What is a SIM card?
The first generation mobile phones were identified by the network using embedded equipment. This meant, in particular, that when the device was changed, the subscriber automatically changed his phone number. An alternative was to contact a specialized salon owned by a telecoms operator, in which they changed the firmware of the device for money in order to keep the old number.
This approach deprived cell phones of a certain proportion of mobility. To eradicate these inconveniences, the concept of a SIM card was developed. This abbreviation stands for Subscriber Identification Module or subscriber identification module. To understand what a first-generation SIM card is, imagine a credit card - this is exactly the size of the first SIM cards. Even with this size for its time, this technology was a breakthrough, allowing subscribers to change telephone sets without unnecessary worries. In addition, the size of the first mobiles and did not require a smaller card format.
SIM card device
For most users, a SIM card looks like a piece of plastic on which small metal pads are applied. However, the internal structure of a sim card is not as simple as its appearance.In fact, this is a small computer. It contains a microprocessor that provides data exchange between the telephone and the card itself, an internal memory chip and a permanent memory in which various information is recorded. For the operation of the SIM card, special software is used, which is integrated into it.
The card itself is identified by the cellular network using its IMSI (unique subscriber number). Telephone number of the subscriber (which is denoted by the abbreviation MSISDN) is assigned to the map when it is registered in the network. Therefore, if you lose / replace the SIM card, it is quite easy to restore the number. To do this, a record of the correspondence of the old telephone number to the number (IMSI) of the new SIM card is made in the equipment of the operator.
Dimensions of modern SIM cards
The fact that such a SIM card is now known to any owner of a modern mobile phone. The format of a conventional SIM card is still the most popular. The size of such cards is 25x15 mm. Thickness - 0.76 mm. At the same time, the size of the electronic device placed in it is much smaller. The area occupied by metal pads on the surface of the card is much less than 50% of the surface.
Companies that produce smartphones (Samsung and others), apparently decided that a few extra milligrams of plastic, which the owners of the SIM have to carry, are too heavy and unjustified burden. Thus was born the new standard - micro SIM. You can understand what a Micro-SIM card is, if you imagine a piece of plastic measuring 15x12x0.76 mm. This standard was used in the iPhone 4, iPad Galaxy III and several other devices.
But progress does not stand still, and, trying to keep up with it, mobile device manufacturers decided to make their SIMs even smaller. Everyone who managed to get an iPhone 5 learned about what a Nano is a SIM card. Many were unpleasantly surprised by the discovery. Nano-SIM is a card with dimensions of 12.3x8.8x0.67 mm. This surprise turned out to be unpleasant because the new devices were unable to accept large SIM cards, and some subscribers could not acquire a new map (nano-sized) due to their shortage (the problem, in particular, affected the citizens of Russia and Ukraine).
Previously, when switching from mini-SIM to micro-Sim, the problem was solved with scissors (since the difference was only in the amount of plastic, while the interface and geometry of the contact plate were the same): the mini SIM card was cut to the size of a micro-SIM.In addition, some cards were issued in the case of a full-sized card (about the size of a credit card), from which one could easily “break out” a SIM card in a mini or micro format. The nano-SIM standard is very different from its predecessors and does not allow such "transfers".