That is true for most disk operating systems. Some O/S are designed to work without disk access. In that case, the speed of the drive only affects initial startup (and shutdown if data is stored on the drive for future sessions.) There are some Linux distros that are designed for operation without disk I/O. Others can be configured to minimize or eliminate disk I/O.The cheap/slow NAND flash that they use in USB flash drives makes it a bad choice to run an operating system on. Doesn't have anything to do with being a VM.