If you want to have new drive letter for example D or E without adding new physical harddisk, you can do by shrink the volume of C drive and make new partition for new drive.
Same as in Windows 7, to divide the partition and create a new volume in Windows 8, you can do easily without using additional software/application.
• From the Desktop, select File Explorer, then right click at Computer
• Then click Manage.
Computer Management window will appear
• On the Storage menu, select Disk Management
You will see the volume or partition to be divided (in this case : C)
• Select and right-click on it (C partition), then choose Shrink Volume.
• You can input the size volume to be shrink.
• If you are confused with the amount to be input, leave it as is, no need to change anything.
• Click Shrink to continue.
Then you will see the new space, unallocated space. From this unallocated space you can create new volume/new drive letter (D, E, etc).
To create a new volume:
• Right click on the unallocated space
• Select New Simple Volume
Then the wizard will appear, just click: Next..next
• Enter the volume to be created, or leave it as is for the maximum size.
Click Next
• Select the drive letter, for example drive D, E, etc., click Next
In the next wizard
• Choose Format this volume with the following setting.
• Usually just change the volume name, or you can leave it as is, because it can be easily renamed later.
• Give a tick on the Perform a Quick format, for rapid format process. then click Next.
After the process, you will see the new hard disk drive in Computer menu.