Once upon a time, a call from a mobile phone required a connection to the database when determining the number of the caller. The phone could have a standard set of numbers, and the flexibility of choice simply did not exist. In order to ease the agony of telephone communication customers, individual plates with microchips were invented, which are still in use today.
The SIM card is assigned a serial number, part of which is used by customers for calls. This number refers to the "profile" of the individual number, which is in the operator’s database, and contains all the information about the amount of money in the account, services, etc.
The new invention has protection in the form of a PIN password, which prevents access to the identifier’s public network. If the password has been entered several times in a row, then the system requests additional passwords PUK, PUK2 and PIN2, which are included with the SIM card. Currently, the phone’s settings have the option to disable the password request, so this protection is rarely used.
In addition to these codes, the device has one more that is not communicated to the user - this code is used only by the system when sending a response to the database. Without it, a person will not be able to recreate the chip or copy it.
Architecturally, a SIM card is a primitive computer with all the standard attributes, such as a processor, the amount of internal and RAM. Despite the rather large size of the full version (approximately like two thumbnails), only a small part of what is presented to people is used. Modern phones use smaller versions of SIM cards (micro-SIM and nano-SIM) to save space inside the device. The first SIM cards reached the size of bank electronic keys, which, of course, was inconvenient.
Sim Card Composition
The SIM card is technically a computer whose architecture consists of eight contacts (six in nanoSIM). It includes:
- Own processor with a clock frequency of 10 MHz (no longer needed), it is powered by the phone’s battery.
- RAM - takes up 20% of the total volume provided by microcrystals. It is used to perform operations with numbers and support the user interface (but most of this work rests with the software of the phone itself).
- Internal memory - the rest of the memory used to save numbers, messages, call history, etc. Do not confuse it with the memory intended for phone files - the SIM has nothing to do with it.
- The random number generator is a hardware add-on that is used in the background operation of the system.
- Encryption module - used to recognize passwords and, possibly, generate new ones.
Interesting Facts
The first SIM cards were large, as they were used in pay phones and other places where it was necessary to manipulate pieces of plastic, holding them in hand. The vast majority of the surface was occupied by plastic, which was removed as the cards were reduced (miniSIM and microSIM). The technical part remained exactly the same. In nanoSIM, the microcircuit is shortened by one quarter, but this does not affect the functionality in any way.
Some mobile devices of the latest models use a built-in SIM card, which represents additional contacts in the phone's board. This approach removes from the manufacturer the need to equip the SIM input, but it robs the user of the ability to change the number.
It is noteworthy, with the rapid development of technology over several decades, the "filling" of SIM-cards has not changed. Most telephony users still use the same chips that were invented in the last century.
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