The latest version of Garmin Express provides the ability to install a map update directly to an SD card.
The SD card installation option will only appear when updating a compatible device that does not have sufficient internal memory for the largest allowable map region. When using the SD card installation option, critical files are loaded to the SD card so it must remain in the device after the update to ensure full functionality. For the largest size SD card a device can use, refer to: What is the largest size Secure Digital (SD) card that an automotive device can accept?
The SD card support during the map update will only function with up-to-date software. It may be necessary to update the device's software with Garmin Express prior to updating the maps.
These devices do not support the SD card option:
For devices that do not support using the SD card with the map update application, any maps that do not fit in the internal memory can be installed to the SD card manually, using these instructions: