Eject a disc so you can insert the disc you want to start from.

Here’s the scenario:

You want to install Snow Leopard on your Mac but, for whatever reason, there’s a bootable CD or DVD in your computer’s optical drive. If you hold down C while starting up, it’ll boot from that disc. If you don’t hold down anything while starting up, it’ll boot from whatever disk it last started from or the disk set in the Startup Disk preferences pane. If you repeatedly press the Eject Media key while starting up, it may or may not eject the disc you don’t want to start from — in any case, it’ll likely start before you can insert the correct disc.

Sound far-fetched? It isn’t. It happened to me the other day.

My iMac’s hard disk was feeling ill and simply wouldn’t boot. I’d last started it with my old Leopard install disc inserted. When I got my Snow Leopard Install disc, I decided to run its Disk Utility First Aid routine on the sickly hard disk. Trouble was, I’d shut down the computer with the Leopard disc inserted.

Here’s how to eject a disc so you can insert another disc for startup. (The “screenshots” here were created with my digital camera, since it’s impossible to create a screenshot from within Mac OS X before the computer has completed its startup process.)

1. Hold down the Option key while starting your Mac. Keep the key held down until a screen with startup disk icons appears.
   
2. Click the icon for the disc you want to eject to select it.
3. Press the Eject Media button on the keyboard. The disk comes out and its icon disappears from the screen.
   
4. Insert the disc you want to start from. Its icon appears onscreen.
   
5. Click the disc icon to select it.
6. Press Return. The computer completes the startup process, using the disc you selected.

As you may already know (or should have realized after reading this), if you hold down the Option key at startup, you can choose your startup disk on the fly. You might find this useful if, for some reason, you have multiple bootable disks on your computer.

It’s in the Book!

You can find more information about hard disks and using Disk Utility with Mac OS X 10.6 Snow Leopard in Mac OS X 10.6 Snow Leopard: Visual QuickStart Guide.:

• Storage Media is covered in Chapter 6, pages 97-126.
• Mac OS Utilities is covered in Chapter 24, pages 569-594.