> For the complete documentation index, see [llms.txt](https://sim-cards.learn-telecom.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://sim-cards.learn-telecom.com/gsm-identifiers/sim-subscriber-identity-module.md).

# SIM - Subscriber Identity Module

A Subscriber Identity Module (SIM) card is a small electronic chip that is used to identify and authenticate a mobile device on a cellular network. 

It is inserted into the device and contains information such as the phone number, the International Mobile Subscriber Identity (IMSI), and the Authentication Key (Ki).

The SIM card consists of a small microcontroller, non-volatile memory, and other passive components. The microcontroller is responsible for managing the SIM's functionality and communication with the mobile device. 

The non-volatile memory stores the data and information that is needed for the SIM card to operate.