SIM card
A subscriber identity module or subscriber identification module ( SIM ) An integrated circuit that is intended to securely store the international mobile subscriber identity (IMSI) number and its related key , used to identify and authenticate subscribers on mobile telephony devices . Full-size SIM ( 1FF, 1st form factor) Mini-SIM (2FF) Micro-SIM (3FF) The use of SIM cards is mandatory in GSM devices. CDMA -based devices originally did not use a removable card, and the service for these phones bound to a unique identifier contained in the handset itself. This is most prevalent in operators in the Americas. SIM CARD PINS VCC (Power supply) RST (Reset) CLK (clock) D+ (USB Inter-chip) GND (ground) VPP (voltage programming power) I/O (input/output) D (USB inter-chip)