Most of us don’t give much thought to sim cards. For the most part, it is simply a tiny piece of plastic with a chip that helps us to receive and dial phone calls. But they are an interesting piece of technology. Did you know that “SIM” is a short form and not the actual name of the card? Well in this article we shall dive into some interesting facts, history, and working of them.
What is a sim card?
The term SIM stands for Subscriber Identity Module. The cards themselves are plain pieces of plastic with chips attached to them, much like those used in credit cards. They have processor and memory circuits that enable them to hold up to 256 KB of digital data.
Your device already has the hardware such as Antina lines etc needed for telecommunication. SIM cards act as a brain that gives life to this system. They help the telecommunication operator to calculate your usage and hence charge subscribers based on their usage.
Essentially the chip present on your sim card contains some unique code which we will soon discuss. Those codes are what help the network provider to identify you from millions of other sim cards operated by the company.
Unique identification of your sim card
To make sure that you are charged based on what you use your sim card comes with two unique codes. These codes help the telecom provider track your usage. This first unique code is IMSI. It stands for international mobile subscriber identity. The second one is MSISDN which is a short form of Mobile Station International Subscriber Directory Number. It’s nothing but your phone number.
IMSI number is stored as a 64-bit number on the chip. Also with this, there is another 128-bit number [key] which is stored. IMSI along with this key acts as a user ID and password to keep your communication secure and private.
Along with these, other unique numbers come with your sim card. ICCID is short for integrated circuit card identifier. This is an 18 to 22-digit code that gives information about the manufacturing, mobile operator company, service provider network, etc.
Keeping your SIM secure
Did you know that just the way we enable pin for our phones you can indeed do the same with your sim card? You can add a 4-digit pin to your card and hence even if your card is stolen the thief will need this pin to make calls from their phone. Usually, the default pin is 0000, also it might be printed in the envelope which you get along with your card.
In case you forget your sim pin there is a backup key that is provided to you. It is referred to as PUK [personal unblocking key] code.
Evolution of its size
Sim cards were first introduces in 1991. It looked exactly like a credit card. Most of us today have never seen it. Eventually, just like with other technology, its size shrinks down to mini, micro, and then nano sim . Below is the image to see different sim card sizes.
If you have noticed, there is a cut at one of the corners of the corner. The reason for choosing such a design is to make sure that there is only one way a sim card can be inserted. That cut will help with aligning the contact points correctly on the device.
The most recent development in the industry of sim cards is the introduction to esim. First launched in 2016 over a period more and more devices have launched to be compatible with it. Let’s have a closer look.
E-sim is essentially a digital sim card. There is no physical existence in it. It is embedded into the motherboard of your phone. But with the difference that it is programmable. We have a dedicated article on E-sim which you can read here.
To conclude, sim cards practically act as the brain of your device in terms of providing communication service. With the recent development in e-sim, we can expect a world without physical sim shortly. Before ending this blog, here is an interesting fact. There are more active sim cards on Earth than the entire human population.