SIM Full Form

The full form of SIM refers to a Subscriber Identity Module or Subscriber Identification Module.

It is formed of an integrated circuit that helps in storing the international mobile subscriber identity (IMSI) number and its related key and is used to identify and authenticate subscribers of the mobile devices. 

SIM Full Form

This article contains the full form of SIM and a summary about it. 

SIM cards are always used on GSM phones. There are certain types of phones such as CDMA, TDMA, and AMPS that do not use a SIM as the required data is programmed directly into the phone.

The circuits in the physical smart card, SIM, forms the part of a universal integrated circuit card.SIM card is made up of PVC with contacts and semiconductors embedded within it. The first UICC smart cards were similar to the size of bank cards; sizes were reduced gradually over the years.

The first SIM card was developed by Munich smart-card maker Giesecke & Devrient in 1991. The SIM got its first specification by European Telecommunication Standards Institute.

A SIM Card Contains the following: 

  • Unique serial number (ICCID),
  • International mobile subscriber identity (IMSI) number, 
  • Security authentication and ciphering information,
  • Temporary information related to the local network, 
  • Two passwords: a personal identification number (PIN) for protecting data, and personal unblocking code (PUC) for PIN unlocking. 

SIM cards store SMS messages and the user’s contacts. 

Up to 250 name/number pairs and up to 50 SMS text messages can be stored in SIM cards.

Replaceable SIM cards have four standard sizes:

  • Full-size – 85.6mm × 53.98mm × 0.76 mm
  • Mini-SIM – 25mm x 15mm x 0.76mm
  • Micro-SIM -15mm x 12mm x 0.76mm
  • Nano-SIM -12.3mm × 8.8mm × 0.67mm

The eSIM or Embedded SIM, an irremovable one comes in one size:

6mm x 5mm x <1mm

A phone without a SIM is like a body without a soul. Without a SIM card, mobile won’t be able to connect to any mobile network. Various SIM cards can hold a different amount of data ranging between 16 and 64K. It can hold

  • Cell phone number
  • Rate plan
  • LAI (Location Area Identity)
  • Service features and preferences
  • Text messages
  • Address book (info for about 250 contacts)
  • PIN lock

Working of a SIM Card

  • The phone obtains and relays the IMSI from SIM card to the network.
  • The network looks up the IMSI in its internal database for the IMSI and checks its known authentication key.
  • The network generates a random integer and signs it with the authentication key to create a new number. This number is the response it uses to check if the SIM card is legitimate.
  • The phone receives the random integer from the network and forwards it to the SIM which signs it with its authentication key to create a new number. This number is sent to the network.
  • If the generated number sent by the network and the SIM card matches, then the SIM card is declared legitimate and access is given.

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