Computer is an electronic device that performs calcul;ation on data, manipulates the data band thus presenting the results to humans.
The computer includes not only the hardware but also software that are neccessary to make the computer functional.
Like any other system , computer is also a system which communicates with all its functional units.
All the functional units work together to get input. Then input is processed and output is genrated. Functional units or computer organisition are explained below:-
Computer Organistion:
A computer performs basically five major operations or functions. These are:

This is the process of entering data and programs into computer system. .
You should know that computer is an electronic machine like any other machine which takes input raw data and performs some processing giving processed data or output.
Thus, the input unit takes data from human or other systems, it consists of instructions regarding what to do.
The process of saving data and instructions permanentally known as storage.
Data has to be fed into the system before the actual processing starts. It is because the processing speed of CPU is very fast that data has to be provided to CPU with the same speed.
Therefore the data is first stored in the storage unit for fast access and processing.
The storage unit performs the following major functions:-
All data and instructions are stored here before and after processing.
Intermediate results of processing are also stored here.
The task of performing operations like arithmetic and logical operations is called processing.
CPU takes data and instructions from the storage unit and does all sorts of calculation based on the instructions given and the type of data provided.
It is then sent back to the storage unit.
This is the process of producing results from the data for getting useful information.
Similarly the output produced by the computer after processing must also be kept somewhere inside the computer before being given to you in human readable form.
Again the output is also stored inside the computer. it may also be used for further processing.
The manner in which instructions are executed and operations are performed.
Controlling of all operations like input, processing and output are performed by control unit.
It takes care of step by step processing of all operations inside the computer.
In order to carry out the operations mentioned above, the computer allocate the task between its various functional units, the computer system is divided into several units for its operations:
CPU: The place from where everything is done, decisions are made, computations are performed, and input/output requests are delegated.
Memory: Stores information being processed by the CPU.
Input devices: Allow people to supply information to computer system.
Output devices: Allow people to recieve information from computer system.
Buses: A bus is a subsystem that transfers data or power between computer components inside a computer.
What happens when you turn on a computer?:
The process of starting a computer and loading the operating system is referred to as "Booting".
To boot a computer is to load an operating system into computer's main memory or random acess memory(RAM). Once the operating system is loaded, it is ready for users to run applications.
Operating system generally does the following when you switch on the computer system:-
A soon as the computer is turned on, the basic input/output system (BIOS) on your system's read only memory(ROM) chip is "woken up" and take charge. BIOS is already loaded because it is built into the ROM chip and unlike Random Access Memory(RAM), ROM contents don't get erased when the computer is turned off.
BIOS first does a power-on self test(POST) to make sure that all the computer's components are operational. Then the BIOS's boot program looks for the special bot programs that will actually load the operating system on to hard disk.
First, it looks for drives at the specific places where operating system is located. If there is a diskette in drive A but it's not a system disk, BIOS will send you a message that drive A doesn't contain a system disk. If there is no diskette in drive A, BIOs looks for the system files at a specific place on your hard drive.
Having identified the drive wher boot files are located, BIOS next looks at the first sector and copies information from it into specific locations in RAM.
It then loads the boot record into a specific place in RAM.
The boot record contains a program that BIOS now branches to, giving the boot record control of the computer.
The boot record loads the initial system file(for example, in DOS system) into RAM from diskette or harddisk.
The initial file then loads the rest of the operating system into RAM.
The initial file loads a system file that knows how to work with the BIOS.
One of the first Operating system files that is loaded, is a system configuration file, information the configuration files tells the loading program which specific operating system files need to be loaded. For example, specific device driver
Another special file that is loaded is one that tells which specific applications or commands the user wants to have included or performed as part of the boot process. In DOS, this file is named AUTOEXEC.BAT. In windows, It is called WIN.IN
After all operating system files have been loaded, the operating system is given control of the computer and performs requested commands and then waits for the first interactive user input.
Thus You have seen that the various subparts of a computer system work together, Thus it is known as a machine or system.

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