Subscriber Identity Module

A SIM card, small version

A Subscriber Information Module (a 'SIM') is a smart card securely storing the key identifying a GSM subscriber. The card also contains storage space for SMS's and a phone book.

Early versions consisted of the whole fullsize smart card. Soon the race for a smaller telephones called for a smaller version of the card. The card was cropped down to 25 x 15 mm (As illustrated).

The use and content of the card is protected by several levels of access codes. PIN is the every day access code for normal use of the phone. PIN2 is reqired to use special functions (like limiting outbound telephone calls to a list of numbers). PUK1 and PUK2 is used to reset PIN1 and PIN2 respectivly.

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