ANDROID BEST BUY

This particularly useful when you want to hide the drive that Windows create as a Recovery Partition that enables system recovery without inserting the DVD. (nearly 100MB)

You could do it by editing registry.

Type regedit in start menu, then to HKEY_CURRENT_USER > SoftwareMicrosoftWindowsCurrentVersionPoliciesExplorer > NoDrives

Change REG_DWORD value. Values for the drives are:
A = 1
B = 2
C = 4
D = 8
E = 16
F = 32
G = 64
H = 128 etc., always double the last.

To hide several drives, add values together: for example value 40 hides drives D and F

source: here