I think you are speaking about letter drive your pc shows and it can be E or F or G,that's depends on devices you have attached to your pc.
My post spoke about the letter E that symbian os assigns to your mc card in your phone os
I explain drive letters in S60 :
C:\. This drive is also called phone memory. Basically it is a flash memory where we can install applications and store our data. Unlike memory card, it is always inside our phone. So, even if we remove the memory card, our data are still there. However, note that the size of phone memory is limited.
D:\. It is the drive used to store temporary files. The contents will be deleted when the device reboots. In many cases, we don’t use this drive.
E:\. It is the drive of your memory card. Normally, this is the place where we install applications and install our data.
Z:\. This is where the ROM image is stored. It contains all the operating system’s applications and data files. Since it is read-only memory, you cannot write anything. The only way to modify the contents of Z:\ drive is by flashing the phone, for example via Nokia Software Updater
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