How do cookies end up on my hard drive?
After a cookie is transmitted through an HTTP header, it is stored in the memory of your browser. This way the information is quickly and readily available without re-transmission. As we have seen, however, it is possible for the lifetime of a cookie to greatly exceed the amount of time the browser will be open. In such cases, the browser must have a way of saving the cookie when you are not browsing, or when your computer is shut off. The only way the browser can do this is to move the cookies from memory into the hard drive. This way, when you start your browser a few days later, you still have the cookies you had previously. The browser is constantly performing maintenance on its cookies. Every time you open your browser, your cookies are read in from disk, and every time you close your browser, your cookies are re-saved to disk. As a cookie expires, it is discarded from memory and it is no longer saved to the hard drive.
