Is there any way to configure Windows 7 to make two hard drives act as one (without using RAID), so hard drive 1 and hard drive 2 would share a single drive letter?
Can this be achieved natively in Windows, or do I need some external software?
By far the easiest solution that technically meets the requirement is to mount the second drive as a subdirectory of the first. I.e. the second drive could be
If you do want to share space, you're talking about RAID-0 (or JBOD, Just a Bunch of Disks). Windows can do this without extra hardware. You'll use
First, convert both disks to "dynamic" disks. Right-click the disk and choose "Convert to Dynamic Disk".
Next, you can create a volume on one disk and then extend it to the second disk. There's one restriction: you can't do this with the Windows boot disk itself. (That makes sense: you're not using hardware for this RAID solution but Windows, so Windows has to be loaded before this works)
If you are using NTFS for your file systems, you may want to look into Junction Points.
It then goes on to list some examples. To mount a drive as a subdirectory of another drive, as MSalters suggests, the appropriate example would be:
An excellent example of this is if you have a small SSD boot drive, but want to move a huge game you're not currently playing off your SSD and onto your big hard drive so you can install another game. First you move the folder to the other drive and create a junction point where it was to where it is now.