How do I boot from an external hard drive?

I have a MacBook Intel. I attached a USB hard drive and made a partition for an system image and another for Time Machine. I did a system Restore to the Image partition. I would like to test it to see if I can back up to it. Is there a key or something that I have to hold down to be able to choose which disk to boot from (internal or external)?
also, I created the system image for the external hard drive by using the Restore command with the source as my current hard drive and the output as the external partition. There did not seem to be any other options. Is there something else I should have done?
The drive is formatted as Mac OS Extended (Journaled) and I chose the Intel set up (GUID ?).
The OS is Leopard

Is there a key or something that I have to hold down to be able to choose which disk to boot from (internal or external)?
Hold the "Option" key when booting.

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Hi there, I recently got the white screen of death (w/ circle slash) on my 13" 2009 MacBook Pro. Most people are saying that it is hard drive failure, so I am trying to boot it from an external hard drive to save some of my data before having it repaired. Unfortunately, every time I press "option" while it boots, it only shows the internal drive on the grey screen. I have my external drive connected, but it won't recognize it. What should I do?
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Welcome to the Apple Support Communities
You can only start from an external drive if OS X is installed there. If not, it won't appear as a bootable volume because there isn't any operating system inside it.
As you have a Mid 2009 MacBook Pro, it's better to start from the Mac OS X disc that came with your Mac. Insert it and hold the C key while your Mac is starting. After starting, go to Utilities menu > Disk Utility, select "Macintosh HD" in the sidebar and repair it. If you can't get it repaired, take the computer to an Apple Store.
If the hard drive can't be repaired, the only option to recover your files is to use an application as DiskWarrior, but it's expensive and it's not sure that it will work, because it may fail

How do you boot from an external hard drive if...

Thanks in advance to anyone who can offer any advice. My 24" IMAC suddenly had hard drive ****. After much investigation it has been determined that my internal hard drive has bit the dust. Instead of taking the IMAC apart and replacing the internal drive(which I know a bit about and also could get help doing)can I just replace it with an external drive and load the OS on that and boot from there? If so what exactly, step by step, would I need to do? What are the disadvantages of doing this? If this is possible it seems like an easier solution than replacing the internal drive.
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easybpw wrote:
can I just replace it with an external drive and load the OS on that and boot from there?
Yes, but it's not recommended for long-term use.
If so what exactly, step by step, would I need to do?
First, make sure the drive will boot a Mac. Most will, but some won't. If it's a Western Digital, check here: http://wdc.custhelp.com/cgi-bin/wdc.cfg/php/enduser/stdadp.php?pfaqid=1787. But note the disclaimer that they don't support it +*at all.+*
If you're reasonably sure the drive is capable of booting your Mac, you need to format it. Start up your Mac from the Install disc (insert it, and hold the "C" key while starting up). After selecting your language, select Utilities, then +Disk Utility+ from the menubar.
Select the drive, select the top line (with the make and size), click the Partition tab and select 1 Partition from the the pop-up menu under +Volume Scheme,+ unless you need more than one.
Give it a name under +Volume Information,+ and select +Mac OS Extended (Journaled)+ for the Format unless you're certain you need Mac OS Extended (Case-sensitive, journaled). Click the Options button below the box, and select GUID (that should be the default, but make sure), and click the OK button, then Apply. That should only take a few moments. Quit Disk Utility and you’ll see the Utilities menu again.
Quit that and proceed with the installation to the new drive. When done, I think it will reboot automatically from the external; if not, start up while holding down the Option key, which will give you the +Startup Manager,+ where you can select the desired drive.

My Macbook air flash had gone for a month and I saw Apple's Macbook air flash storage drive replacement program. I'm not sure whether that program is still available for the broken device or not. Now, I'm booting from the external hard drive. Thank you.

My Macbook air flash had gone for a month and I saw Apple's Macbook air flash storage drive replacement program. I'm not sure whether that program is still available for the broken device or not. Now, I'm booting from the external hard drive. Warranty has gone in October 2013..
I want to send back my macbook air back to apple store. The problem is that I bought it from US and now, I'm using it in Myanmar. If the program is free of charge for my device, it's worth trying to send back to US. Since mine is broken, I'm afraid Apple will take charges for reparing.
So, if anyone having the same problem as me, I would like to get suggestion....
Thank you!!

I have no idea about how to handle the international aspect of your question.
But here is the Apple writeup about the problem and the remedy. Maybe that will help you.
http://www.apple.com/support/macbookair-flashdrive/

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Hi,
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Hi!
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How do I reboot from an external CD?
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Hi Chris.
What is the version of the OS on the computer and what is the version of the OS Disc that you have inserted?
Make sure you have inserted the same version of the OS disc that is currently running on the computer.
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Gop's.

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2) What equipment would I need to do it?
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WARNING: Think twice before deleting any partitions; do not delete any partitions on your internal drive.
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I purchased a 500GB external hard drive in hopes of: 1. creating a bootable backup copy of a freshly installed version of Snow Leopard, and 2. a backup of files which I don't want on my Macbook (ie. school files from 8 years ago).
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miceblue425 wrote:
I purchased a 500GB external hard drive in hopes of: 1. creating a bootable backup copy of a freshly installed version of Snow Leopard, and 2. a backup of files which I don't want on my Macbook (ie. school files from 8 years ago).
Yes.
If I divide the external hard drive into 2 partitions, can OS X still boot from a partition? I heard from somewhere that OS X can only boot a volume, but not a partition...
Two names for the same thing: partition = volume.
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How do I boot from an external hard drive?

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