Each Coda client sees the Coda File System as a single tree, /coda. In reality this tree is an illusion supported by System Control Machine (SCM), several dedicated file servers, and a local area network. One of the servers may double as the (SCM). Figure 3-1 illustrates the server organization.
The Coda architecture recognizes three types of machines, clients, servers and a system control machine (or SCM). Client machines are typically single-user workstations used to access shared information. These machines are not trusted by servers except for the duration of a login session by an authenticated user. Server machines are secure, trusted machines whose purpose is to service client requests for shared data. As the custodians of shared information, servers must require authentication of each user before releasing shared data to the users client workstation. The third machine type is the system control machine (SCM). The purpose of the SCM is to provide a single point of control for ease of administration. Logically, the SCM is distinct from the servers, but, physically, the SCM can also act as a server.