Components of SIM card, Functioning

Components of SIM card, Functioning


  • In 2021, there were more than 14 billion cellular devices in the world even though there were only seven billion people.
  • The ubiquity of these devices but especially smartphones has come to define the contemporary era together with climate change, antimicrobial resistance, and war.

What is a SIM card?

  • ‘SIM’ stands for ‘subscriber identification module’.
  • Specifically, it is an integrated circuit, or a microchip, that identifies the subscriber on a given network.
  • The SIM card is a subscriber’s ID card in this city.
  • In order for a mobile phone to connect to any cellular network that follows the Global System for Mobile Communications (GSM) standard, a SIM card is mandatory.
  • This relationship is established using a unique authentication key a piece of data that a user needs to ‘unlock’ access to the network.
  • Every SIM card stores this data and it is designed such that the user can’t access it through their phone.
  • SIM cards also store information about its own ID number, the IMSI, the subscriber’s location area identity, a list of preferred networks, emergency numbers, and depending on the space available the subscriber’s contacts and SMS messages.

How does a SIM card work?

  • SIM cards are designed according to the ISO/IEC 7816 international standard maintained by as its name indicates the International Organisation for Standardisation and the International Electrotechnical Commission.
  • It applies to electronic identification cards, including smart cards. In this standard, the card itself consists of the integrated circuit, which is glued to a silicon substrate on the top side.
  • On the other side of the substrate are metal contacts, which form the gold­coloured side of the SIM card.
  • Wires connect the integrated circuit from its bottom side to the metal contacts on the top side, and the contacts interface with the phone’s data connectors.
  • The metal contacts have a segmented appearance.
  • Each segment is called a pin and has a specific purpose.
  • On the network side, the SIM helps a phone establish its place within a cellular network.

How have SIM cards changed?

  • SIM cards are a type of smart card, and the history of smart cards begin in the late 1960s.
  • The size and architecture of this microchip evolved in leaps and bounds in the subsequent decades, following Moore’s law.
  • The SIM card itself evolved according to the standards that defined the networks to which its users wished to connect.

What is an eSIM?

  • Over the years, the SIM card has shrunk from the SIM to the mini SIM to the micro SIM to the nano SIM.
  • The latest on this path is the eSIM, with specifications defined by the GSM Association.
  • In the eSIM paradigm, the SIM software is loaded on to a UICC that is permanently installed in the mobile equipment in the factory itself, that it can’t be removed.
  • An eSIM has two immediate advantages.
  • First, it is considered to be environmentally friendlier than a physical SIM: its reprogrammability means no need for more plastic and metal for a new SIM.
  • Second, if a malicious person gains access to your phone, they won’t be able to separately access the SIM application nor be able to duplicate it.
  • There are also at least two disadvantages.
  • First, in some countries, including the U.S., eSIMs can be programmed by subscribers themselves.
  • But this process might be difficult for those with low digital literacy, such as the elderly.
  • Second, an eSIM can in theory allow network operators to track subscribers’ data, including inside apps on the device, especially in the absence of data privacy laws.

Syllabus: Prelims