What is a SIM card?

SIM card is the abbreviation of the initials of subscriber identity module. \ x0d \ x0d \ SIM card is also called subscriber identity card and smart card. GSM digital mobile phone can only use this card. \ x0d \ x0d \ subscriber identity module (SIM), commonly known as "SIM card", is a smart card, which is mainly used to store user identification data, short message data and telephone numbers. \ x0d \ x0d \ SIM card is mainly used for GSM network, W-CDMA network and TD-SCDMA network, but the compatible module can also be used for IDEN telephone. Some people refer to the RUIM card and UIM card of CDMA2000 and cdmaOne, also called SIM card. Although they have similar functions and abide by all the same mechanical and electrical standards and some software standards, the upper applications are not necessarily compatible. \ x0d \ x0d \ sim consists of CPU, ROM, RAM, EEPROM and I/O circuit. When users use SIM, in fact, the mobile phone sends commands to the SIM card, and the SIM card should be executed or rejected according to the standard specification; SIM card is not a simple information memory.