What type of memory does a SIM card contain essential information about the subscriber?

A SIM card contains essential information about the subscriber stored in non-volatile memory. This type of memory retains information even when the power is turned off, which is crucial for functions such as maintaining subscriber identity, authentication keys, and service-related information.

In contrast, volatile memory would lose its data when powered down, making it unsuitable for storing subscriber information that needs to persist across device shutdowns. Therefore, non-volatile memory is specifically designed to hold essential data securely over time, ensuring continuous accessibility whenever the SIM card is in use.

While the choice of both volatile and non-volatile suggests the capability of containing data in different states, the primary function of a SIM card relies solely on its non-volatile attributes to preserve critical subscriber information.