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NSLOOKUP Command line program in Windows used to determine exactly what information the DNS server is providing about a specific host name.

NTDETECT.COM One of the critical Windows NT/2000/XP startup files.

NTFS (NT file system) Robust and secure file system introduced by Microsoft with Windows NT. NTFS provides an amazing array of configuration options for user access and security. Users can be granted access to data on a file-by-file basis. NTFS enables object-level security, long filename support, compression, and encryption.

NTFS permissions Restrictions that determine the amount of access given to a particular user on a system using NTFS.

NTLDR Windows NT/2000/XP boot file. Launched by the MBR or MFT, NTLDR looks at the BOOT.INI configuration file for any installed operating systems.

NVIDIA One of the foremost manufacturers of graphics cards and chipsets.

object System component that is given a set of characteristics and can be managed by the operating system as a single entity.

object access auditing Feature of Event Viewer’s Security section that creates an entry in the Security Log when certain objects are accessed, such as a file or folder.

ohm(s) Electronic measurement of a cable’s impedance.

OpenGL One of two popular APIs used today for video cards. Originally written for UNIX systems, but now ported to Windows and Apple systems. (See also DirectX.)

optical disc/media Types of data discs (such as DVDs, CDs, Blu-ray Discs, etc.) that are read by a laser.

optical drive Drive used to read/write to optical discs, such as CDs or DVDs.

optical mouse Pointing device that uses light rather than electronic sensors to determine movement and direction the mouse is being moved.

optical resolution Resolution a scanner can achieve mechanically. Most scanners use software to enhance this ability.

optical zoom Mechanical ability of most cameras to “zoom” in as opposed to the digital ability.

option ROM Alternative way of telling the system how to talk to a piece of hardware. Option ROM stores BIOS for the card onboard a chip on the card itself.

OS (operating system) Series of programs and code that create an interface so users can interact with a system’s hardware, for example, DOS, Windows, and Linux.

OS X Current operating system on Apple Macintosh computers. Based on a UNIX core, early versions of OS X ran on Motorola-based hardware; current versions run on Intel-based hardware. Pronounced “ten” rather than “ex.”

OSI seven-layer model Architecture model based on the OSI protocol suite that defines and standardizes the flow of data between computers. The seven layers are:

Layer 1 The Physical layer Defines hardware connections and turns binary into physical pulses (electrical or light). Repeaters and hubs operate at the Physical layer.

Layer 2 The Data Link layer Identifies devices on the Physical layer. MAC addresses are part of the Data Link layer. Bridges operate at the Data Link layer.

Layer 3 The Network layer Moves packets between computers on different networks. Routers operate at the Network layer. IP and IPX operate at the Network layer.

Layer 4 The Transport layer Breaks data down into manageable chunks. TCP, UDP, SPX, and NetBEUI operate at the Transport layer.

Layer 5 The Session layer Manages connections between machines. NetBIOS and Sockets operate at the Session layer.

Layer 6 The Presentation layer Can also manage data encryption; hides the differences between various types of computer systems.

Layer 7 The Application layer Provides tools for programs to use to access the network (and the lower layers). HTTP, FTP, SMTP, and POP3 are all examples of protocols that operate at the Application layer.

overclocking To run a CPU or video processor faster than its rated speed.

P1 power connector Provides power to ATX motherboards.

P4 12V connector Provides additional 12-volt power to motherboards that support Pentium 4 and later processors.

P8 and P9 connectors Provides power to AT-style motherboards.

packet Basic component of communication