CPU Organisation

Introduction

• CPU organization is the arrangement of CPU components in systematic order to work efficiently.

Characteristics

• As we know that a computer manipulates data according to the given instructions using stored program concept. Here, stored program concept means the program and data are stored in the same memory unit.
• The central processing unit(CPU), performs the bulk of the data processing operations.

Architecture/Structure [Click this link for Details]

• A typical CPU consists of two parts that operate at the same time.
  • Bus Interface Unit(BIU) :

• • Execution Unint(EU) :

• Besides the above three major architecture, CPU organisation also includes –  (a) Instruction Organisation (b) Micro-Operation Organisation (c) Data Path/Bus (d) Memory Unit Organisation

Data Path/ Data Bus

• Data path or Bus is used to connect the components of the computer with each other to move or transfer data, information, signals, addresses etc. from one location/component to another component. 
• The speed of a bus is measured in megahertz (MHz). 

Types of Data path or Bus :

(A) On the basis of data path working location, they are –

• • Internal Data Paths:

    • These paths are useful for moving the data between two registers or between a register and ALU.
    • They are located within CPU/Processor i.e. these data paths connect the components of CPU with register.
    • They transfer data or signals within the CPU i.e. from register to register.

  • External Data Paths:

    • The roles of these data paths are normally to link the CPU registers with the memory or I/O interfaces. This role is normally fulfilled by the system bus.
    • They transfer data or signals within the system i.e. from register to memory or register to IO Interfaces.
    • They are spread throughout the computer system.

  (B) On the basis of type of carrying data by a data bus, they are –

• • System Bus/Local Bus

    • The system bus connects the CPU, memory, and the input/output devices directly.
    • System bus is a single computer bus that transmits and shares data, address and signal throughout the computer and between associated devices. 
    • It carries data, address, and control information with very fast speed.
    • The speed of the system bus plays a major role in the performance of a computer system besides CPU and memory.
    • It is primary bus service to process information.

  • Control Bus

    • Control bus carries control signals/clock’s pulses from the processor to other associated components of the computer system.
    • The flow of control bus is unidirectional.

  • Address Bus

    • Address bus carries memory addresses(location of particular memory) from the processor to other components of the computer system such as primary storage and input/output devices.
    • The address bus flow is unidirectional .

  • Data Bus

    • Data bus carries the data from the processor to other components(main memory) of the computer system and its vice-versa.
    • The data bus flow is bidirectional .