Apple - Always boot windows, unless option is held down

From: Boot Camp: Set the default operating system

After installing Windows, you can set the default operating system.

Set the default operating system in OS X

1. In OS X, choose Apple menu > System Preferences, then click Startup Disk.
2. Select the startup disk with the default operating system you want to use.
3. If you want to start up using the default operating system now, click Restart.

Set the default operating system in Windows

You can’t change your startup volume to an external FireWire or USB drive while you're using Windows.

1. In Windows 7, click the Boot Camp icon in the system tray, then choose Boot Camp Control Panel. In Windows 8, move the cursor to the upper-right or lower-right corner of the screen, then click Search. Search for “Boot Camp,” click Settings, then click Boot Camp.

2. If a User Account Control dialog appears, click Yes.

3. Select the startup disk with the default operating system you want to use.
4. If you want to start up using the default operating system now, click Restart. Otherwise, click OK.

Restart in OS X using the Boot Camp icon in the system tray

In Windows, click the Boot Camp icon in the system tray, then choose Restart in OS X. This also sets the default operating system to OS X.

If you don’t see the Boot Camp icon in the system tray, click the triangle to show hidden icons.