Full form of SIM

The Subscriber Identification Module, or SIM, is the complete form of the term. The SIM, or international mobile subscriber identity, is a built-in circuit and portable chip that securely contains the IMSI. We can make phone calls to anyone in the world with an intelligent memory card as long as the user's contact network remains consistent.
GSM networks that are managed and operated by smartphones typically employ SIM cards. Any user with an electronic device capable of supporting this can utilize it because it is movable.

Past Events

Munich-based smart card manufacturer Giesecke and Devrient produced the first SIM card in 1991. The European Telecommunication Standards Institute was the organization that first acknowledged and announced the SIM.

The SIM card's function

In addition to storing a large amount of data, a SIM card also transmits and receives vital information amongst its network of users and retains some of their private and personal information. The list of data that SIM stores is

• Details of the address
• SMS texts
• Keys to personal security
• Telephone number
• Information about network permission.
• Other data.

The following is a list of some important data that SIM carries.

• Information about security
• IMSI (International Mobile Subscriber Identity)
• unique serial number
• A summary of the local network.

Dimensions of the SIM

When SIMs were initially manufactured, they were around the size of credit cards; however, later disclosures of the SIM's dimensions revealed that its capacity was 15 mm by 12 mm. Different nano- and micro-SIM chip sizes are currently used in some devices.

Contents of a SIM.

It has an IMSI number, or International Mobile and Subscriber Identity, a unique number that serves as a serial for it, features for identification and authentication, network data that is momentarily saved, and ciphering information. A SIM is secured with a PUC (personal unblocking code) to enable PIN unlocking, and it also contains a record of the services that customers have used. PIN and PUK unblocking keys are four to eight-digit passwords that are used to protect the SIM from unauthorized use. But it's not always necessary to use a PIN.

By simply moving the SIM card to the phone he is using, a user can use any SIM card that they own. These cards are also used in satellite devices, smartwatches, and other gadgets.

SIM structure and memory hierarchy

The Subscriber Identity Module's memory structure is similar to that of a device's directory.
The file system used by SIM consists of three files: a directory file (DF), an elementary file (EF), and a master file (MF).

Master file:

The master file (MF), or what you can call its roots, is the foundation of the file system. The fundamental directory seen in any other OS (operating system) is fairly similar to the master file. It's not required that this file be an EF (elementary file). In the SIM file system, there may be one or more dedicated files.

Dedicated file:

Dedicated files, sometimes known as dedicated files DF, are the MF's subdirectory or subordinate folders. The GSM11.11 standards define the features and the consistent data of specialized files.
A two-byte identifier is used to identify the specialized files. The same class includes the phonebook elementary files as well.

Elementary file:

Under the SIM memory hierarchy settings, elementary files are located underneath dedicated files. Consider the fundamental files to be the file system's leaf node.

It is crucial to remember that only the elementary files store data; all other files in the file system have headers. The first byte of the header, which also includes information on the file system's structure, identifies the type of file.

Within the body of the elementary files is contained application-related data.
The file structure may be categorized as administration- or application-specific. The operating system decides who can access the stored data.

Advantages of SIM

The advantages of a subscriber identity module card are as follows:

• This tiny smart card has many more things in addition to your contact number and the phone numbers of your connections in a phonebook.
• This little card is readily accessible and movable between phones.
• The SIM card contains files that are protected by a PIN lock, which is frequently provided by the provider. But you can access the PIN change.