Diskless workstations:

   Most people assume that the operating system is stored on a disk that is connected directly to the computer, but this is not necessarily true. If the computer is attached to a network, it may obtain its programs, including the operating system, from another computer on the network. This has led to the concept of the diskless workstation, a personal computer that relies completely on the network for its data and program storage and access. Diskless workstations are also known as  thin clients. The size of the kernel and the particular services provided within a kernel vary from one operating system to another operating system, depending on the organization and capabilities of the system, as well as by the type of system.