Wondering what is saved in a SIM card? The question is in no way surprising to us. After all, most of us carry this tiny golden chip enveloped in PVC inside our devices. But, we never truly look at its capabilities. So, what is saved there? The short answer is not much and quite a lot, depending on how you look at it. But, we here at HybridSIM value precision, and it’s time we provide it to you. Let’s get into what is stored inside a SIM card.
Q: What is the storage space in a SIM card?
A: Depending on the generation (also called “form factors” or SIM card sizes), the SIM card can carry between 8 KB and 256 KB of data. The thing is – most of this storage space is already taken by the carrier, and inaccessible to users.
Things stored in a SIM card
1. Your identity and location on the network
It’s in the name – Subscriber Identity (or Identification) Module. Each SIM card also stores a unique Personal Identification Number (PIN) or Personal Unblocking Key (PUK) that is printed on the full-size SIM card. Additionally, each card has a unique ICCID (Integrated Circuit Card Identifier) printed near the golden chip. These are key to the functionality, and without them, your SIM card would not be working.
The PIN/PUK number works in unison with IMSI (International Mobile Subscriber Identity). This combination is what allows you to make and receive calls and send text and multimedia messages inside or outside your native network. If you leave the area covered by the carrier, your location is still tracked, and you enter the so-called roaming. The data on the SIM card, including your location, is used to log activities and calculate fees and allows the carrier to send you a precise, but a hefty bill.
2. Authentication Key (Ki)
This 128-bit key works in the same way as IMSI, only for GSM networks. To clarify, it allows you to access mobile data (Internet) inside or outside of your carrier’s network.
There is no precise way to determine the number of contacts that can be saved on a single SIM card. It depends on the type of the card, its free storage space, the length of contact names, whether a picture is added, how many numbers (or e-mails) are saved under one entry, etc. In any case, it is always best to make a cloud backup for this type of information.
4. Text messages
Text messages (SMS) can be saved on a SIM card, but are most often saved inside your device’s internal memory. You can manually save some of them on a SIM card, of course. However, we would stick to the extremely important ones, and keep their number low.
5. SIM Toolkit
A SIM toolkit has two main purposes. The first allows you to check the status of your monthly bill (for postpaid SIM cards) or remaining calls, SMS, or mobile data for prepaid SIM cards. The second one is the carriers’ way of extracting more money out of its users by offering promotions, additional services, subscription plan upgrades, paid downloads, etc.