Subscriber Identity Module (SIM)

SIM card as the name suggests is integrated circuit that stores identity of users on mobile telephony devices. SIM card is generally smaller and rectangular, about 25mm by 15mm, and notched at one corner.

This feature ensures handy, fail-safe way of inserting the card correctly into the slot in mobile phone. SIM cards can also be used in satellite phones, smart watches etc. SIM cards can be transferred between different phones. SIM cards consist of unique serial number, international mobile subscribe identity (IMSI) number, ciphering information, information related to local network. SIM cards are used in GSM mobile phones while CDMA phones uses Reusable Identity Module (RUIM).

It also has limited memory which can be used for storing contacts of person using that SIM card. For example when we save new contact in mobile phone, we are given to options that whether we want to save it in sim card or in phone storage and when we select the option of sim card the contact gets saved in SIM card.
This proves that SIM card is portable smart card which is movable among different phones.

SIM Memory Structure :
The SIM memory structure is said to be consist of directories which are analogous to the directories of traditional hard disk drive.The file system consist of Master File(MF), directory file(DF) and elementary file(EF).

  1. Master File –
    Master file is root of file system.It is analogous to root directory like in any of operating systems.It may or may not elementary files(EF). It may contain one or many dedicated files(DF).

  2. Dedicated File –
    It is sub directory. It can be identified by two byte identifier. The phonebook EF falls under this category.
  3. Elementary File –
    These files lie below dedicated files in memory hierarchy system.These files contain actual data. It would not be wrong to say that EF represents leaf node of the system.

Advantages of Subscriber Identity Module :

  • This tiny card consist of your phone number, rate plan, your contact list and several other things.
  • It is portable chip which you can move from one cell phone to other.
  • The data on SIM card is protected by PIN lock which is usually set by manufacturer. Although you can change this PIN.

Disadvantages of Subscriber Identity Module :

  • As the SIM card is portable so if anytime you loose it you loose your personal information like phone number, contact list and several others.
  • If you are using dual SIM handset it is possible that phone battery may drain lot.
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