Building Blocks of a Computer System

A computer System is made up of 3 Basic Building blocks

  1. Memory
  2. CPU
  3. I/O

Buses

The blocks are connected to each other by BUS (Binary Unit System). There are three Types of Buses

Buses – Data is transmitted from one part of a computer to another, connecting all major internal components to the CPU and memory, by the means of Buses. Types:

  1. Data Bus: It carries data among the memory unit, the I/O devices, and the processor.
  2. Address Bus: It carries the address of data (not the actual data) between memory and processor.
  3. Control Bus: It carries control commands from the CPU (and status signals from other devices) in order to control and coordinate all the activities within the computer.

<aside> 💡 Imagine a BUS to be a wire carrying different data.

</aside>

Untitled

Zoom into the CPU

The CPU consists of

  1. Control Unit
  2. Arithmetic and Logic Unit
  3. Registers
  4. Cache

Control Unit - CU

  1. A control unit (CU) handles all processor control signals.
  2. It directs all input and output flow,
  3. It fetches the code for instructions
  4. It controls how data moves around the system.

Arithmetic and Logic Unit - ALU

  1. The arithmetic logic unit handles all the calculations the CPU may need, e.g. Addition, Subtraction, Comparisons.
  2. It performs Logical Operations, Bit Shifting Operations, and Arithmetic Operation.

Registers

  1. Registers are small, very expensive areas in a computer's processor or CPU (Central Processing Unit) that store data.
  2. There are generally 6 types of registers.
    1. Accumulator: Stores the resuls of calculations made by the ALU
    2. Program counter: Stores the address of the Next instructuction. This address is passed to the MAR
    3. Memory Address Register (MAR) : It stores the Memory Addresses of the instructions that need to be RETRIEVED from or STORED in the Memory
    4. Memory Data Register(MDR): It stores
      1. Instructions fetched from memory
      2. Any data that is to be transferred in the Memory
    5. Current Instruction Register (CIR): It stores the most recently fetched instructions while it is waiting to be coded and executed.
    6. Instruction Buffer Register (IBR): The instruction that is not to be executed immediately is placed in the instruction buffer register IBR.

Untitled

Cache

A CPU cache is a small amount of fast, expensive memory that acts as a buffer between the CPU and main memory. It stores data and instructions that are used frequently by the CPU so that it doesn't have to access main memory repeatedly.

Input/Output - I/O

  1. Program or data is read into main memory from the INPUT **device or secondary storage under the control of CPU input instruction.
  2. Output **devices are used to output the information from a computer.

Previous

Computer Organization

Next

Instruction Cycle