The full form of SIM is Subscriber Identity Module or Subscriber Identification Module. It is a portable chip and built-in circuit that stores the International Mobile Subscriber Identity (IMSI) in a highly secure manner. SIM is a smart memory card that enables us to establish a phone call across the globe where the contact network of the user is constant. SIM is generally used on smartphone-operated and controlled GSM networks. It is movable and can be used by a user with any mobile device that supports it.

The first SIM card was made in 1991 by Devrient and Munich smart-card maker Giesecke. The SIM was initially recognized and declared by the European Telecommunication Standards Institute. The SIM card stores a lot of information and also brings essential pieces of data back and forth to the network of customers and holds some of their private and personal data as well. The list of information stored by SIM includes address details, text messages, personal security keys, phone number, data regarding network authorization, and other data.

SIM cards come in different sizes, including standard, micro, nano, and embedded SIMs (eSIMs) . The size of the SIM has evolved over time, with the standard SIM measuring 25x15mm and the eSIM measuring 6x5mm. SIM cards are removable and have anywhere from 32 KB to 128 KB.

In summary, SIM stands for Subscriber Identity Module or Subscriber Identification Module, and it is a portable chip and built-in circuit that stores the International Mobile Subscriber Identity (IMSI) in a highly secure manner. SIM is generally used on smartphone-operated and controlled GSM networks and is movable and can be used by a user with any mobile device that supports it. The SIM card stores a lot of information, including address details, text messages, personal security keys, phone number, data regarding network authorization, and other data. SIM cards come in different sizes, including standard, micro, nano, and embedded SIMs (eSIMs).