We don’t think about SIM cards as much as we used to — like back when they were required to start up a phone — but these tiny chips are still essential in keeping a modern smartphone wirelessly connected at all times. This brings us to a question we should be asking: How exactly does a SIM card work?

Subscriber Identity Module

We all talk about SIM cards without even knowing what it means. As you’d expect, it’s short for Subscriber Identity Module, and it does exactly what it implies: Providing cellular networks with your identity in order to establish a secure connection.

They come in different sizes, with nano-SIMs becoming the new standard because of how small they are, allowing phone manufacturers to leave more space for other vital components in their products. What’s also minuscule is their storage capacity, often limited to 256KB. That, however, is more than enough to store all the important pieces of information, including the identification numbers.

The four universal SIM card sizes

Without getting too technical (and there is a lot to take in when it comes to authentication protocols), every SIM card holds a unique 64-bit number that identifies the device it’s attached to with the cellular network. Being a 64-bit digit, there are more than enough possible combinations for trillions and trillions of subscribers — so, no, you can’t buy all the SIM cards in the world and run out of phone numbers to use.

Connecting to a network

As soon as you turn your phone on with a SIM card inside, it’ll communicate with the network carrier to establish a connection. Once its unique number along with a security authentication key is sent to a nearby tower, the service provider will send encrypted information back in hopes of a match. If your SIM card is able to decrypt the randomized code successfully, your handset will receive its well-deserved wireless signal.

This process ensures only your SIM has the capability of figuring out the encryption and letting you use the mobile number you were provided with — but that’s just for the service itself. What if someone physically gets a hold of your SIM card and decides to use it on his or her phone? That’s where the personal identification number (PIN) and personal unblocking code (PUK) come in.

Phones like the Huawei Mate 9 can accept two SIM cards at the same time

By adding a PIN to your SIM, a four-to-eight digit code will be required to turn it on. If in case someone tries to break in using brute force, the SIM will be locked after three unsuccessful attempts; the PUK, which can be found on the card that comes with every SIM, is needed to release the lock.

The future of SIM cards

What makes SIM cards so popular is how easy they are to transfer from one device to another. Some companies, however, believe we can take this a step further with embedded SIM cards (e-SIM for short). As you can tell by the name, this form would embed itself in a device and can’t be swapped for another. Doesn’t this defeat the purpose of traditional SIMs? Not at all.

By being integrated into the hardware, you can change your network carrier without replacing the physical card. Instead, all you have to do is jump in the phone or tablet’s interface and select from there. Apple already began implementing this technology on its iPads, and Samsung’s Gear smartwatches have been following suit.

While it may sound like a pain in the butt to adjust to yet another new standard, this technology could lead to even slimmer devices and greater convenience once more companies jump on the ship. The hassles of international roaming would also become a thing of the past, since selecting your preferred service would only take a few taps on your screen.

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