A Ramdisk is where a portion of your system memory is set aside in such a way that the operating system thinks it's a disk drive. The advantages are performance based: DRAM is faster than NAND flash and much faster than a hard disk drive. Disadvantages are that it's not a permanant storage (power off and the contents are wiped clear), the contents of the ramdisk need to be loaded with each boot, and you lose a portion of the system memory.
This doesn't happen by default or within Windows itself - you must have an application installed that has set this up. Have a look to see what programs you have running during boot up (CTRL+shift+ESC to start up Task Manager and go to the Start-up tab). Given that it would seem that this has installed without your knowledge, I'd personally advise you to disable it (and perhaps uninstall it).