Wikipedia has plenty to say on what a Master Boot Record is.

For brevity, I'll just say that it is a chunk of 512-bytes that 'optionally' sits at the start of your hard-disk (or in our case, USB stick).

Its job is to describe where to locate partitions on your disk.

For example, if your 1000MB disk has been split into multiple partitions of C: (300MB), D: (500MB) and E: (200MB), the MBR tells your OS, “Hey, you can find C: drive at this location on the disk and its size is this much, also you can find D: on that part of the disk and its size is that much, etc”.

Now, the reason why I referred to the MBR before as being 'optional' was due to the following case.

What it if we just want a single partition to expand the entire disk's contents. Well, there are two ways of specifying this:

• Have an MBR that specifies just a single partition that spans the entire disk
• Omit the MBR, and just let the single partition span the entire disk (including the first 512 bytes where the MBR would have been)

Yeah, good question, and I can't give you a definitive answer on that. My best educated guess would be that due to the C64 mini running on a stripped down version of Linux, perhaps one aspect of this 'stripping down' was in the amount of support for file-systems.

I believe a fully-fledged Linux install wouldn't have any such trouble reading any FAT32 USB stick, regardless of whether it had an MBR or not. So for now, my suspicions lie in the 'stripped down' nature of the current OS.