SIM card

Brain of the mobile phone

Have you ever checked your parents' or elder siblings' mobile phones? When you are checking them, have you ever noticed that you need a SIM card to use the phone? If not, there'll be an error message saying 'Insert SIM'. So, we can call the SIM card the brain of the mobile phone, since it carries all the data needed for the operation of the phone.

From a scientific perspective(point of view), a SIM card is a small computer in a mobile phone. A SIM (Subscriber Identity Module) card available today can store between 16 KB and 64 KB in its memory. We can store hundreds of telephone numbers, short messages and other data in it. These other data includes the data regarding identifying the user. It also includes information about the package that the subscriber is using.

This SIM card includes data about the telephone network. So, you can easily identify where this phone is kept, using Location Area Identity (LAI). When you switch it on, the SIM will start a search to find LAI.

The other most important thing in a SIM card is the IMSI (International Mobile Subscriber Identity) number. GSM (Global System for Mobile Communications) and UMTS (Universal Mobile Telecommunications System) mobile networks have this IMSI number. It varies in each and every SIM card. This number includes 15 digits.

All this data will be stored in a small microprocessor in the SIM card. This microprocessor connects with the mobile phone using the metal contacts.

The glossy copper or brass metal part of a SIM card is known as this contact. These SIM cards are used not only to get information from the mobile networks. In July 2005, the Finland government had introduced an electronic identity card using SIM cards.

This was known as a citizen certificate and had included private information about the user. It can be read through a computer or a PDA (Personal Digital Assistant).