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.

Are you looking for a tiny portable hard drive for doing Time Machine backups on the road? I do a lot of traveling with my MacBook Air and don't often get a chance to back it up to the 1 TB monster at home. Although there are several other diminutive hard drives on the market, when I saw the My Passport Studio line of portable drives announced today by Western Digital, I ordered one. After all, the case matches my AirBook!

Available in 160 ($129.99), 250 ($189.99), and 320 GB ($219.99) flavors, My Passport Studio drives are about 3.2" x 5.0" x .71" (81mm x 127 mm x 18 mm) in size and weigh a featherweight 6.4 ounces (.18 kg). The drives are bus powered -- USB 2.0 or FireWire 400 -- so there's no need to tote a power brick when you're traveling. They're formatted as HFS+ Journaled, requiring Mac OS X 10.4.11+ or 10.5.2+.

The drives are available from Western Digital, and through a variety of online and brick-and-mortar stores. The 250 and 320 GB drives are showing back-order status.

Thanks to Denver pal Mike for the phone call tip this morning!

Two days after Apple TV Hacks published the much sought-after USB hard drive hack for the Apple TV, the site is making a call for help to polish the modification. For now, the hack isn't for the faint of heart - it requires some mucking around at the command line, not to mention an Intel Mac to apply the patch (i.e. - PowerPC Mac and Windows owners seem to be out of luck for now). It also appears that the hack is confirmed to not work on Apple TVs that have had their software updated to the 1.1 YouTube edition.

Specifically, Apple TV Hacks is looking for help to simplify the hack's process and, ideally, bundle it in a GUI to make it a lot easier for all users to apply. Compatibility with the 1.1 Apple TV software is also on the todo list, since reverting one's Apple TV back to the original software and losing all the new features isn't the first thing most users want to do.

If you have any skills with helping out on hacks or bundling them into a GUI, or if you know a developer who might, send them over to the Apple TV Hacks post to see if they can lend a hand.

We are very pleased to report that Apple TV Hacks has published the long-anticipated USB hard drive hack for the Apple TV, allowing users to plug in an external hard drive to overcome the device's disappointing storage limitations. As with any hacks of this nature, however, the same 'hacker beware' policy applies: while the steps involved don't sound too difficult and this hack deals entirely with software (one of the rules of the contest that started all this was that the Apple TV case would not need to be opened to apply the patch), it is entirely possible that tinkering in this way could somehow void your warranty (though I would imagine you could simply use the device's menu option to reset all settings and software to original manufacturer status to clean up evidence you've been tinkering).

Still, if any of you try this, be sure to chime in with your experience. The hack was designed and tested on the original 1.0 Apple TV software, so the crew isn't sure if it'll work with the current 1.1 YouTube edition released in June.

jarpy has an interesting post up on installing Windows XP to an external USB hard drive without using Boot Camp to repartition his internal drive. This method makes use of the Open Source rEFIt utility which we've mentioned before. The process itself looks somewhat risky (e.g. jarpy disconnected his internal drive to avoid corrupting his OS X install) and playing around with third-party boot loaders is always potentially dangerous in my opinion. However, the payoff of a USB-bootable Windows drive is rather appealing, so it might be worth a look for some of you. Proceed at your own risk. If any of you decide to get this working, please share your experiences in the comments.

[Via Digg]