The rules regarding quoting of pathnames with spaces are esoteric and depend on the surrounding commands, exact version of CMD (the DOS command shell/interpreter), extension settings, the phase of the moon

, etc.
If you
were to quote the pathname (good practice, needed or not, for silly paths containing spaces, or when you don't know what might be used in the future), the leading drive letter should be inside the quotes, i.e.
"C:\DSDPlus Main".
However, also note that, the way CMD works, the command
CD "C:\DSDPlus Main", if executed while your current drive is other than C:, has the effect of changing the working directory on the C: drive, but not your current directory. If you then type
C:, your working directory will become that directory you gave in the CD command, on the C: drive. I.e., it takes two steps to set the current working directory to an arbitrary drive letter and path. Normally, you change to that drive and then the path within it:
Code:
X:\cur_work_dir_on_x> C:
C:\cur_dir_on_C> CD "C:\DSDPlus Main"
C:\DSDPlus Main>
(The part to the left of the '>' is the current working drive and directory)
Yes, if your current working directory is on C:,
C:\cur_dir_on_C> CD C:"\DSDPlus Main" also works, as does
C:\cur_dir_on_C> CD C:\DSDPlus Main, as does simply
C:\cur_dir_on_C> CD \DSDPlus Main.
You can technically do it the following way, too – it's just not good practice, since you don't see confirmation that it did what you expected until you switch your working directory to the C: drive:
Code:
X:\cur_work_dir_on_x> CD "C:\DSDPlus Main"
X:\cur_work_dir_on_x> C:
C:\DSDPlus Main>
I hope that makes sense.