What primary function does a subscriber identity module (SIM) serve?

The primary function of a subscriber identity module (SIM) is to authenticate a user on a mobile network. This process involves verifying the identity of the subscriber by using the unique International Mobile Subscriber Identity (IMSI) stored on the SIM card. When a mobile device connects to a network, the SIM allows it to establish a secure link and communicate with the network infrastructure, thereby enabling the user to access network services, make calls, send texts, and use mobile data.

In addition to authentication, the SIM also plays a role in securing the connection and may store additional information such as network-related settings and encryption keys, but its essential purpose is to confirm the identity of the user and facilitate their access to the mobile network.