General software download rules
Switch software that you download via the menu interface always goes to primary flash.
After a software download, you must reboot the switch to implement the new software. Until a reboot occurs, the switch continues to run on the software it was using before the download.
Downloading new switch software does not change the current switch configuration. The switch configuration is contained in separate files that can also be transferred. See Transferring switch configurations.
In most cases, if a power failure or other cause interrupts a flash image download, the switch reboots with the image previously stored in primary flash. In the unlikely event that the primary image is corrupted (which may occur if a download is interrupted by a power failure), the switch goes into boot ROM mode. In this case, use the boot ROM console to download a new image to primary flash.