I don't know if MTUSUPPORT formats the hard drives we send out with C and D partitions or not. I expect D is also there.
Windows stores "temp" files all day long on the partition it is installed in... for stuff you're never aware of. These take up little bits and pieces of storage on the HDD. Then, when you import a song, Windows puts it in the largest contiguous space it can find... if one exists. If not, the file gets stored a piece here, a piece there, a chunk over yonder. This is how a file gets fragmented.
As Gary points out, the defrag reorganizes the disc volume and makes everything contiguous again. When a defragged .kma file is accessed, the HDD head doesn't have to move to all the different places where pieces and chunks are stored. They are all in one clean, continuously readable area without any major head movements.
Where files end up after defrag will ALWAYS be in the same folder. Where that folder is on the disc volume may change... and its not something you need to be concerned about, or that you can control. Defragging is something MTU did on our MTU-130 computers we use to sell back in the early '80s. It is a fact of life with computers.
Defragging monthly is an EXCELLENT idea! 