Hello John, Leo,

Within a 6500 system with redundant 6500 CatOS the images need to be the same. But this is not required when inserting a new module with different CatOS because at bootup the new backup supervisor image will be synchronized to the active.

On the standby the new image like "BTSYNC_cat6000…" should be automatically downloaded.

Pay also attention to the RAM/FLASH memory requirments of the image in the new card. If there is no free space a question may be asked to erase the old image.

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http://www.cisco.com/en/US/products/hw/switches/ps708/products_configuration_example09186a0080a98f3c.shtml#hm

By default on the Cisco Catalyst 6500 Series  Switch, the Catalyst OS software images on the active and the standby  Supervisor Engines must be the same. If the two supervisor images are  not the same version during system bootup, the active Supervisor Engine  downloads its current boot image to the standby Supervisor Engine. The  NVRAM configuration of the active Supervisor Engine is also synchronized  between the Supervisor Engines.

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Of course the goal is to reach the high availailability operational mode between the two cards => show system highavailabilty need to be enabled and operational.

There is some specificities regarding versioning feature which allows to run different images with still highavailability but I would not pay attention to this feature : 

http://www.cisco.com/en/US/docs/switches/lan/catalyst6500/catos/8.x/configuration/guide/redund.html#wp1046825

Check also for this complete document => http://www.cisco.com/warp/public/cc/pd/si/casi/ca6000/tech/hafc6_wp.pdf

discussing on the global redundancy on the SUP, but also on the MSFC !

Regards.

Karim