It is Subscriber Identity Module which is a changeable smart card for
mobile phones. Subscriber Identity Module cards store the information to
identify the user of mobile. It also contains required data for speech
encryption to make trapping other’s calls almost impossible.
Therefore the customer ID and personal
number is tied to the SIM card and not to the mobile phone. This allows a
smooth interchange of SIM card between different GSM mobile phones.
It also used to store SMS and contacts.
Currently SIM cards can store up to 250 name-number pairs and around 50 SMS. There
are certain types of phones (CDMA, TDMA, AMPS) that do not use a SIM card. In
those required data is programmed directly into the phone.
The SIM cards comes mainly in four
sizes:
·
Full-size (85.6 × 53.98 × 0.76)
·
Mini-SIM (25 x 15 x 0.76)
·
Micro-SIM (15 x 12 x 0.76)
·
Nano-SIM (12.3 × 8.8 × 0.67)
The first to appear was the full-size
or 1FF (1st Form Factor), the size of a credit card. It was followed by a
mini-SIM or 2FF (2nd Form Factor), which has the same thickness, with one of
its corners cut to prevent wrong attachment. Next came micro-SIM or 3FF (3rd
Form Factor).
In 2012 the nano-SIM or 4FF (4th Form
Factor) was introduced. Nano-SIM cards can use adapters to gain compatibility
with devices having Micro-SIM and Mini-SIM slots. A Micro-SIM can also be
fitted in Mini-SIM slot with an adapter.
There is a numeric password related
with a SIM card i.e. PIN (Personal Identification Number). User needs to input each
time they start the device. It can be turned off via phone settings. There are
only three chances given to input the PIN. If all three are incorrect, the card
gets locked and a PUK (Personal Unblocking Key) must be entered in order for
the card to work again. Only ten attempts for entering the PUK are allowed
before the card is forever locked and made unworkable.