Install disk restart holding 'C' or 'Option' ?

[daggett2]

DU tells me 'the volume macintoshHD needs to be repaired'
error: the underlying task reported failure on exit
volume needs repair

so i need to startup from my install disc
ok i've had to do that before

but some resources say to restart while holding down the 'C' key, others the 'Option' key.

i think i've done it before using the 'option' key. not sure now.

my question:
-what's the definitive one to use for this?
-and what's the difference? (i've read what they do differently but don't really understand the difference)

Also:
my AppleCare just ran out and i understand it can't be renewed. is there another option available? or is apple's 'pay per incident' the only way from now on?

thank you all!
this is an invaluable forum

 

[Eidorian]

'C' boot from optical drive.

"Option" show the boot loader which includes the optical drive.

 

[daggett2]

so it doesn't really matter then
the 'option' just adds another step in this instance
thank you

 

[Neil321]

so it doesn't really matter then
the 'option' just adds another step in this instance
thank you

You need to boot while holding down the c key ( insert disk ), the option (alt key) like Eidorian stated brings up the bootloader ( ie if you have two OS's installed say OS X & XP )