Cookies are small pieces of information that are stored in a browser. It keeps track of user preference, like what sites are visited, what keywords are used, among others.

The function setcookie() is used to define a cookie that is to be sent along with HTTP headers. The cookie must be sent prior to any output from the script as is the protocol restriction. After setting the cookies, they can be used when the next page is loaded by using $_COOKIE or $HTTP_COOKIE_VARS arrays.

- The web browser visits a website using the HTTP and then it keeps the track of the identity of the user visiting the web page.

- The cookies of HTTP get stored with the personal information of the user and it doesn’t accept the information. 

- Users accept the cookies as by rejecting all the cookies will load the web page in longer time and it will not be desired by the users. 

- Even if the cookie is being rejected a session cookie is being kept for use as it is the provision given to the web browser to use it. 

- The cookies gets stored temporary basis depending on the user of accepting or rejecting it and it basically saves the session so that the duration of the page load can be reduced.

The storage of cookies on the hard disk depends on OS and the browser. The Netscape navigator on Windows, the file cookies.txt contains all the cookies. The path is :

c:\Program Files\Netscape\Users\username\cookies.txt

The Internet Explorer stores the cookies on a file by name username@website.txt is

c:\Windows\Cookies\username@Website.txt

setcookie('variable','value','time');
variable - name of the cookie variable
value     - value of the cookie variable
time       - expiry time

Example:
<?php
setcookie('Test',$i,time()+3600);
?>
Test - cookie variable name
$i - value of the variable 'Test'
time()+3600 - denotes that the cookie will expire after an one hour

This depends on the user's browser and OS.
In the case of Netscape with Windows OS,all the cookies are stored in a single file called

cookies.txt
c:\Program Files\Netscape\Users\username\cookies.txt
In the case of IE,each cookie is stored in a separate file namely username@website.txt.
c:\Windows\Cookies\username@Website.txt