What is the full form of SIM? Or What does SIM stand for?

Sim card is a small electronic chip with the mobile network operator’s details embedded, e,g ICCID, IMSI, etc. The full form of the sim or SIM stands for is the subscriber identity module. A GSM mobile device uses a sim card to provide voice and other services, while a CDMA phone does not need any external chip.

The full form says that it is a module with identifies. The global identity is the IMSI. It comes in many sizes, e.g., Standard, Macro, and Nano.

At the start of the gsm network, the sim card was bigger in size, and mobile devices too. Now with the more compact devices, sim size also reduces. There are nano and macro sim cards with smaller sizes. Sim has inbuilt memory to store text, contexts, etc., and small executable programs called applets. In-memory stores following.

Text messages. 
Phone Contacts.
Authentication Keys
Applets  and other data.

IMSI and SIM :

A sim is nothing without an identity. IMSI assigned by the mobile operator to the sim card.  Which is a unique global identifier? Each mobile operator has a range of IMSIs.  Another essential thing sim stores are authentication keys. Keys are used for generating authentication vectors at the time of a SIM registration and may be on-call setup.  The communication over the radio channel is encrypted used authentication vectors for security.


A sim may have multiple IMISs. A roaming sim is one of the examples of a multi-IMSI SIM card. Based on the roaming location, a particular IMSI gets active.

Along with IMSI, ICCID is another unique identifier for the module. A standard body assigns the ICCID number. Unlike the former, the latter is printed on the chip.

eSIM or embedded sim:

ESIM is similar to a SIM functionally, but it is embedded in the phone hardware.  Each sim may have multiple IMSIs. All should be preconfigured to get low-cost roaming.  But this requires putting a very high number of IMSIs in the SIM at the time of manufacturing, covering all, is practically impossible as the chip has limited memory.  This limits the low-cost roaming options for the roaming sim card providers. eSIM is an option, where a sim card is loaded with IMSIs over the air.

Apple is one of the device manufacturers that has launched the phone with eSIM. With eSim, any IMSI can be provisioned by the mobile operator while roaming. This enables the support of a very high number of identities and no change in the chip when changing mobile operators.

SIM and CDMA :

CDMA is another network for mobile communication similar to GSM.  But it is less in use. In CDMA, there is no sim card. All information is present in the device for network operations.  This leads to a severe issue when someone wants to change the phone but not the phone number.