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.

Last month, I wrote a post about Apple certifications in general. Today, I'll focus on Mac OS X certifications.

If you're a Mac geek who wants to make a living troubleshooting Macs, these are the certifications to get because they are your ticket to becoming a member of the Apple Consultants Network (ACN). ACNs can build a relationship with their local Apple store and get references for work that can't be performed by Genius Bar techs, and they're listed on the Apple Consultants Network website. The rest of this article is after the break.

TUAW blogger Steve Sande is an Apple Certified Technical Coordinator and volunteers as the South Central US Regional Champion for the Apple Consultants Network.

Along with the 10.5.4 update, Apple has just released Security Update 2008-004 for users of Mac OS X Tiger (10.4). According to Apple, the update "is recommended for all [Mac OS X Tiger (10.4)] users and improves the security of Mac OS X." You can download this update for the following systems:

• Security Update 2008-004 (PPC)
• Security Update 2008-004 (Intel)
• Security Update 2008-004 Server (PPC)
• Security Update 2008-004 Server (Intel)

The update is available through Software Update (Apple menu > Software Update) or by downloading the installer packages by clicking the links above for your system. Apple has provided a support article for more details on this update.

Thanks to everyone who sent this in!

Are you dying for a sneak peek at Leopard, the next incarnation of OS X? If so, book a ticket for San Francisco in mid-August. Apple has announced, on its site and by email to customers, that it will offer a preview of OS X Leopard at  WWDC 2006, scheduled for August 7-11.

The Apple site briefly describes five WWDC session tracks -- Application Technologies, Development Tools, Graphics and Media, Information Technologies, and OS Foundations --  but doesn't provide details about specific sessions. If you're considering going, try to get your boss to pick up the registration fee, which is a stiff $1295-$3500 before June 23 and even more after that date. If you're a student, don't overlook Apple's Student Scholarship Program. We told you before -- but it's worth a reminder -- that applications for a free WWDC ticket through that program are due on April 28.