Understanding computer architecture

Yesterday i happened to meet my cousin Rohit who is in class 9th.He was very much fascinated to know about computers.We had the following conversation which tested all my understanding of computer architecture.
Rohit- hi bhaiya ,how are u?
Me- i m fine Rohit .So how is your studies going on.
Rohit-it is going on fine. Bhaiya I m really fascinated towards computer but i find it really difficult to understand computer architecture.
Me- what happened what is the problem? I think its very easy.
Rohit-no,last week my teacher explained in the class about computer architecture but i could not understand it at all.Rather i was scared by the use of many technical words like hardware,application,single-tier,multi-tier etc.Bhaiya can you please explain me this concept.
Me-ya sure why not.ok let me start with the basic.
First of all you must understand what is a hardware and what is a software?
Rohit-ya i have some idea about it,but i m not very clear.
Me-ok let me explain.A hardware is something which we can touch like a moniter,keyboard,cpu etc
And a software is something by which we perform a particular task like writing a text document using MS word.
Rohit- Can we give me some more examples
Me-sure.you must be listening to music in your computer using window media player or editing a photo using adobe photo shop.Here media player and adobe photo shop are software and your computer is the hardware.
Rohit -oh then what is computer architecture.
Me-computer architecture is the way in which the hardware and software are arranged to perform a particular task.
Rohit-ok
Me- We have two things, one is data and other is application running on this data.In my previous example the music file is the data and the media player is the application that runs on the data.
Rohit-things are getting clearer now.
Me-Based on this arrangement of hardware and applications we have different type of computer architecture like single-tier,two-tier,three-tier and multi-tier.
Rohit-can you explain me in details?
Me-First of all let me explain what is single-tier architecture.
In a single-tier architecture both the data and application resides on the same machine.
Rohit-ya this is true for every computer.
Me-No,you have only seen personal computer.There are other computers which perform many complex tasks
Rohit-i see.
Me-A single-tier architecture works better only for single users.Multiple users cannot access the same common data.
Rohit-How can we solve this problem?
Me-So we have two-tier architecture.
In a two-tier architecture,the data is kept on a separate machine called server and an instance of application is present in the computer of every users.All the different users are connected by a common network called a LAN.
Rohit-ya,i have seen computer connected through LAN in my school.
Me-ya,you must have used the TELNET server in your school.So, in two-tier system multiple users can access the same data simultaneously.Here the users are called clients and this model is also called client-server model.
Rohit-so two-tier architecture is the best architecture available.
Me-no,there is one major drawback of two-tier architecture.It is very difficult to maintain when the size of network becomes large.Suppose a new version of a software comes then we have to upgrade all the users, which is a big challenge.
Rohit-so, we have three-tier archtecture.
Me- Right.
The three-tier architecture has three parts.In the first part data is kept and it is called data server. Here the application is split into two parts.Thus the first part contains the application called the application server and every users just have the user interface part of the application which is the second part.Generally lot of data transfer takes place between the application part and the data part so both this machines are kept close to each other.Other user are connected to the application and data through internet
Rohit-Does this solve all the problem.
Me-ya to some extent.Here atleast it is not required to upgrade all the users application.The application is kept on a single location which could easily be upgraded.
Rohit-does it have any drawback?
Me- ya it does.In this type of architecture also we face the same problem i.e we need to install and upgrade the user interface in the machines of every users.So we go for multi-tier archtecture.
Rohit-so how does the multi-tier architecture operates.
Me--In multi-tier architecture we are free from the problem of installing the same user interface in the machines of every users.In this architecture any one can access the data and application using any web browser like mozilla or Internet explorer.
Rohit-How is it achieved?
Me-Just like the three-tier architecture here the data server and the application server are kept closer to each other,another machine called the web server is kept between the application server and the users are connected to the web server via internet.
Rohit-What is the use of the web server?
Me-.The main function of the web server is to convert the data from the application server into a format that can be easily understood by anyone using a web browser.So it is not required to install the application in any machines also any new user can access the data with the help of a web browser.This architecture is very easy to maintain and so it is widely used now.
Rohit-i use mozilla.I access a lot of website using it. .
Me-Ya .The best example is the yahoomail which you use to check your mail.
Rohit- Does it have some drawbacks?
Me-Ya,the only drawback here is security.
Data transfer is vulnerable to attacks from hackers.
Rohit- you mean virus,spam.
Me-ya and many other type of attacks which you will learn in due course of time.
Rohit-Is there any solution?
Me- Let me tell you one thing,no network is 100% secured.We can ensure some security by having firewall.
Rohit-What is a firewall?
Me-A firewall is a software and hardware combination which allows only certain data to pass through it.It is just like a check gate which allows only known vehicles to enter.So it gives some security.And there are architectures with firewalls which is known as secured web based architecture.
Rohit-What is its structure?
Me-It is same as multi-tier but here we place a firewall between web server and the users.
Rohit-thanks a lot bhaiya.I think that now i have more knowledge about computer architecture than anyone else in the class.
Me-my pleasure.I hope you score good marks in your exams now.
Rohit-ya,definitely.
Me-ok Rohit you really tested my skills in computer science.It is always easy to understand than to make others understand.See you then.bye
Rohit-bye