Many implementations use hardware to do the mapping between the FireWire "Physical Memory Space" and device physical memory. Among these, are those used by PCs and Macs, especially those using OHCI. In this case, the operating system is not involved in the transfer. This allows for high speed transfers with a low latency and avoids that the data is copied around unnecessarily. It can however be a security risk if devices that are not trusted are connected to the bus. Installations where security is a concern will therefore either use newer hardware, which use virtual memory to map the Firewire Physical memory space, or disable the mapping the OHCI does. They might also disable the whole Firewire subsystem, or not provide Firewire at all.