Sim card stand for subscriber identification module. its help to communication between mobile & network provider. basically a sim card is a IC (integrated circuit ) The IMSI programmed on the SIM card, is the identity of a subscriber every IMSI is mapped to a mobile number . The SIM card is a tiny, rectangular card found in many mobile phones that as an ID card for your handset. It is usually located behind the battery. Every consumer or user data is held in the small chip, such as an authentication key and network specific information; phone numbers SMS texts dialing number, mobile telephone settings like call forward call bearing call waiting etc. Subscriber information, such as the IMSI (International Mobile Subscriber Identity) and details about the mobile network you use. Also save data customer which is modified by user.
Sim cards operated are varty type voltage voltages for SIM cards: 5 V, 3 V and 1.8 V. its came in market different type memory size like 16kb,32kb,64kb,128kb, and many more