The Motivation

OSX can do everything I want from day to day, but occasionally I want to play some San Andreas. Bootcamp and Windows should have had me playing Windows games on the Mac. Sadly, Bootcamp refused to partition my internal disk so I was stuck with no Windows and no San Andreas.

A ray of hope was the idea of installing Windows onto a blank external disk. Windows is not supposed to run from an external disk but it has been done before. The brave souls who made this work in the past still needed to re-partition their disk with Bootcamp though, something that wasn’t an option for me.

It turns out that it is possible to install Windows to a USB disk without using Bootcamp at all. Here’s the recipe:

Ingredients

• An Intel Macintosh - This procedure was tested on a first generation MacBook.
• A USB2 hard drive - I used a Welland “Sun Bright” chassis with a Samsung IDE disk inside.
• rEFIt - A boot manager for EFI computers (like Intel Macs).
• A Windows XP install CD (SP1 or higher).
• A tool for extracting and editing ISO images. I used MagicISO (a commercial Windows application sadly).
• The Microsoft CAB SDK.

Procedure

This is the process I used. Step two is a pretty complex sub-procedure. It was produced by some serious Windows Wizards and is the core of what we are doing here. The rest is easy, these guys are good.

1. Install rEFIt.
2. Create a modified Windows XP install CD with support for USB installation. This is a long procedure. Follow the link, complete steps 1-9, then come back here.
3. Power off.
4. Disconnect your internal hard drive. For a MacBook, use this guide.
5. Start your Mac, holding “c” to boot from the XP install disc.
6. Step through the Windows text-mode installer until your system reboots.
7. Power off.
8. Replace your internal drive.
9. Power on.
10. Tell rEFIt to boot Windows from the USB drive.
11. Follow the Windows graphical installer. Answer yes to any questions about unsigned drivers. The system will reboot again
12. Tell rEFIt to boot Windows from the USB drive.

Now you are running Windows from the USB drive.

Macintosh Drivers (and the USB trap)

At this point, I must confess that I cheated. I did install the Bootcamp drivers into my XP install and I believe there is a serious trap here. The Bootcamp driver set contains drivers for the Intel USB controller, which it naturally tries to install. It pops up an uncertified driver warning before installing them. I told it not to install the USB drivers, since the entire operating system was hanging off that device. Replacing the drivers at that point seemed like a very bad idea to me.