SIM card is a chip with microprocessor, which contains five modules, and each module corresponds to a function: CPU, program storage ROM, working storage ram, data storage EEPROM and serial communication unit. These five modules are integrated in an integrated circuit. Working mode: In working mode, information transmission is completed by mobile phone. Idle mode: In idle mode, all relevant data will be retained, supporting full sleep, instruction sleep or clock sleep, effectively saving electricity.

SIM card has a long history of birth and has been widely used in the era of functional machines. The size of the early SIM card was 25mm× 15mm, and it was usually called a big card or a standard card.

In 2003, the European Telecommunications Standards Institute introduced a smaller MicroSIM card with the size of 12mm× 15mm, commonly known as "small card". However, due to user habits, no mobile phone manufacturers and operators followed this standard at that time. It was not until 20 10 that iPhone4 adopted this SIM card slot for the first time, which promoted the popularization of the new SIM card standard with the help of Apple's influence.

After using two generations of microSIM cards for iPhone, the SIM card standard supported by iPhone5 has become an updated NanoSIM card, also known as "Micro Card", with the size of 12.3mm×8.8mm, which is the smallest mobile phone card so far. Of course, calories and MicroSIM cards can also be cut into the size of NanoSIM cards with a card cutter. With the popularity of micro-cards, most flagship mobile phones support NanoSIM cards.

Will the SIM card disappear?

Apple, which has spared no effort in the innovation of SIM card, wants to completely make the SIM physical card disappear. In recent years, an "eSIM card" has appeared. Its characteristics are that it does not need a card slot and is pre-installed in the mobile phone; Different operator services can be switched through the system interface. In fact, this technology has been adopted in iPad ADAIR 2 and iPadmini34G versions, but because most operators around the world have not followed up, these two tablets still retain physical card slots.

Related protocols followed by SIM card.

ж16: the smart card standard stipulates the process and rules of data exchange between all touch-type IC cards and card readers, and stipulates the electrical and physical characteristics of IC cards.

ETSITS102.221:UICC-terminal interface; Physical and logical characteristics

GSM protocol

3 gppts11.11:specifies the data interaction process and rules between the SIM card and the mobile phone, specifies the file system of the SIM card, and specifies the electrical and physical characteristics of the SIM card.

3gppts11.14: specifies the interaction flow between SIMSTK function and mobile phone.

USIM protocol: 3gppts 3 1. 102: characteristics of universal subscription mode (USIM) application.

User information in SIM card

The SIM card contains all the information belonging to the user. It is a "smart" card conforming to GSM standard, which contains information related to users and is stored in the client, including:

A. authentication and encryption information ki (one of the input parameters of KC algorithm, key number);

B. International Mobile Subscriber Number (IMSI);

C, a3: imsi authentication algorithm;

D, A5: encryption key generation algorithm;

E, A8: Algorithm for generating user key (Kc) before generating key (Kc).

F. Call prohibition information and dial reduction information. In addition, for network operation, SIM should also be able to store some temporary data, namely temporary mobile station identification number (TMSI), area identification number (LAI) and key (Kc).