flags, which are changed as a result of operations involving the arithmetic and logic unit.

   • It contains 'bits' that are set or cleared based on the result of an instruction.

1. General Purpose Registers (Including the Accumulator)

   • GPRs are used for performing arithmetic functions

   • Some computers have only one, the Accumulator;

     • others have up to 16 general purpose registers.

The Accumulator is used to accumulate; RESULTS

• • • Results of processing operations (answers) are stored here temporarily, before being sent to memory (RAM)

• Click on here for an Animated Model of Register use in the Fetch-Execute Cycle

Buses (C)

Homework

Pre Test Homework (for week ending 26/9/2010)

• Homework 3

1) Complete the poster of the CPU and email to me mr.gazz@gmail.com

2) Components Homework (You will have to revise from your notes)

• There may be access to moe notes and interactive quizes from Wednesday.

Further Reading

• More about RAM

• More about ROM

• More links