Apple can sometimes make small changes that have unexpected consequences.

Take Partition Schemes, for example.

This is the kind of thing most Mac users never think about. You buy a drive, plug it in, drive comes up, things work.

Done.

What you probably don't know is that most drives came partitioned and formatted for Windows, even when the drive is listed as "Mac Compatible", typically using Master Boot Record as the partition scheme and FAT32 as the format.

Before OSX 10.4.6 or so, this wasn't a big deal, at least for SuperDuper! Since FAT32 isn't appropriate for storing Mac files with full fidelity (and has various other issues, like file size limits, etc), we would instruct the user to erase the drive, using HFS+ (Mac OS Extended) as the format. Disk Utility wouldn't allow HFS+ volumes to be hosted on Master Boot Record partitioned drives, and so the user would need to select the drive, rather than the volume, and erase that way. No big deal.

Then, the Intel Macs came out, and with them, 10.4.6.

To help with something-or-other (probably to allow HFS+ and FAT32 volumes to be hosted on the same drive in separate partitions for Boot Camp users), Apple decided to change Disk Utility so that it allows HFS+ volumes to be hosted on Master Boot Record partitioned disks. Which I'm sure didn't seem like a big deal: in fact, it's quite convenient, and had probably been requested as a feature over the years.

All that's great, except for one thing: Macs don't support starting up from Master Boot Record volumes.

This is clearly not a big deal for most users. But, for SuperDuper! users (and, I'm sure, for those who use similar applications) it's been a big problem: drives that look like they should act as startup volumes won't, and the reason is really obscure.

Suddenly, users who used to use Disk Utility to erase a drive now have to head to the Partition tab (which doesn't even appear if you select the volume instead of the hosting drive), click Options, understand the 3 partition types, and partition their drive appropriately.

So, this one small change -- allow HFS+ volumes on Master Boot Record partitioned drives -- ends up having a pretty big impact on users with external drives. This is mostly due to its implementation (and lack of documentation).

Worse, users aren't steered to the right choice by Disk Utility. In fact, the default is to do the absolutely wrong thing for most: retain a Windows partition scheme.

This probably hasn't had much of an impact on Apple's support, but it's sure hurt here!