Question: Our application deals with large files, say 2Gb, and accepted wisdom is users need RAM 10X dataset size. Developers have well-specced machines but some users see horrible performance which we attribute to their much lower RAM, but can't categorically prove or measure.

Is there a way on Windows, Linux, Mac to 'hide' RAM from the OS without turning it off. Ideally at run-time i.e. not BIOS? Or even a utility which will gobble a requested amount of RAM and prevent other apps using it?

Our application also makes heavy GPU demands via OpenGL which makes VMs a tricky option. I know that Parallels and VirtualBox simply don't support the OpenGL version we use, others might but are sometimes pricey.

Answer: 
There is.

On Linux, use the kernel command line parameter `mem=`. Add this option to the kernel command line in GRUB. [Reference.](https://askubuntu.com/questions/83109/kernel-mem-parameter)

Windows has the `/BURNMEMORY` and `/TRUNCATEMEMORY` boot switches. Use `bcdedit` to add these switches or [Reference](https://technet.microsoft.com/es-es/ff542290(v=vs.71)). On Windows Vista and 7, F10 gets you into a pre-boot screen where you could add it for just that session, not sure how that works with Windows 10. Use BCDEdit option if not available. [Another reference](https://www.geoffchappell.com/notes/windows/boot/editoptions.htm).
Another idea: You can configure a virtual machine with whatever amount of RAM you want and run the app in there to see how it behaves.