strange problem arose

[babbojoe]

i have an iMac with two external HDs. on one of the HDs i upgraded from mavericks 10.9.5 to yosemite. everything worked fine.

then i needed to scan something with a scanner that is not supported beyond 10.6.8, so i went to the startup discs and selected the 10.6.8 system on the internal HD.

after the scan i wanted to go back to yosemite, but it no longer shows up as a startup disc. disc utility says the yosemite partition is fine.

appreciate any ideas.

 

[Jesla]

Set the boot to which ever partition/disk you want in Setting>Startup disk

 

[babbojoe]

hope i'm putting this in the right place.

my problem is that the yosemite disc no longer showed up in the startup list.

but apparently the answer was 'hold down the option key' on restart. i've been out of school too long.