Filed under: How-tos, Tips and tricks, Odds and ends, Mac 101
Mac 101: Yes, Intel Macs can be booted from an external USB drive
More Mac 101, our ongoing series of tips and tidbits for new Mac users.
Update: As the comments point out and Low-End Mac confirms, support for USB booting was present in the Mac OS 9 era with the introduction of dual-channel USB in 1999, available first on the slot-loading iMac and one model of the AGP PowerMac G4; however, your mileage and performance may vary when trying to get these machines to boot Mac OS X from USB devices (as has been previously reported on TUAW). Our apologies for the error!
When I wrote my post Tuesday about booting a Mac off an external USB hard drive, I was surprised how many people followed up to tell me that it wouldn't work, and that I needed a Firewire drive to externally boot a Mac.
While [much] older machines did indeed need Firewire for bootable external media, that is no longer true. Since the release of the Intel Mac computers [and well beforehand -- see update above], and with Mac OS X 10.4.5 or later, you can start up from an installed system on a USB hard disk. Here's the Apple support document that tells you how to do it.
I didn't think it was possible either, and when I bought my MacBook Pro last year, I was wishing I could boot from a USB drive because of the easy availability of inexpensive storage. A little online research revealed the obscure truth. USB booting generally works fine from a bus-powered portable drive as well as a powered USB desktop drive. In my case, I booted up just fine from a portable with no external power supply. Check the support document linked above for more details.
So have at it -- either install a clean version of Leopard or Tiger on the drive, or use your favorite bootable-backup utility to clone your existing install to the USB volume. It's a good thing to know as Apple seems to be determined to bury Firewire on the lower priced laptops it sells.
It is also possible to boot an Intel Mac from a USB flash drive. That is a bit more involved, and there are several methods. One is Das Boot, a free utility from Sub Rosa that allows you to convert original disks from DiskWarrior, Drive Genius, TechTool Pro and others to a flash drive. Let Google be your friend on this. Many people have put their favorite rescue utility on a bootable flash drive to save them from any problems in the field.
Before you ask; no, USB does not support target disk mode -- a sore point for MacBook Air and unibody MacBook owners.
Thanks to Dave and others who wrote in asking about this, and thanks to many readers who wondered about the ability of older PPC Macs to do this as well.
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Reader Comments (Page 1 of 3)
Orrello said 11:09AM on 12-18-2008
Thanks, great tip!
What exacly is "target disk mode", and what is the difference between booting an USB drive instead of a disk in 'target disk mode'?
Reply
Simon Arch said 11:31AM on 12-18-2008
Target Disk Mode lets you boot a computer as if it were an external drive. This is very useful if you're moving from an old computer to a new one. You boot the old Mac in TDM and plug it into the new one. The new one will see the disk and you'll have access to all your files. This is also how the migration assistant does its thing.
antiorario said 11:31AM on 12-18-2008
A Wikipedia link is worth more than a thousand words :-)
http://en.wikipedia.org/wiki/Target_Disk_Mode
Dave said 11:11AM on 12-18-2008
I've booted an old iMac (Blue Dalmation if I recall) with an external USB drive over USB 1.1. It was slow, but it certainly worked.
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Mario said 11:25AM on 12-18-2008
No you didn't. Old Power PC's can not boot from USB. Intel's on the other hand can boot from USB as long as the drive is formatted as GUID Partition. I have been doing this from the first time I got a intel Mac to dual boot my mac mini into tiger and leopard. However I know plenty of people who don't know that you can still.
Joshua L Smith said 11:58AM on 12-18-2008
While I can't vouch for his iMac story; I routinely boot my PowerBook G4 1.25ghz off of a USB drive.
Chad said 1:31PM on 12-18-2008
@Mario You most certainly can boot PowerPC Macs off a USB drive
Michael Rose said 2:56PM on 12-18-2008
Dave is right and we were wrong. See update to the post.
geo said 6:52PM on 12-18-2008
Sorry Mario:
You most definitely CAN boot some old USB 1.0 equipped iMacs with a usb startup drive. I've done it many times.
Also, I am writing this email from an intel iMac booted from an extenal usb 2 drive runninf OSX 10.4.11. Drive is formatted HSF+ with journaling ( not GUID) and starts up perfectly. Trick is to clone OSX from mac or other drive with startup system. You cannot install OSX 10.4 or 10.5 onto an external disk formatted HFS+, though.
Todd said 11:13AM on 12-18-2008
I will back you up on this because I have booted my Macbook Pro from an external USB drive that I had imaged my system over to.
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james kachan said 11:19AM on 12-18-2008
I boot from an eSATA drive via my macbookpro's express32 slot
:)
funny that it actually benchmarks faster this way than my internal 7200rpm drive.
* a word of warning though.
not all eSATA express cards have native support for OSX the first one i had wouldnt be seen on boot.
so be careful what you get.
cheers!
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lanejasper69 said 1:54PM on 12-18-2008
Hey James, I have a SD card reader in my Express Slot, can/do you think I could install OSX to the 8GB SD card and boot from that? I was wondering this the other day and then saw your post. The Card reader is a SIIG ExpressCard 11-in-1 R/W and says 34 RoHS on it....any advice links etc. would be greatly appreciated!!!!
Thanks!
Lane
Tyler said 11:19AM on 12-18-2008
You do not need any special software to make a bootable USB thumb drive. Just clone the Leopard Install DVD to an 8gb usb thumb drive and your mac will boot from it without any issues... at least i have done it without issue...
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Simon Arch said 11:33AM on 12-18-2008
Good to know! I'm planning on buying an 8gb thumb drive for this exact purpose, but I wasn't sure if it could actually be done. I couldn't think of a technical reason why not, so it's good to have outside confirmation it's possible. :)
Jamie Phelps said 11:26AM on 12-18-2008
How would a USB drive support Target Disk mode? Computers support TD mode, and no Mac supports TD over USB, if that's what you meant.
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jeckyll said 11:27AM on 12-18-2008
You can even boot from an iPod! At least a classic one.
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mallzombie said 11:29AM on 12-18-2008
Hmmm... external hackintosh?
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roycifer said 2:15PM on 12-18-2008
the point of a hackintosh is to run OS X on a non-apple PC... so theres nothing hackintosh about booting an external OS X via a mac.
ZeroCorpse said 11:35AM on 12-18-2008
You know, when Apple introduced the new MacBooks and everybody was screaming about the lack of firewire and being able to use Migration Assistant or boot from an external drive, I was telling people in online forums this very thing and they DIDN'T BELIEVE ME.
I've been restoring and migrating via USB for years now. USB 2.0 is almost as fast as firewire when it comes to migration or booting from external. It's a perfectly viable option. This is why I rarely used the firewire port on my white Santa Rosa MacBook, and why I don't miss it at all on my aluminium MacBook.
Now, if only Windows would be smart enough to boot from an external drive. . .
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paxswill said 1:55PM on 12-18-2008
I have to take issue with your assertion that USB2 is about as fast as Firewire. When I got a triple interface drive a couple months ago, I decided to benchmark each of the interfaces on it. USB2 had a maximum throughput of 256Mbps, while Firewire 400 had a max of 314Mbps (FW800 had a max of 617Mbps). That's a real difference to me, and helps a lot when I've had to restore from Time Machine.