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: 
Deduct some available memory by creating a ramdrive, which will not impose the additional CPU cycle burden of a VM.

Ramdrives, or ramdisks, are discussed herein for [Windows](https://superuser.com/questions/1091597/create-a-ram-drive-in-windows-10-to-improve-a-modded-instance-of-tes-v-skyrim), [Linux](https://unix.stackexchange.com/questions/290175/how-to-specify-memory-region-for-ramdrive), and [MacOS](https://apple.stackexchange.com/questions/55794/why-do-mac-os-x-ramdisks-appear-to-be-limited-to-550mb-and-how-can-i-change-this).

For Windows, one Open Source app is [ImDisk](https://sourceforge.net/projects/imdisk-toolkit/), but there are many other choices.

Linux includes [tmpfs](http://man7.org/linux/man-pages/man5/tmpfs.5.html) but you have multiple other options here as well, such as the use of `mem` as a [command-line option in the kernel](https://www.kernel.org/doc/html/v4.14/admin-guide/kernel-parameters.html), as noted in comments below by [Austin Hemmelgarn](https://superuser.com/users/751187/austin-hemmelgarn).

For MacOS, you don't even need to create the ramdisk to obligate the memory; instead, as per the aforementioned link, do 

```
hdiutil attach -nomount ram://1165430 /dev/disk4

```
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.