With mosix you can start a process on one machine and find out it actually runs on another machine in the cluster. Each process has it own unique home node (UHN) where it is created.
Migration means that a process is splitted in 2 parts, a user part and a system part The user part will be moved to a remote node where the system part will stay on the UHN and. This system-part is sometimes called the deputy process, this process takes cares of resolving most of the system calls. Mosix takes care of the communication between those 2 processes.
Both Mosix and openMosix provide a cluster-wide file-system (MFS) with the DFSA-option (direct file-system access). It provides access to all local and remote file-systems of the nodes in an Mosix or openMosix cluster.