A SIM is a full blown computer

[Lucian]

Ok, this is both surprising and eye-opening, I always thought a SIM is just read-only memory.

What is AT&T doing at 1111340002? | Hacker News

news.ycombinator.com

"A SIM card is a full blown computer with its own CPU and memory.
Your carrier can upload and run arbitrary code without your consent or knowledge. They can do this at any time.
This means that your "phone" is actually three different computers running in concert - the actual phone itself (iOS or Android or Symbian), the baseband processor running the baseband code, and the SIM card."

Example hardware from the same link:
"Atmel AT90SC25672RU, 8-bit AVR, 256KB ROM, 72 KB EEPROM, 6 KB RAM, Between 20 & 30 MHz"

 

[Bubblesthefish6]

Ok, this is both surprising and eye-opening, I always thought a SIM is just read-only memory.

I didn't realise the extent of what they can do through a SIM but I did know that they weren't read only as you used to be able to store contacts on them back in the days of Nokia - I am to believe you can still write contacts to a sim now.

 

[The Wee Bear]

Yes you can still import and export your contacts to your sim Bubbles.
I find it easier just to store them in the cloud.

Won't be too happy if someone deletes the cloud one day though.

 

[Bubblesthefish6]

Yes you can still import and export your contacts to your sim Bubbles.
I find it easier just to store them in the cloud.

Won't be too happy if someone deletes the cloud one day though.

I have them stored in two Google accounts, my mi account and as a backup, my SIM!!!!

 

[The Wee Bear]

I have them stored in two Google accounts, my mi account and as a backup, my SIM!!!!

I think that's you well covered then Bubbles.

 

[Meatball]

This is now a bit dated but provides a good background to how we got to UICC cards.

http://miun.diva-portal.org/smash/get/diva2:423013/FULLTEXT02.pdf

LTE Advanced and 5G of course are layered on top of this now and we are moving to eSIM to overcome the limitations of the physical SIM.

Shows why we should always respect the smallest of electronic devices.