What is SIM Card and Everything You Should Know Abou It

By Carrie Tsai,  Last Updated: August 26, 2019

In the era of mobile internet, no one can live without a smartphone. But however well the performance of your phone is, without a SIM card, it will end up as a device that can only play video or play games with Wi-Fi. It can neither make a phone call nor sent messages.

So it is obvious that without the SIM card, our life will become boring and inconvenient.

What is SIM Card

Is the SIM card just a mental piece that can store phone numbers? Of course not, the full name of it is Subscribe Identity Module. Since it is basically in the form of card from its emergence to the present so it is also called SIM card.

In fact, it is much more than storing phone numbers. It is a chip with a microprocessor and there is a CPU in it. In addition to that, it also has program processor ROM, RAM, data storage EEPROM and many serial communication units.

In this sense, it looks like a microcomputer. When we are using the mobile phone, the phone will send instructions to the SIM card and it will execute under the standard set by the operator and then feedback to the mobile phone.

If you take a careful look on it, you will find that this small piece of mental is divided into many different ares by black lines, which may be similar to a spider.

Connection point with mobile phone varies according to different area, and the functions will differ, too. For instance, some will reset the SIM card and some will exchange data, some represent the power(Vcc), clock(CLK), programming voltage(VPP) and data I/O port(Data).

What Does a SIM Card do

After the instruction of the SIM card, you may also concern about the use of SIM card in our daily life. And let’s take a look at it.

1. PIN code protection

The information of the mobile phone user, the encrypted key and user’s contacts are stored in the chip, which can be authenticated by the GSM network client identity and encrypt the voice information of user during a call.

So even if SIM card is removed and installed in other phones, the money in the Alipay and bank card can be prevented from being stolen, mainly relying on the PIN code protection from SIM card. After setting, users need to input the correct PIN code when restarting the phone, inserting  SIM card so that the SIM card can function normally.

2. User identity authentication

To confirm whether the user identity is legal, only by verifying the authentication key of the SIM card, the right of accessing the webpage and making the call can be determined.

Simply, put, when we are using mobile phone to make a call or access to the internet, the SIM Card will plays a role of verification permission and the impact on the signal is very small.

3. Store user related data

The data stored by the SIM Card can be divided into 4 categories. The first is fixed storage data, including International Mobile Subscriber Identity(IMSI), Authentication Key (KI), etc.

The second is temporary data storage of network, such as Location Area Identifier(LAI), Mobile Subscriber Temporary Identification Code(TMSI), public telephone network code forbidden access, etc.

Another is related service codes, such as personal identification number(PIN) and unlock code(PUK), the billing rate, etc. The forth involves the telephone directory, which is the telephone number input by users.

4. Voice information protection

The SIM Card itself has a security algorithm that is able to encrypt the voice information of the user during the call.

How to Install a SIM Card

In the main, SIM Card can be divided into 4 sizes: Standard SIM, Mini SIM, Micro SIM and Nano SIM.

There are mainly two design of inserting SIM Card.

If your phone’s battery is able to be disassembled, then you will can put off the back cover of your phone to insert the SIM Card. Just need to overlap the mental part of SIM Card with that of card slot. In order to help installation, the card is designed with a gap for better identification.

Please note that Apple and some new-release Android phones support the Nano SIM Card, while other Android phones mainly support Mini or Micro SIM Card. Given the varying size of SIM Card, the installing method may differ, too.

But the basic steps of inserting SIM card is similar and simple.

The card slot will be placed outside the smartphone. And you will notice that a pinout for retrieving card will be attached in the box when you purchase a new smartphone. When you have it stabbed, the card holder will pop up automatically. Then, just insert the SIM Card into the card slot and put it into the original place.

If your SIM Card is standard or mini one, there is a need to cut the card to fit into the nano size for iPhone or new Android phones. In addition, you should also pay attention to whether the thickness of the card is flat with the card slot. If not, it may be hard to put it right into the phone. Or you can use some tool like knife to polish the card.

If you do not have a Nano SIM Card, it is advisable replace your card with a new one in service hall.

The above is the things you should know about SIM card, hopefully it can serve as an helping hand for you.