[Device with Removable Storage show Drives E: F: G: H: I: ?]

hello,

when I open the My computer option under the 'Device with Removable Storage'

option I've five more drives i.e E: ,F:,G:, H: and I:.
when I insert a CD or DVD it is shown in E: but when I insert a pendrive or MMC
or a mobile cable to computer some more new drive come on the screen like J: ,K: etc etc

Then what these F: G: H: I: drive for? If I disable them from 'safely remove hardware' they will disappear but if i restart the system they reappears.
Then what they functioning if they if they don't even work for any external device. Are they using any memory of the system?

help plz
thanks