why session data store cookies

Yes @Nitin you are right .

Rakesh you need to explain your query whatever you are getting.

Thank you For detail i understand that point now.i have one more question

if cookies is disable by user on browser than where the session store the id and how?

First, please note that session data is not stored in cookies. It's the session Id that is stored in cookies.

This is a very fundamental concept and should be very clear. It is good that such a question came up in your mind.

Note that the http protocol is by definition state-less. What it means is when one cycle of request / response is over, neither client nor server remember about each other. It is as if two people meet every day and forget each other's name overnight and ask it again next day.

So, server creates a new session Id, basically just a new guid and stores it in client cookie. In each of subsequent client / server request / response cycles this cookie is checked. It is this same old currency note torn in half and when matches with other half, smuggled gold can safely be handed over to in our bollywood movies.

When session id matches with one in cookie, server is sure that it is talking to same client it spoke a while ago. Because server only put the cookie there in first place.

Hope you understand.

If not google and you will find better explanations all over the Internet.