Stands for "Subscriber Identification Module Card." A SIM card is a small removable chip that identifies a mobile device on a cellular network. It contains an integrated circuit that stores a unique identifier called an "international mobile subscriber identity" (IMSI) number and other information specific to the mobile carrier.
A SIM card or an embedded SIM is required in order for any cell phone, smartphone, or tablet to be used on a cellular network. When you activate a cell phone, the cellular provider links your phone number to your SIM card, which allows you to make receive calls and access cellular data. If you replace your SIM card or a get a new phone with a new SIM card, the new SIM identifier must be linked to your account in order for your mobile device to be recognized on the network.
SIM cards have been standardized in increasingly smaller sizes since the first SIM card was used in 1991. Below are several SIM card formats.
- Full size (1991) - 85.6 x 53.98 mm x 0.76 mm
- Mini-SIM (1996) - 25 x 15 mm x 0.76 mm
- Micro-SIM (2003) - 15 x 12 mm x 0.76 mm
- Nano-SIM (2012) - 12.3 x 8.8 mm x 0.67 mm
Cellular devices are designed to work with a specific SIM card format so if you need to replace your SIM card, it is important to verify the correct size with your cellular provider.
Removing a SIM card is usually pretty simple. Some devices, like the iPhone, have a SIM card tray that pops out from the side of the device. You can open the tray by pressing the access hole with a paperclip. Other devices, such as the Samsung Galaxy, require you to remove the back cover and battery to access the SIM card. You can remove and replace the SIM card without powering down your device.