Their ad kind of hides it from you, making you think you can have up to 256GB...
But to use 256GB you need to have 256GB spare!
You can only make a RAM disk as big as your actual RAM, less what you need to run the OS normally.
Theoretically, you may be able allocate more RAM to a RAM disk than you own, but you would be completely defeating the object as your OS would then be paging the excess back to your regular HD/SSD, making the entire process slower than before you set up the RAM disk.
From their web page... hidden away down the bottom...
What are the requirements to run DimmDrive?
A 64bit PC running Windows 7 or above, with any CPU, with at least
more RAM than your OS+programs use. DimmDrive can use any amount of
RAM, from 256MB to 256GB.
How much RAM do I need for DimmDrive?
The more RAM you have, the better. It really boils down to what you are using it for. Also,
DimmDrive has a feature we call “Less RAM?” which enables you to
selectively pick which files in a game you want to go blazing fast.
This feature alone can take a 10GB game and slim it down to 4GB-ish by
removing video/intro files, sound files, and other non-essential files
that do not need to go blazing fast. If you are doing light gaming, we
recommend having 6GB+ RAM. If you are doing heavy gaming, we recommend
8-16GB. If you are using DimmDrive for things like Audio/Visual
scratch disk, you typically will want 2GB or more for that. As with
everything PC related, the more RAM, the better!
A RAM disk isn't "magic", though the ad makes it sound like it is. It's a good way of quickly being able to load resources already saved to it, as they state.
For any RAM disk, you set it up, then copy data to it. If the RAM disk is put away without saving its contents back to HD, then everything is lost.
As far as I can see, their 'special ingredient/selling point' is just that they are periodically saving back to HD in case of power-loss, so that no data is lost.
They also appear to have some kind of data slimming system, presumably they're doing something like aliases/hard/soft links back to the larger files to make it appear to the game that they are all in the right place.
I use RAM disks all the time on Mac, copying out & back in a similar way as they describe - but I have 64GB RAM to play with, so size isn't an issue. I don't actually have any fail-safe on mine, but I'm using ephemeral data which would not be a disaster if I lost a few hours' work.
Unfortunately, I have no ides how you would write that for Windows, sorry.