Working of a ComputerAuthor : Pandu Ranga Rao N
E - Mail :

Its all like Human body!!!...

You may directly answer to this question by saying that a computer works only if Windows is present in the computer or something like that. I am not saying that you are totally wrong. It is Windows that made your system to work, but, how? When you call up some hardware engineer for some problems in your system, he will ask for Driver software etc. Why? For knowing why, you must need to know how computer works, which means working mechanism of a computer.

Its like our stomatch! : Actual computer!...

We are all knows that, normally a computer makes use of software to interact with the hardware to bring some desired output. These softwares are nothing but, programs which in turn consists of set of instructions. An instruction is a code word for performing some action inside a computer.

Organs and external parts of our body !!!...

Apart from external devices, which one can see externally, such as key board, mouse, monitor, printers and more, a computer has internal devices. These internal devices are housed inside the system box which is actually the computer itself.

Heart and Brain inside a computer !!!...

The main device or part is perhaps the CPU. CPU stands for Central Processing Unit and is responsible for overall functioning of other computer components. Various calculations are performed in the CPU. Apart from performing calculations, CPU also directs various internal devices to perform some action based on the instruction given in the program.

Where does the food stay in our body temporarily???...

One may ask now, where do the program stay. For that, I need to explore you now to the world of memory devices. If you ask me generally what Memory devices store, then I will be happy to answer directly, the instructions and the data which we provide to the computer, based on which an action is being performed.

Types of remembrance

The world of memory devices are of two types, out of which the first one will be called as Primary Memory and the second one is known as Secondary Memory.

Store temporarily VS permenently

Data and programs gets stored in these memory types, provided, the contents in the primary memory gets erased automatically, when the computer gets turned off. The contents in the secondary memory will remain as it is, even if the power goes off.

Forget bad experiences in life : It's RAM !!!....

There is only one device which falls under the primary memory category and it is called as RAM (Random Access Memory, some pupil call it as Read Write Access Memory, but, that’s not so popular among techies). This memory is made with many Integrated Circuit (IC) chips which are mounted on a single Printed Circuit Board (PCB). The unit will be mounted on a slot meant for it on the motherboard. The basic function of RAM is to store data and programs which are currently being executed.

Store good memorable experiences in life : its hard disk !!!...

While it is only the RAM which is falling under Primary Memory category, the secondary memory category has got a vast range of devices. The devices range from ROM to a Hard Disk to a Mobile storage known as Micro SD cards. ROM stands for Read Only Memory, which is used to store data and programs which are a part of a common startup routine which brings in actual life to a computer system. Actually, various devices attached to the computer get activated and gets life when the programs inside the ROM gets executed. These collective programs are known as BIOS which stands for Basic Input Output System (BIOS). They are popularly known as BIOS routines.

Remember to do daily common actiivities : Its ROM !!!...

The ROM is a secondary memory which has got subtypes. The subtypes are EPROM, EEPROM. Both EPROM and EEPROM are also ROM except that it is erasable and rewritable in nature. The memory can be erased by using a burner. One should place the unit inside the burner and switch on the power supply. The burning process will erase the contents inside the EPROM. Once erased, the EPROM becomes unusable until one loads some programs and data in it.

Know the internal structure of your permenent storage, how it is made, etc..

The next device which falls under the secondary devices is a Hard Disk. A hard disk is made of round platter, which is mounted on a spindle, inside a rectangular box. The structure of a hard disk resembles our old friend “Gramophone recorder” which was a popular device during 1950’s which was used for recording and playing music. Similar to the gramophone recorder, a hard disk has a head which is used to read and write data from and in to the round platter. A hard disk can store voluminous information in it. While EPROM, EEROM can store only a few Mega Bytes of data in it, a hard disk can store several Tera Bytes (TB) of information in it. In future, the storage sizes can reach several Yotta Bytes (YB).

Brain is located inside the skull of our head, is it not? similar way...

Present popular devices such as CD’s, DVD’s, Blu–Ray disks, Pen drives and several other Micro SD cards do come under secondary storage devices. They store at present, data ranging from several MB’s to several GB’s. The hard disk will be fixed inside the CPU Box and will be considered as internal storage device. The other devices will be considered as external storage devices.

How we do certain actions : Its Program execution !!!...

The programs and data are stored inside the Hard disk. They will be copied on to the RAM for execution purposes when a user requests the program to be executed. Program execution means performing some action based on instructed to do so, by the instructions given in the program.

When we wake up from our bed, what we do ? : Its similar story here !!!...

When the computer gets powered ON, the processor gets initialized and enters into a self test. This routine is well known as Power On Self Test (POST). During this test, the various motherboard components such as DMA controller, Programmable Peripheral Interface, Programmable Interrupt Controller gets tested. The POST routine then transfers its control to BIOS, which initializes basic input/output (I/O) devices. The Basic I/O devices are Keyboard and Monitor. The basic I/O devices should work in order for the computer to work further. The working of computer will come to a stand-still when there is malfunctioning of any of the two devices.

The BIOS will transfer its control to the OS Loader, which is normally located at the first sector of the Hard Disk. If the required OS loader is not located at the first sector, the BIOS gives out an error message, as “Please insert bootable disk and press enter key to continue” or similar message and halts there itself.

If there is an OS Loader, the execution control will be handed over to the OS Loader and OS Loader will load the OS which was installed by the user or by the system’s engineer. The control of execution will be handed over to the OS, once loaded and launched successfully.

The third party devices such as Mouse, sound card, printers, USB and also any other devices gets loaded during the startup routine of the Operating System. Once loaded successfully, the OS will wait for user to give commands to perform some action. From now on, it is the responsibility of the user to launch programs of his choice, in order to work with the computer.

What we do, when some one instruct us to bring something from shop??, its similar story here!!!...

When the user gives some command, the command interpreter will look for the existence of that command and also the type of it. There are two types of commands available, namely, internal and external commands. Internal commands are embedded inside the OS capsule. The external commands are commands originated from user applications or are some programs supplied with the operating system.

Whenever the command is given, OS checks in its command vocabulary. If it finds it there, loads appropriate instructions to execute the command. If does not find in the set, checks in the folders which are preset by the path variable or any other similar settings. If it finds the program file which is meant to run the command, loads the program file in the memory and executes instructions which are found inside the program file.

Author : Pandu Ranga Rao N
E - Mail :
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