Why is flash memory erased prior to upgrading the IOS image from the TFTP server?

Question:
Why is flash memory erased prior to upgrading the IOS image from the TFTP server?

• The router cannot verify that the Cisco IOS image currently in flash is valid.
• Flash memory on Cisco routers can contain only a single IOS image.
• Erasing current flash content is requested during the copy dialog.
• In order for the router to use the new image as the default, it must be the only IOS image in flash.

Explanation: During the copy process, the router asked “Erasing flash before copying? [confirm]” and the administrator confirmed (by pressing Enter) so the flash was deleted.

Note: In this case, the flash has enough space to copy a new IOS without deleting the current one. The current IOS is deleted just because the administrator wants to do so. If the flash does not have enough space you will see an error message like this:

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