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In this issue of **Things In Our Stuff**, we will talk about a small plastic card mostly found in mobile communication devices such as cellphones, tablets, and smart watches. It can also be found in computers, cameras, and even in wireless credit card terminals. It connects about 7 billion devices to cellular networks around the world.

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![TIOS_sim.jpg](https://res.cloudinary.com/hpiynhbhq/image/upload/v1513594237/qhi7wafxdsa0awwlqqrb.jpg)
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I am talking about [SIM](https://en.wikipedia.org/wiki/Subscriber_identity_module) cards. The SIM or the **Subscriber Identity Module** or **Subscriber Identification Module** is an integrated circuit that securely stores the [international mobile subscriber identity (IMSI)](https://en.m.wikipedia.org/wiki/International_mobile_subscriber_identity) number and its authentication key. It also contains some personal information of the subscriber such as the phone number and data plan subscription, temporary information about the network, list of services accessible to users, a personal identification number (PIN), and a personal unblocking code (PUK) for PIN unlocking. It also has a small memory ranging from 32 to 128KB for storing messages and contact numbers. SIM cards are required for [GSM](https://en.wikipedia.org/wiki/GSM) phones but [CDMA](https://en.wikipedia.org/wiki/CDMA) devices only requires it for [LTE](https://en.wikipedia.org/wiki/LTE_(telecommunication)) connectivity. *The equivalent of SIM on CDMA networks is the [R-UIM](https://en.wikipedia.org/wiki/Removable_User_Identity_Module).*

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![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1513595667/lemdyiv5fqyjl8y2r7ef.png)<sub>Image from [Pixabay](https://pixabay.com/en/smartphone-technology-communication-1284501/)</sub></center>

SIM was first developed in 1991 by [Giesecke & Devrient](https://en.wikipedia.org/wiki/Giesecke_%26_Devrient), a smart-card maker from Munich which initially sold 300 sim cards to Finnish wireless network operator [Radiolinja](https://en.wikipedia.org/wiki/Radiolinja). In 2016, about **5.4** billion sim cards are manufactured globally generating over **$6.5** billion revenue for SIM Card vendors.

<center>![Smartcard_chip_structure_and_packaging_EN.svg.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1513594596/gbcllxcjozk2ylqkh5de.png)<sub>The anatomy of a SIM chip by [Justin Ormont, Wikimedia](https://commons.wikimedia.org/w/index.php?curid=9383651)</sub></center>

The first generation SIM cards were the same size of credit cards but technological advancement in chip production and the reduction of size of mobile devices calls for the production of smaller sim cards. Over the years, other form factors of SIM card with different sizes were released. The **full-size (1FF)** SIM cards that were introduced in 1991 is 85.60 mm in length, 53.98mm in width, and 0.76mm in thickness.

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![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1513595259/yjjipejzxujkqxfmr2m4.png)<sub>Different sizes of SIM cards, [Cvdr](https://commons.wikimedia.org/wiki/User_talk:Cvdr), [Wikimedia](https://commons.wikimedia.org/w/index.php?curid=20410641)</sub></center>

It was followed by the **Mini-SIM (2FF)** in 1996 measuring 25mm long x 15mm wide x 0.76mm thick. A much smaller format called **Micro-SIM (3FF)** which is 15mm in length, 12mm in width, and 0.76mm in thickness was released in 2003. The smallest and the latest of all the formats  is the **Nano-SIM (4FF)** introduced in 2012. It has a measurement of 12.30mm x 8.80 mm x 0.67mm only. If you have an iPhone 5 or newer, then your SIM card is a Nano-SIM. Previous version of Samsung Galaxy such as Samsung Galaxy S4 and S5 phones use Micro SIM cards while Galaxy S6, S7 and S8 uses Nano-SIM.

An upcoming form factor is coming known as **eSIM** or *Embedded-SIM* which is a non-replaceable embedded chip soldered directly to a circuit board. eSIM will be 6mm long, 5mm wide and less than 1mm thick.

The SIM card is a vital component of mobile communication that facilitates communication between a device and cellular towers. Aside from IMSI, every sim card is internationally identified by an **Integrated Circuit Card Identifier (ICC-ID)** which is physically engraved on the body of the card. When a sim card is inserted on a mobile phone and the phone is powered up, it will connect to its network through cellular towers. The network will then authenticate the sim card using its **ICC** and **IMSI** and the **authentication key** that validates the IMSI. The phone reads the IMSI from the SIM card and pass it to the network. The network then takes the IMSI and search their database for authentication keys that validates it. 
If a SIM card is validated by the network, then your phone will have access to the network's resources depending on your subscription. You can now make calls, send messages, browse the internet, and use data connection for your apps. All of these depend on your subscription which was stored in your SIM card.

And because your subscriber data is stored in your SIM, you can switch to a new phone by inserting your SIM and continue to enjoy your subscription plan as long as the phone is not locked to a different network.

Most countries and operators require subscribers to register and provide identification before activation of service but some such as the United States, Hong Kong SAR, Lithuania and the Philippines have no mandatory SIM  card registration. 


<center>![image.png](https://res.cloudinary.com/hpiynhbhq/image/upload/v1513676432/pwomptcfjkw2nujylsn3.png)
<sub>screen grabbed from [Sun Cellular](https://suncellular.com.ph/Personal/prepaid/sims-and-rates)</sub></center>

In the Philippines, a prepaid sim card can be bought in the streets for as low as **Php 15 ($.30)** pre-loaded with texts and calls.


<center>
Previous Things In Our Stuff:
[The @ Sign](https://steemit.com/curiosity/@st3llar/things-in-our-stuff-the-sign)
[Transistor](https://steemit.com/curiosity/@st3llar/things-in-our-stuff-transistor)
[Hydrofluorocarbon (HFCs)](https://steemit.com/curiosity/@st3llar/things-in-our-stuff-hydrofluorocarbon-hfcs)
[Triclosan](https://steemit.com/curiousity/@st3llar/things-in-our-stuff-triclosan)
[Modified Starch](https://steemit.com/curiousity/@st3llar/things-in-our-stuff-modified-starch)
[Activated Carbon](https://steemit.com/curiousity/@st3llar/things-in-our-stuff-activated-carbon)

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<center><sub> Sources: [Wikipedia ](https://en.wikipedia.org/wiki/Subscriber_identity_module)• [Lifewire](https://www.lifewire.com/what-are-sim-cards-577532) • [iMore](https://www.imore.com/sim-card) • [TalkAndroid](http://www.talkandroid.com/guides/beginner/how-sim-cards-work/) • [MakeUseOf](http://www.makeuseof.com/tag/why-do-cellphones-need-a-sim-card/) •
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