# iSIM

> A SIM built directly into a device's main processor rather than a separate chip; the next step in SIM miniaturisation after the eSIM.

Source: https://viasimo.com/glossary/isim/
Also known as: integrated SIM, iUICC

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An iSIM (integrated SIM) is a SIM built directly into a device's main processor rather than existing as a separate chip. It performs the same job as an [eSIM](/glossary/esim/): storing the operator profiles that let a device connect to mobile networks, only with no dedicated SIM hardware at all.

The distinction is physical. A removable SIM is a plastic card, an eSIM is a small chip soldered onto the circuit board, and an iSIM is a secure area built into the system-on-chip that already runs the device. Removing the separate chip saves space, cost and power, which is why iSIM first appeared in smartwatches, trackers and other small connected devices before reaching phones.

| Format | Where it lives | User action |
| --- | --- | --- |
| Physical SIM | Removable card in a tray | Insert and swap by hand |
| eSIM | Dedicated chip on the board | Download a profile |
| iSIM | Inside the main processor | Download a profile |

For travellers the experience is identical to eSIM. An iSIM device downloads the same [eSIM profiles](/glossary/esim-profile/), usually via QR code, and connects to the same networks; the GSMA standards behind both are shared. If your phone has an iSIM, any plan sold as an eSIM should work on it, and the steps in our [eSIM setup guide](/magazine/how-to-install-and-activate-an-esim/) apply unchanged.

The common confusion is thinking iSIM is a different kind of plan or a competing standard. It is not; it is simply the next stage of SIM miniaturisation, following the path described in our [complete guide to eSIMs](/magazine/what-is-an-esim-complete-guide/). Manufacturers like it because it frees internal space and reduces parts; networks treat an iSIM device exactly like an eSIM device.

A concrete example: a cellular smartwatch with an iSIM can carry its own travel data plan despite having no SIM tray and no soldered SIM chip, leaving room inside for a larger battery. If you are unsure what your hardware supports, check [device compatibility](/device-compatibility/) before buying a plan.