A SIM card or Subscriber Identity Module is a portable memory chip used in mobile phones. The SIM card makes it easy to switch to a new phone by simply sliding the SIM out of the old phone into the new one. A SIM card contains its unique serial number, internationally unique number of the mobile user or the service-subscriber key (IMSI), security authentication and ciphering information, temporary information related to the local network, a list of the services the user has access to and two passwords (PIN for usual use and PUK for unlocking). In simple terms, it holds personal identity information, cell phone number, phone book, text messages and other data. It can be regarded as a mini hard disk that automatically activates the phone into which it is inserted.
SIM cards are generally used with carriers that operate on the Global System for Mobile Communication (GSM) network. The competing network is Code Division Multiple Access (CDMA), a technology created by U.S. Company, Qualcomm. The first SIM card was created in 1991, with Munich-based smart card maker Giesecke & Devrient selling the first 300 SIM cards to Finnish wireless network operator Radiolinja.
SIM cards are available in three standard sizes. The first and the oldest are in the size of a credit card also known as full-size card (85.60 mm 53.98 mm x 0.76 mm). The development of physically smaller mobile devices prompted the development of a smaller SIM card, the mini-SIM card. It has the same thickness as the full-size cards, but a length of 25 mm and a width of 15 mm, and has one of its corners truncated (chamfered) to prevent misinsertion. The mini-SIM card has the same contact arrangement as the full-size SIM card and they are normally supplied within a full-size card carrier, attached by a number of linking pieces. This arrangement (defined in ISO/IEC 7810 as ID-1/000) allows for such a card to be used in a device requiring a full-size card, or to be used in a device requiring a mini-SIM card after cleanly breaking the scorings manufactured in the outline of a mini-SIM card.
The newest SIM card is known as the 3FF or micro-SIM, which has dimensions of 15 mm 12 mm. Most cards of the two smaller sizes are supplied as a full-sized card with the smaller card held in place by a few plastic links; it can easily be broken off to be used in a device that uses the smaller SIM. The specifications for the 3FF card or micro-SIM also include additional functionality beyond the physical card size.