Prerequisite for understanding Architechture

We are completely going to focus on the server which stores our oracle database.The server of which i am talking about is not much different from the computers which you are using right now,it also has hardisk and ram but a larger one in size.

Hardisk and Ram are type of  memory where we can save our data.Difference is Hardisk is Cheap in terms of cost(hence always larger in size than ram),Non volatile and Slow in accessing where as Ram is exactly opposite of it.

Consider your hardisk as your money in bank and ram as money at home.
Money in you bank is more safe than money at home,then why dont we keep all of it in bank?
bcoz its not easily accessible as we need to write a check to retrieve money also its time consuming.This is the exact reason why we use ram,"FOR FASTER ACCESS TO DATA".

Since ram is faster in access then why dont we keep all of our money at home rather than in bank.
lets assume that we always keep our all money at home and not in bank and one night thief robbed my home.Now at this point of time i am left with no money.similarly ram is volatile.when we switch off our computers the data stored in ram is lost and hence we require bank(i.e hardisk) to save our money(i.e data).

You must be thinking that why is this stupid fellow tell all the stuff about hardisk and ram,how is oracle related to it?Its because oracle server's architecture has two parts
1. Oracle Instance:-This resides in ram
2.Oracle Databse:- This resides in hardisk

so basically we are going to study what all changes are going to take place in hardisk and ram of an oracle server.