The term workstation refers to the computers that are attached to a LAN and share the resources of the LAN. On a LAN, there can be PCs that do not have either hard disk or floppy disk drives. Such PCs are called diskless workstations. Such workstations cannot store any data or software. They access them directly from the LAN server.
A computer (regardless of whether it has disk drives or not) is said to become a node of the LAN once you attach it to the LAN.