Method 1 Computer Management:
Open Computer Management (compmgmt.msc)
Expand Storage
Click on Disk Management
Right-Click on your hard disk(s)
Review the General tab and the Location field
Method 2 Registry Editor:
Run the registry editor (regedit.exe)
Drill down to the following path:
HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\Scsi\Scsiport0
Use the "identifier" and "DeviceType" values, determine which entries are for DISKS and which are for other devices such as CD-ROMS, tapes, scanners, and so forth.
Scisbus0
Targetid0 > Logical Unit Id 0 look at identifier and type.
Targetid1 > Logical Unit Id 0 look at identifier and type.
Targetid4 > Logical Unit Id 0 look at identifier and type.
Scsibus1
Targetid0 > Logical Unit Id 0 look at identifier and type.
Targetid1 > Logical Unit Id 0 look at identifier and type.
Targetid2 > Logical Unit Id 0
...
Find each DeviceType:REG_SZ:DiskPeripheral entry under the Targetid#\Logicalunitid0. Each one found equates to a drive in Disk Administrator and also to a \device\harddisk number.
To find \device\harddisk6 find the 7th DiskPeripheral (zero through five)
More: http://support.microsoft.com/en-us/kb/159865
Method 3 Diskpart:
Open and elevated command prompt/PowerShell window
Type diskpart and press enter
Type list disk and press enter (you can also type list volume for a list of all volumes)
Review the output
Method 4 WMI in PowerShell:
Open and elevated PowerShell window
Type gwmi win32_diskdrive | select * and press enter
Review the output
Method 5 WinObj:
More: http://www.mysysadmintips.com/windows/clients/472-find-which-drive-letter-corresponds-to-device-harddiskvolume