Adding another internal hard disk drive (whether SSD or conventional) is normally very easy to accomplish if you have a spare SATA or M2 port available on your motherboard.
In a mid-tower ATX case there are usually plenty of spare bays to which the physical drive can be installed.
Let's say you have an older conventional hard disk drive as your current C: Drive/ boot drive and you're running out of space.
What you can do is purchase a larger capacity HDD or SSD to replace it as your boot drive C:\ (whilst retaining the existing drive for continued use as a data storage drive. It (the old drive) would then be designated Drive D: or E:, depending upon what else, including DVD drives etc., might already be there.)
Assuming your current boot drive is functioning well (i.e. no OS issues, but you may well be running out of physical space) then to save having to do a complete operating system installation, plus reinstalling all of your current applications including T:ANE and TS12 etc. you can clone the old drive in its entirety (using one of the utilities mentioned earlier) and thus transferring the whole kit and caboodle onto the shiny new, higher capacity disk drive.
You can even use a smaller, faster SSD drive if you prefer, but the cloning becomes a tad more complex as you have to choose which applications including the OS can be safely fitted on the new drive and then which items will be left on the old source drive because they won't all fit. Obviously, it is best to go for a larger capacity and faster SSD than the existing drive though, if at all possible.
When I bought my Samsung EVO SSD it came with migration software for cloning the original drive (an older, smaller capacity SSD) and the operation took only a few minutes.
(Helps to have a USB 3.0 to SATA adapter available for this process, so you can clone the old drive to the new one before physically installing it into your case.)
Once cloned, insert the new drive into your case and unplug the old one temporarily so that you can boot to the new disk.
Assuming all has gone well, you can then reattach/ reinstate the old internal hard drive, which will now have a new drive letter/ logical disk drive name other than C:\.
After thorough testing of the new drive's operation, and installed applications brought over, you can then safely format the old one (after backing it up to your external drive once again just for good measure) and re-purpose it as a dedicated game drive or relegate it to additional data storage space.
