With the wide spread usage mobile phones, almost all users of mobile phones can identify a SIM which is inserted into the phone, which allow one to start telecommunication. But do all of them know what is carried inside a SIM?  How does it connect you? I doubt at least, three in a crowd of four will not know and most will not mind not knowing as long as they can make calls and send text messages…

This article will let us learn some important things about SIM cards that you use in your daily life.

It stands for Subscriber Identity Module. It can be regarded as an integrated circuit or a smartcard which mainly holds IMSI (International Mobile Subscriber Identity) and Authentication Key (related to security), but there are some other information stored in a SIM. The following table illustrates what a wealth of information is contained in a SIM.

You might have already seen that a SIM circuit is embedded into a plastic card. SIM is the integrated circuit embedded in this card. This is called the "SIM card" and it can be transferred between different mobile devices.

There are different sizes of SIMs. The one you use in your mobile phone is called the mini SIM. If you use a tab with 3G technology, sometimes you can’t use your mobile phone’s SIM with it as the slot is smaller than that; hence you need a micro SIM. The different sizes of SIMs are illustrated in the following figure:

Note: FF stands for FORM FACTOR

European Telecommunications Standards Institute introduced the concept of SIM parallel to the GSM technology. The first ever SIM card was made in 1991 by a Munich smart-card maker Giesecke & Devrient, and the first 300 SIM cards were sold to a Finnish wireless network operator Radiolinja.

Since SIM is a part of the GSM technology, and your knowledge on SIMs will be incomplete without knowledge on GSM. It stands for Global System for Mobile communication. It is also called the 2G (2nd Generation) technology of telecommunication. I think you have heard of 3G and 4G more than GSM during the past couple of years, due to various promotion campaigns conducted by service providers. GSM technology is the predecessor of 3G and 3G is a later evolution of GSM.

GSM is a set of technologies and protocols that enables digital communication across several different platforms. Before GSM, the world of mobile communication was ruled by the 1G technology, known commonly as the Analog Technology!

A GSM network has 4 main stakeholders.

1. Base Station System
2. Network and Switching System
3. General Packet Radio Service (GPRS) System
4. Operations Support System.

I think this article helped you to gain a basic knowledge of the SIM that makes you connected to the world! Without him, I think many of you will not survive these days!

References:
[1] http://www.ebay.com/gds/SIM-Card-Guide-/10000000177629426/g.html
[2] http://en.wikipedia.org/wiki/Subscriber_identity_module
[3] http://gadgets.ndtv.com/mobiles/news/cutting-a-sim-micro-sim-into-a-nano-sim-may-be-possible-after-all-268925
[4] http://en.wikipedia.org/wiki/GSM