Hadi,
Hello, so you can't really change the boot device. What is it you are really trying to accomplish?
What you are looking at there are PRPs in 4 and 5 and different linecards in the others, correct? The RPs will boot off disk0. While the linecards will memboot after the PRPs have come up. This is normal.
You can have a PRP do a memboot, but this is not supported for production routers. The down side would be you can't later add packages or SMUs. This is usually only done in a lab environment.
As for different boot devices, you can have disk0: disk1: as devices on the PRPs.
Take a look at the following doc for setting up disk mirroring and backups and such.
http://www.cisco.com/en/US/docs/routers/crs/software/crs_r3.9/system_management/configuration/guide/yc39crs1_chapter3.html
Thanks,
Bryan