Block diagram of cpu | What is the between cpu and memory?

Block diagram of cpu | What is the between cpu and memory?


          Input Unit: Input unit acts as medium between the user and the computer. This unit contains devices through which the user enters data into computer. The input devices translate the human being information into the form understandable by computer.

          CPU (Central Processing Unit) : CPU is considered as the brain of the computer. It performs all types of data processing operations. It stores data, intermediate results
and instructions (program). It controls the operations of all parts of computer.

          ALU (Arithmetic logic Unit : This unit performs All arithmetic operations like addition, subtraction, multiplication division and the logical operations like decision making and performing logical or, logical and, and logical not operations.

CPU consists of three components namely
          Memory Unit: It is used to store and retrieve the data, results and programs
          Control Unit: To control the operations of input unit, output unit, ALU and memory.
          Output unit : output unit acts as medium between the computer and the user.
This unit contains devices through which the computer sends the results and information to the user. The output devices translate the computer`s  output into the form understandable by users.


 All types of computers perform five basic operations for converting raw input data into information useful to their users with the help of CPU.
1. Accepting data and instructions from the outside world into the computer through input unit.
 2. Saving and retrieving data and instructions as and when required from the memory unit.
3. Performing arithmetic, logical operations on data in order to convert them into useful information with the help of ALU.
4. Producing useful information or results for the user, such as a printed report or visual display by sending it to output unit.
5. Controlling the order of all the above operations and to decide when and how to perform all these operations.


CPU stands for central processing unit. It is the combination of three units, namely Memory or Storage Unit, Control Unit and ALU (Arithmetic Logic Unit).
CPU acts as the brain of the computer. It performs all types of data processing operations like storing data, intermediate result and instructions (program). It also controls the operations of all parts of computer.

Now let us see in detail how the individual parts of the CPU does the jobs.

          Memory or Storage Unit : This unit can store instructions, data and intermediate results. This unit supplies information to the other units of the computer when needed. It is also known as internal storage unit or main memory or primary storage or random access memory (RAM). Its size affects speed, power and capability of the computer.
There are two types of memories - primary memory and secondary memory. The main functions of memory unit are
  • Storing all the data to be processed and the instructions required for processing.
  • Storing intermediate results of processing.
  • Storing final results of processing before these results are passed to an output device.
  • Transmitting all inputs and outputs.

          Control Unit : This unit controls the operations of all parts of computer. The main functions of control unit are
Controlling the transfer of data and instructions among other units of a computer. Managing and coordinating all the units of the computer. Obtaining the instructions from the memory, interprets them and directs the operation of the computer  Communicating with input/output devices for transfer of data or results from storage. It does not perform any data processing or data storing operations. But it makes other devices to do these operations.
          ALU(Arithmetic Logic Unit): This unit consists of two subsections namely. Arithmetic section logic section. The functions of these two sections are as given below
          Arithmetic Section: Performs arithmetic operations like addition, subtraction, multiplication and division. All complex operations are done by making repetitive use of these basic operations only.
          Logic Section: Performs logic operations such as comparing, selecting, matching and merging of data.

Function of computer memory

A memory is just like a human brain. It is used to store data and instructions. Computer memory is the storage space in computer where data is to be processed and instructions required for processing are stored.

The memory is divided into large number of small parts. Each part is called a cell. Each location or cell has a unique address, which varies from zero to memory size minus one.

For example, if computer has 128k words, then this memory unit has 128 1024 = 131072 memory location. The address of these locations varies from O to 131071 Memory is primarily of three types

  • Cache Memory
  • Primary Memory or Main Memory
  • Secondary Memory 
          Cache Memory: Cache memory is a very high speed semiconductor memory, which can speed up CPU. It acts as the CPU and main memory. It is used to hold those parts of data and program which are most frequently used by CPU. The parts of data and programs are transferred from disk to cache memory by operating system, from where CPU can access them.

  1. Stores data and programs for temporary use
  2. Reduces program execution time
  3. Reduces access time
  4. Faster than main memory
  1. Expensive
  2. Its capacity is limited
          Primary Memory (Main Memory): Primary memory holds only those data and instructions on which computer is currently working. It has limited capacity and volatile
in nature, i.e. data gets lost when power is switched off.

 It is generally made up of  device. these memories are not fast as registers. The data and instructions required to be processed earlier reside in main memory. It is divided into two subcategories - RAM and ROM.

      Characteristics of Main Memory
  • These are semiconductor memories.
  • Usually volatile in nature, Hence data is lost in case power is switched off.
  • It is working memory of the computer.
  • Faster than secondary memory.
  • A computer cannot run without primary memory.

           Secondary Memory (External Memory): It is a non-volatile memory. Hence contents will not be lost when the power goes off. It is slower than main memory. These are used for storing Data/Information permanently.
CPU directly does not access these memories, instead they are accessed via input-output routines. Contents of secondary memories are first transferred to main memory and then CPU can acces it.

Examples of secondary memories are Hard Disks, Flash Drives, CD-ROM, DVD, etc.

          Characteristics of Secondary Memory are
These are magnetic and optical memories.
It is known as backup memory.
It is non-volatile memory. Hence data is permanently stored even if power is switched off.
It is used for storage of the data and programs in the computer. Computer may run without secondary memory.
Slower than primary memories.

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