SIM (Subscriber Identity Module) card is an integrated circuit chip that is used in mobile phones. It stores the required information regarding the international mobile subscriber identity (IMSI) number and its related key which are used to identify and authenticate subscriber’s mobile phones.
The SIM cards come in four standard sizes:
- Full-size (85.6mm × 53.98mm × 0.76 mm)
- Mini-SIM (25mm x 15mm x 0.76mm)
- Micro-SIM (15mm x 12mm x 0.76mm)
- Nano-SIM (12.3mm × 8.8mm × 0.67mm)
The first one was the full-size or 1FF (1st Form Factor) which is similar to the size of a credit card (85.60 mm × 53.98 mm × 0.76 mm). Second one is a mini-SIM or 2FF (2nd Form Factor) which has the same thickness but is 25 mm long by 15 mm wide with one of its corners cut to prevent misinsertion. Third one is a micro-SIM or 3FF (3rd Form Factor) with dimensions of 15 mm × 12 mm and the last one is a nano-SIM or 4FF (4th Form Factor) with dimension 12.3mm × 8.8mm × 0.67mm which was introduced in 2012.
SIM cards also stores SMS messages and phone book contacts. Modern SIM cards can usually store over 250 name/number pairs and up to 50 SMS text messages.
SIM also stores network state information which is received from the Location Area Identity (LAI). But SIM card cannot store multiple numbers per contact or other more complex information.