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NADN (Nearest active downstream neighbor) The next station to receive a token in a token ring.

Nanometre (nm) One thousand millionth of a metre.

Nanosecond (ns) One thousand-millionths of a second of a second (.000000001 sec.). Light travels approximately 8 inches in 1 nanosecond.

NAUN (Nearest active upstream neighbor) The station that has just sent a token to the nearest active downstream neighbor in a token ring.

NDD (Norotn Disk Doctor) A third-party utility designed to automatically repair many hard disk and floppy disk problems, including those in the drive's boot sector, FAT, and data areas.

NetBEUI (NetBIOS Extended User Interface) A proprietary Microsoft networking protocol used only by Windows-based systems, and limited to LANs because it does not support routing.

NetBT (NetBIOS over TCP/IP) An alternative Microsoft NetBEUI component designed to interface with TCP/IP networks.

NetWare A popular series of network operating systems and related products made by Novell.

Network A group of two or more computer systems linked together. There are many types of computer networks, including LANs and WANs.

Network layer The OSI layer responsible for routing packets.

Network mask That portion of an IP address that identifies the network.

NIC (Network interface card) A network adapter board that plugs into a computer's systemboard and provides a port on the back of the card to connect a PC to a network.

NMI (NonMaskable Interrupt) A high-priority interrupt that cannot be disabled by another interrupt. It is used to report malfunctions such as parity, bus and math co-processor errors.

Node Each computer, workstation, or device on a network.

Noise An extraneous, unwanted signal, often over an analog phone line, that can cause communication interference or transmission errors. Possible sources are fluorescent lighting, radios, TVs, or bad wiring.

Non-memory-resident virus A virus that is terminated when the host program is closed. Compare to memory-resident virus.

Nonparity memory Slightly less expensive, 8-bit memory without error checking, used on Macs and recently in DOS PCs.

Normal backup A full backup that sets the archive attributes of all files and folders it backs up so that later backups can sense that a current backup exists.

Normal mode The traditional method of accessing a hard drive by which the IOS reads and write to hard drives by addressing the correct cylinder, head, and sector. See CHS.

NT Hardware Qualifier This utility, found on the Windows NT installation CD-ROM, examines your system to determine if all hardware present qualifies for Windows NT.

Ntldr (NT Loader) The component of Windows NT that load the operating system on Intel-based systems.

NTFS (NT File System) The file system that is native to Microsoft Windows NT. NTFS is probably the most advanced file system available for personal computers, featuring superior performance, excellent security and crash protection, file compression and the ability to handle large volumes of data, file names.

NTSC (National Television Standards Committee) An organization that sets standards for such devices as video-capturing cards.

Null modem cable See Modem-eliminator.

NTVDM (NT virtual DOS machine) An emulated environment in which a 16-bit DOS application or a Windows 3.x application resides within Windows NT with its own memory space or WOW (Win 16 application on a Win 32 platform). See WOW.