Note that by default, the Mac will start booting up directly to the external hard drive until you change it. The second method to install OS X is to restart the Mac and press and hold the COMMAND + R keys. This will load up OS X Recovery. The OS X Utilities screen will. Mavericks (OS X 10.9) doesn’t ship on a disc. Instead, it’s available only as an installer app downloadable from the Mac App Store, and that installer doesn’t require a bootable installation disc. This symbol at boot means Mac OS X cannot access critical files on the start-up disk. This symbol at boot means the system has found a bootable installation of Mac OS X on the system, but there is. I tried to clean install OS X El Capitan on my Mac, but it won’t boot from the USB drive. Here are the steps I took to create the bootable USB drive (I have a Mid-2014 MacBook Pro with Retina Display): Downloaded the latest OS X El Capitan (10.11.3) from the Mac App Store.
I have an external USB SSD install with Windows 10.

Jun 25, 2018 Mac Secret Trick - How to Clone Mac Hard Drive with Disk Utility HDD SDD MacBook Pro iMac 2010-2019 - Duration: 10:09. Gunner Tierno x Yeezy God 349,477 views 10:09.
On my MacBook Pro 15' mid 2014 I can press option on boot and it will show up and I can boot to Windows.
However when I try on my MacBook Air 13' early 2015, pressing option on boot doesn't show up the external USB SSD, only macOS partition is shown. When I boot in to macOS, I can view the external USB thus the USB port is not faulty, I also try again on my MacBook Pro and its able to boot up to Windows with no problem
How to access it on my MacBook Air? I tried on both USB ports doesn't work.
The only different is on my MacBook Air I turn on FileVault which is require by my company while the MacBook Pro don't as I use at home.
Any help is appreciated. Thanks in advance.
MacBook Air, Mac OS X (10.7.5)
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Boot Camp Control Panel User Guide
You can set the default operating system to either macOS or Windows. The default operating system is the one you want to use when you turn on or restart your Mac.
Mac Is Booting Software From Drive Instead Of Installing Computer
Set the default operating system
In Windows on your Mac, click in the right side of the taskbar, click the Boot Camp icon , then choose Boot Camp Control Panel.
If a User Account Control dialog appears, click Yes.
Select the startup disk that has the default operating system you want to use.
If you want to start up using the default operating system now, click Restart. Otherwise, click OK.
You can’t change your startup volume to an external FireWire or USB drive while you’re using Windows.
To learn how to change the default operating system using macOS, see Get started with Boot Camp.
Restart in macOS
In Windows on your Mac, do one of the following:
Restart using Startup Manager: Restart your Mac, then immediately press and hold the Option key. When the Startup Manager window appears, release the Option key, select your macOS startup disk, then press Return.
If you’re using a portable Mac with an external keyboard, make sure you press and hold the Option key on the built-in keyboard.
Restart using Boot Camp Control Panel: Click in the right side of the taskbar, click the Boot Camp icon , then choose Restart in macOS.
This also sets the default operating system to macOS.
For more information about restarting in macOS, see the Apple Support article Switch between Windows and macOS.