An Operating System does 'not' install on a 'Motherboard'! Your MB does have a Bios installed.
When you run the install disc it offers you to 'select' an HDD/SDD on your PC, You choose it. So that means it must have used the 'default' or 'only' HDD it ...
When you run the install disc it offers you to 'select' an HDD/SDD on your PC, You choose it. So that means it must have used the 'default' or 'only' HDD it ...