Getting Started

SIM Card Types Explained

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Complete guide to SIM card types and form factors: Mini, Micro, Nano, eSIM (eUICC), iSIM, and SoftSIM with use cases and evolution.

  
  

    
    
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    4 min read
    
  








  
  

    
    
      
      
  1. 
        SIM Card Types Explained
      
    2. 
      
      
  2. 
        Form Factor Timeline
      
    3. 
      
      
  3. 
        Electrical Interface: What Never Changed
      
    4. 
      
      
  4. 
        eSIM: From Removable to Embedded
      
    5. 
      
      
  5. 
        iSIM: The Integrated Approach
      
    6. 
      
      
  6. 
        Choosing the Right Form Factor
      
    7. 
      
      
  7. 
        SIM Operating System and Security
      
    8. 
      
    

  









  
  

  
  

    
    

      
SIM Card Types Explained


The Subscriber Identity Module (SIM) is one of the world's most
deployed smart card variants. Since its introduction in 1991 it has shrunk from a
full ID-1 credit-card form factor to a sub-millimetre solder-mounted chip. This guide
traces the physical and technical evolution across all major form factors.


Form Factor Timeline






Form Factor
Formal Name
Dimensions
Introduced
Thickness






Full-size (1FF)
ID-1
85.6 × 54.0 mm
1991
0.76 mm




Mini-SIM (2FF)
ID-000 plug-in
25.0 × 15.0 mm
1996
0.76 mm




Micro-SIM (3FF)
—
15.0 × 12.0 mm
2003/2010*
0.76 mm




Nano-SIM (4FF)
—
12.3 × 8.8 mm
2012
0.67 mm




eSIM (MFF2)
Embedded
6.0 × 5.0 mm
2016
0.8 mm




iSIM
Integrated
Die-level
2018
N/A






*Micro-SIM was standardised in 2003 but popularised by the iPad in 2010.


Each shrink removes the plastic carrier while keeping the same contact pad
layout defined in ISO 7816 — the electrical interface is
identical across 1FF through 4FF.


Electrical Interface: What Never Changed


All removable SIM form factors share the ISO 7816-2 contact layout:






Contact
Name
Function






C1
VCC
Supply voltage (1.8 V / 3 V / 5 V)




C2
RST
Reset signal




C3
CLK
Clock input




C5
GND
Ground




C7
I/O
Bidirectional data (T=0 protocol)




C4, C6, C8
RFU / USB
Reserved or USB differential pair






SIMs exclusively use T=0 — the byte-oriented half-duplex protocol —
unlike general-purpose smart cards which may also negotiate T=1.
The ATR transmitted at power-on identifies voltage class and
supported features; parse it with the ATR Parser.


eSIM: From Removable to Embedded


The embedded SIM (eSIM) is soldered directly to the device PCB and ships pre-loaded
with a bootstrap operating system. Its operator credentials are provisioned
over-the-air via GSMA Remote SIM Provisioning (RSP) — see the
eSIM Remote Provisioning Guide.


Key eSIM properties:
- MFF2 package: a rugged surface-mount component rated for –40 °C to +105 °C,
  suitable for automotive and industrial deployments
- GSMA SGP.22: consumer RSP — users switch profiles via device UI
- GSMA SGP.02: M2M RSP — profiles pushed by operator without user interaction
- Multiple profiles: up to the chip's EEPROM capacity (typically 3–8 profiles)


iSIM: The Integrated Approach


The iSIM (integrated SIM) takes miniaturisation further by embedding
the SIM function as a dedicated security partition inside the application SoC — the
same chip that runs the CPU, modem, and GPU. Qualcomm's X60 modem and ARM's Corstone
platform both incorporate iSIM logic.






Dimension
eSIM (MFF2)
iSIM






Die location
Separate chip
SoC partition




Board area
~30 mm²
Negligible




Certifiable boundary
Own die
TrustZone / TrustZone-M




Replacement
Requires rework
Not replaceable




Common Criteria EAL
EAL4+ typical
EAL4+ (SoC-level)






Choosing the Right Form Factor


    

  • Consumer smartphones: Nano-SIM slot + eSIM dual-capability is now standard
    • 

  • Wearables and earbuds: eSIM MFF2 (no slot space)
    • 

  • Industrial IoT: eSIM MFF2 for ruggedness; iSIM for bill-of-materials reduction
    • 

  • Automotive: eSIM MFF2 (AEC-Q100 qualified variants)
    • 

  • Legacy infrastructure: Mini-SIM still used in some M2M modems
    • 



Use the eSIM Checker to verify whether a specific device
model supports consumer or M2M RSP before designing a provisioning workflow.


SIM Operating System and Security


Whether removable or embedded, all SIMs run a proprietary OS certified to
Common Criteria — typically EAL4+ against the GSMA SAS
protection profile. The security boundary enforces:


    

  • Authentication key (Ki) never exported in plaintext
    • 

  • PIN/PUK retry counters with lockout
    • 

  • Applet isolation (via JavaCard in modern USIMs)
    • 

  • OTA update authentication via SCP80
    • 



The next level of detail — remote provisioning architecture — is covered in the
eSIM Remote Provisioning Guide.

    

    

    
    
    
    

    
    

      




  
Frequently Asked Questions


  

    
    

      
      

        
Our guides cover a range of experience levels. Getting Started guides introduce smart card fundamentals. Security guides address Common Criteria certification and key management. Programming guides target developers working with APDU commands, JavaCard applets, and GlobalPlatform card management.