It will boot off A drive which is on the right. Unless someone who thinks they know what they are doing has tried to install non-factory drives in it, then it will probably light all drive lights, make some motor noises and do nothing. Somebody who actually know what they are doing will know the floppy interface conforms to Shugart spec, not IBMs bastardised version of it and will configure the drives correctly.

Edit: I don't know if I have to specify that it is low density and will only boot a 360/320k 5.25 disk or a 720k DSDD if correctly converted to 3.5