Computer: A computer is a system in which Hardware and software components are combined which are integrated together and which will provide many operations and also functionalities to the user.

Hardware means physical resources such as processor, memory, devise, monitor, keyboard, etc. software means it consists of collection of programs and also instructions, which hardware resources use for functioning properly. Working cycle of computer consists of some basic components.

They are Input-Process-Output cycle and these are also known as functional components of the computer. These components needs input, which processes the input and gives the required output. The input devices will take the input from the user, the processing is done by CPU and the output is produced by output devices. The data and instructions are held by memory unit while the processing is done.

What is digital computer mean?

It is defined as a machine that is programmable that will read the binary data which is passed by instructions, and also will process this data which is binary, and a calculated digital output is displayed.

Digital computers works on digital data.

Functional components of digital computer:

It consists of input devices, CPU, ALU, control unit, memory registers, memory and output unit.

Input unit: in this input devices are attached to the computer, the input is taken by these devices and the data is converted into binary bits which is understandable for the computer. Input devices like keyboard, mouse, joystick, scanner, etc comes under input devices.

CPU: the input device will enter the information into the computer, then the processing will be done by the processor. The CPU is the “brain of the computer”, it is called like that because it controls all the operations of the computer system.

The instructions are fetched by the CPU from the memory and then interpretation is done to know what operation is done. The data is also received from the memory if needed. CPU will perform all needed computations and also stores the result and shows it on the output devices. The CPU consists 3 components, they perform different functions

ALU,CU and memory unit.

ALU: ALU is useful for performing many calculations like addition, subtraction, multiplication, division and any logical decisions. Logical decisions means two items are compared to check which data is larger or smaller or equal.

Control unit: this is useful for coordinating and controlling the flow of data in and also out of CPU and it is also useful for controlling all the ALU operations, memory registers and input/output units. The instructions are all carried out which are stored in the program.

The fetched instructions are decoded and interpretation is alos done, and control signals are sent to the input/output devices, this process happens till the operation that is needed is properly done by ALU and memory.

Memory Registers: A register means it is a “temporary memory unit” which is inside the CPU. The data is stored by the registers which are used by the processor directly. There are many sizes of registers, 16bit,32 bit,64bit and many more. Specific functions are done by the CPU that are present in the CPU.

Functions like storing the data, storing the instruction, storing the address of a memory location. And many more. The assembly language programmer uses the user registers for operands storage and results. The main register name is accumulator register which contains the operation operands which are meant to be used in the ALU.

Memory: The memory is useful for storing the data and also instructions that is attached to the CPU is known as internal memory. And this is categorized into many location storages, and each will store the data and instructions. There is a same size for memory locations and also they have an address.

The memory location can be read by any memory location very easily and there is no need to search for the whole memory. When the program execution is done, the data will be copied into the memory and this process continues till the execution ends. The internal memory is also known as Primary memory or main memory.

This memory is also known as RAM (Random Access Memory). The data accessing time is not dependent on the memory’s location. That’s why it is called as RAM (Random Access Memory)

Types of RAM

Computer’s main memory is RAM(Random access memory) and it is accessible directly by the CPU. Read and write operations into the CPU are done by the RAM randomly. RAM’s nature is volatile, when the power is off the information that is stored is gone. The currently processing data which is done by the CPU is stored by the RAM. The programs and data which can be modifiable is stored inside the RAM.

There are two forms of RAM chips:



Static RAM memories contains the circuits which are useful for having the information that is stored it happens till the power is there. This memory will require constant power. Cache memory is built by SRAM memories. these type of memories are known as volatile memories. 

Two inverters will form a latch and the transistors are t1 and t2 which are useful for attaching two bit lines to the latch, the main need of this transistor is that it acts as a switch which are useful for opening and closing and word line will control them and that is under the control of address decoder.

The transistors will be turned off when word line is at level 0 and the information is remained by the latch. If the cell is at 1st stage and if the logic value is 1 at a Point A and 0 at point B. till the word line is not yet activated this state will be retained.

The word line will be activated for the read operation to the address decoder by using the address input. The both of transistors are closed by word lines which are activated. Point A’s and B’s bit values will be able to transmit to their bit lines. At the bit lines end the sense or write circuits will send the result output to the processor.

And the address which is provided to the decoder will activate the word line which is useful for closing the both switches in write operation. The sense or write circuit will provide bit value which is to be written in the cell and bit lines signals are stored inside the cell.

DRAM: the binary information is stored by the DRAM, in the form of electrical signals which are applied to the capacitors. The capacitors which are holding the stored information are lost over a period of time. Capacitors should be charged to have their usage.

DRAM has 5 types:

  1. Asynchronous DRAM: the memory device’s time is asynchronously controlled. The signals are generated by the specialized memory controller circuit.
  2. Synchronous DRAM(SDRAM): the CPU’s clock is synchronized directly with the access speed of RAM’s chips.

When the CPU does expect them to be ready, the CPU’s chips will be ready for performing the operations. At CPU memory bus , these memories are operated without wanting waiting states. SDRAM will be available as SDRAM chips which are modules incorporating. And they will form the module’s capacity.

Double data rate SDRAM (DDR SDRAM): it is very fast and it performs many operations on the signals of the clock on two edges, a standard SDRAM will perform the operations on the clock signal which is a rising edge. The rate of data transfer is double when the transfer of data is done on the clock’s two edges.

4.Rambus DRAM: RDRAM is useful for providing the data of transfer which is of high speed through a narrow memory bus of CPU. And many speed up mechanisms are used by RDRAM, like memory interface synchronous, caching inside the DRAM chips and has a fast timing signals. Its width is about 8 or 9 bits.

5. Cache DRAM(CDRAM): it consists of on-chip cache memory (SRAM) and it is of special type it has a buffer of high speed for the main DRAM.

Output unit: this contains output devices which are connected to the computer. The binary data is converted to the data that is received from the CPU to understandable format for humans. Monitor, printer, plotter are the examples for output devices.

Functional components and interconnection between them:

Input unit is present in the computer which is useful for taking the input from the user, and has a CPU which is used for processing the input/output devices which are useful for displaying the output. A common bus will be there, with which these devices communicate.

A bus is path which is useful for transmission of data and it is made up of collection of wires in the form of electrical signals. And this data is transmitted from one device to another device. There are 3 types of buses, address bus, data bus, and control bus.

The address bus is useful for carrying the location’s address of the instruction and the data. And this data bus is useful for carrying the data from one device to another device. And the control signals are carried out by the control bus. So, this bus is the path for every device to communicate with each and every device that is present in the system for CPU, Main memory, and input/output devices.