SIM card

A SIM card (Subscriber Identity Module card) is a small, portable integrated circuit that securely stores the international mobile subscriber identity (IMSI) and related key used to identify and authenticate a subscriber on mobile telephony devices, such as mobile phones and computers. It allows mobile network operators to identify and connect to individual users.

The SIM card also contains other data, such as contact lists, SMS messages, network authorization data, personal security keys, and subscription information. It enables a mobile device to connect to a cellular network and make and receive calls, send and receive text messages, and access mobile data services.

SIM cards are typically removable and transferable between compatible devices, allowing users to easily switch their mobile service and associated number between different phones. Different form factors of SIM cards exist, including full-size, mini-SIM, micro-SIM, and nano-SIM, each progressively smaller in size. Newer devices may also utilize embedded SIMs (eSIMs), which are non-removable chips built directly into the device.

The SIM card plays a crucial role in mobile security by providing a secure element for storing authentication credentials. This makes it an essential component of mobile communications.