this pc used to only have C: and D: .. then one of my other pc broke down, I got the HDD from that pc and put it into this one... causing F: and G: to appear .. but I can't remember when the System Reserved E: appeared.
my thoughts is, since G: is not really a part of the boot disk, then it could be renamed safely to E: ... or maybe this would affect system reserved in some way, since it's also named E: ??
after reading the comments. I suppose, leaving things alone would be better.