Converting C: to \\.\PhysicalDrive0 :

• CreateFile from \\.\C:
• call DeviceIoControl with VOLUME_DISK_EXTENTS and read DiskNumber from first VolumeExtent

Reference:

• Naming a File
• Naming a Volume

Alternatives:

• QueryDosDevice
• FindFirstVolumeMountPoint

Discussions:

• How to get the PhysicalDrive number which the logical drive locate
• Directly reading/writing a HDD
• Getting the unique volume name for an unmounted drive