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.
