NetBIOS (Network Basic Input/Output System) was originally developed by IBM and Sytek as an Application Programming Interface (API) for client software to access LAN resources. Since its creation, NetBIOS has become the basis for many other networking applications. In its strictest sense, NetBIOS is an interface specification for acessing networking services.

NetBIOS, a layer of software developed to link a network operating system with specific hardware, was originally designed as THE network controller for IBM's Network LAN.

NetBIOS has now been extended to allow programs written using the NetBIOS interface to operate on the IBM token ring architecture. NetBIOS has since been adopted as an industry standard and now, it is common to refer to NetBIOS-compatible LANs.

It offers network applications a set of "hooks" to carry out inter-application communication and data transfer. In a basic sense, NetBIOS allows applications to talk to the network. Its intention is to isolate application programs from any type of hardware dependancies. It also spares software developers the task of developing network error recovery and low level message addressing or routing. The use of the NetBIOS interface does alot of this work for them.

NetBIOS standardizes the interface between applications and a LANs operating capabilities. With this, it can be specified to which levels of the OSI model the application can write to, making the application transportable to other networks. In a NetBIOS LAN enviroment, computers are known on the system by a name. Each computer on the network has a permanent name that is programmed in various different ways.

PC's on a NetBIOS LAN communicate either by establishing a session or by using NetBIOS datagram or broadcast methods. Sessions allow for a larger message to be sent and handle error detection and correction. The communication is on a one-to-one basis.

Datagram and broadcast methods allow one computer to communicate with several other computers at the same time, but are limited in message size. There is no error detection or correction using these datagram or broadcast methods. However, datagram communication allows for communication without having to establish a session.

All communication in these enviroments are presented to NetBIOS in a format called Network Control Blocks (NCB). The allocation of these blocks in memory is dependant on the user program. These NCB's are divided into fields, these are reserved for input and output respectively.




NetBIOS is a very common protocol used in todays enviroments. NetBIOS is supported on Ethernet, TokenRing, and IBM PC Networks. In its original induction, it was defined as only an interface between the application and the network adapter. Since then, transport like functions have been added to NetBIOS, making it more functional over time.

In NetBIOS, connection (TCP) oriented and connectionless (UDP) communication are both supported. It supports both broadcasts and multicasting and supports three distinct services: Naming, Session, and Datagram.