I want to buy RAM Disk licenses for my home PC lab. Right now my system is a Dell Precision T7910 workstation (UEFi) booting from a NVMe M.2 drive with multi OS boot menu. I will be running various 64bit Microsoft operating systems from the boot menu, including Win7, Win10, Server 2008, 2016 and 2019 (all data center versions).
I'm not sure what the RAM Disk order of execution would be:
System power-up -> UEFI boot loader loads OS selection menu -> RAM Disk runs creating non-persistent drive(s) for temporary files and Windows cache files, and creates and loads persistent user folders keeping the on-disk images frequently refreshed as well as program data (and program files?)
System power-up -> RAM Disk allocates various memory spaces for RAM drives(s) -> Boot loader menu loads -> OS selected -> images are loaded to previously instantiated RAM drives
The RAM Disk drivers are loaded and initialised by the I/O manager along with all other drives configured with SERVICE_SYSTEM_START. In other words, in a multi-boot setup you would need to install the RAM Disk separately in each OS. I also recommend installing in separate folders, because the drivers in the installation package have different signatures for different OSes.
For practical purposes you can assume that a RAM disk is initialised before any user logs on. For large disks however, there is a chance that the disk is still not present being initialised. Obviously a RAM disk can't be used to boot Windows from it or anything like that.