What is SIM (Subscriber Identity Module)? - Explained

What is SIM (Subscriber Identity Module)? - Explained

What is SIM?

SIM or Subscriber Identity Module or Subscriber Identification Module is a commonly named as a card which needed to operate the smart phone, mobile device. Inside the SIM there is an IC or an integrated circuit that embedded with the International Mobile Subscriber Identity which also known as IMSI number and the key which needs to authenticate cellular network providers.

Apart from the Smart Phones and other devices, in 4G routers and satellite phones, Satellite Internet Adapters or dongles, uses the same SIM card to validate the users and the number from the cellular network provider.


SIM is made out of PVC and the inside there are semiconductors which does the electronic part of the SIM card. SIMs can be used in multiple devices if the handset is supported for SIM version but only one at a time.

SIM contains it's unique serial number which is known as ICCID, international mobile subscriber identity (IMSI) number, security authentication and ciphering information, temporary information related to the cellular network and two passwords which are personal identification number also known as PIN number and personal unblocking code also known as PUC. 

Inside the SIM card there is a small 64 KB and 128KB memory capacity which is capable to store data inside the SIM card. This space is mostly used to store the contact details of the phone book in the early days.

SIM Versions

1991Full SIM1FF
1996Mini SIM2FF
2003Micro SIM3FF