NetBIOS is Network Basic Input Output System which is an API used for communication between systems over LAN (Local Area Network) like Ethernet and Token Ring. It was initially developed for IBM’s machines to communicate on LAN and later on was mostly used in Windows environment for Server Message Block (SMB) for file sharing, printing which later became Common Internet File System (CIFS).
NetBIOS used NetBEUI (NetBIOS Extended User Interface) networking protocol on the LAN for communication and was replaced by NetBIOS over TCP/IP (NBT).
The systems on the LAN were given unique NetBIOS names which resolved to IP address by the WINS server (Windows Internet Name Service) which maintained records of NetBIOS names mapping to IP addresses.
NetBIOS is legacy and has been replaced by DNS which has similar and robust architecture.
NetBIOS Port Numbers
137 over UDP – NetBIOS Name Resolution (NBNS)
138 over UDP – For communication between systems on LAN
139 over TCP – For session establishment between systems on LAN
445 over TCP – Replaced NetBIOS with TCP/IP stack
RFC Reference
RFC 1001 – Protocol Standard for a NetBIOS Service on a TCP/UDP Transport: Concepts and Methods
RFC 1002 – Protocol Standard for a NetBIOS Service on a TCP/UDP Transport: Detailed Specifications