It's a little confusing to first-time Disk II users who have only used Macs before. If you place a startup floppy in the second drive of a Mac (internal or external), it will boot from the disk even if the first drive is empty.
As coius notes, on an Apple II, only the first drive gets accessed upon boot. The same thing will happen if you're using a DuoDisk drive or the newer UniDisk/Apple 5.25" Drive with the II, II+, or IIe. (There are exceptions with other Apple II models, which I won't get into at the moment).
You'll find few programs actually utilize the second disk drive. Most larger programs either use two-sided disks (called "flippies") or require a second disk to be inserted in drive one--in place of the original.
As coius notes, on an Apple II, only the first drive gets accessed upon boot. The same thing will happen if you're using a DuoDisk drive or the newer UniDisk/Apple 5.25" Drive with the II, II+, or IIe. (There are exceptions with other Apple II models, which I won't get into at the moment).
You'll find few programs actually utilize the second disk drive. Most larger programs either use two-sided disks (called "flippies") or require a second disk to be inserted in drive one--in place of the original.