MAC (Media Access Control)
A protocol from the Institute of Electrical and Electronics Engineers, defining the methods used to gain access to the physical layer of a LAN — that is, Layer 1 of the Open Systems Interconnection (OSI) model (see OSI).

MAC (message authentication code)
An encrypted code used to verify the integrity of a block of transmitted data.

MAC (moves, adds and changes)
General term for the routine work performed on computer equipment in an enterprise, including installations, relocations and upgrades (sometimes referred to as "IMAC," for "installations, moves, adds and changes").

MACRS (Modified Accelerated Cost Recovery System)
The tax depreciation system introduced by the U.S. Tax Reform Act of 1986. It became effective for all servers placed in service after year-end 1986.

MAD (mass access device)
A non-PC device that provides Internet access. Examples include Web-enabled set-top boxes, mobile phones and personal digital assistants.

MAD (mergers, acquisitions and divestitures)
A general term for corporate consolidation and divestiture activity.

Magic Quadrant
A two-dimensional graphical framework developed by Gartner that places a particular set of vendors from a specific technology industry sector into a strategic matrix. Gartner analysts use multiple objective and subjective criteria to evaluate individual vendors, presented on two axes:

mainframe
A large-capacity computer system with processing power that is significantly superior to PCs or midrange computers. Traditionally, mainframes have been associated with centralized, rather than distributed, computing environments. Skilled technicians are required to program and maintain mainframes, although client/server technology has made mainframes easier to operate from the user's and programmer's perspectives. They are generally used by large organizations to handle data processing for enterprisewide administrative tasks like payroll or accounts payable.

mainstream notebook
A computer system that meets all the criteria for a notebook PC but is designed to be the best compromise between all-inclusive functionality and light weight. Mainstream notebooks weigh between 4.5 and 6 pounds with the weight-saver and battery modules. Mainstream notebooks often have a single bay for the inclusion of a peripheral, such as a CD-ROM. See notebook.

MAN (metropolitan-area network)
A type of network that evolved from local-area network (LAN) designs, but is optimized for longer distances (more than 50 kilometers), greater speeds (more than 100 megabits per second) and diverse forms of information (such as voice, data, image and video).

managed object
A data processing or data communications resource that may be managed through the use of an Open Systems Interconnection (OSI) management protocol. The resource itself need not be an OSI resource. A managed object may be a piece of equipment, a software component, an abstract collection of information or a combination of all three.

managed services
Externally provided operations and management capabilities delivered over a networked infrastructure, using a monthly subscription model or recurring charge. Managed services can be provided for networks, security, databases, servers, storage and applications. See MSSP (managed security service provider) and network managed services.

management consulting
Strategic consulting focused on high-level corporate or business unit strategy (for example, deciding what businesses to participate in or whether to make an acquisition), or on operational improvement (for example, improving customer service or determining the most effective type of retail delivery system).

MAPI (Messaging Application Programming Interface)
The Microsoft-developed programming interface specification that enables an application to send and receive mail over an e-mail messaging system, such as Microsoft Exchange. It was designed to separate the mail engine from the mail client.

MAPICS (Manufacturing Accounting and Production Information Control System)
A manufacturing enterprise resource planning (ERP) product, originally introduced by IBM as software for the AS/400 and earlier System/36 and System/38 systems. MAPICS was later taken over by Marcam, and separated into an independent company in 1997.

mapping
The transcription of functions into terms that make them equivalent on two different systems. In network operations, it is the logical association of one set of values, such as addresses, on one network with quantities or values of another set, such as devices, on a second network (such as name-address mapping).

master
A computer or device that has total control over another computer or device (the "slave").

materials management
A manufacturing term used to describe the grouping of management functions related to the complete cycle of material flow, from the purchase and internal control of production materials, to the planning and control of work in progress, to the warehousing, shipping and distribution of the finished product.

MB (megabyte)
Approximately million bytes (1,048,576, to be precise). This is the common unit used to specify the size of computer files, storage capacity or random-access memory (RAM). The relationship of the size of a file or accumulation of files to the size of the RAM and storage space is critical, because it determines the ability of a computing device to process a file.

Mb (megabit)
Approximately one million bits of computer data (1,048,576, to be precise).

MBE (molecular beam epitaxy)
A semiconductor manufacturing technology.

Mbps (megabits per second)
A measure of data transmission speed.

MBR (mean bit rate)
The number of bits transmitted per time unit averaged over the period of the session.

MBS (maximum burst size)
In asynchronous transfer mode (ATM), the number of cells a source is allowed to send at the peak cell rate. See ATM.

m-business (mobile business)
Gartner uses this term to describe the new business models and opportunities enabled by the extensive deployment of mobile and wireless technologies and devices — such as Bluetooth, Wireless Application Protocol (WAP), Universal Mobile Telecommunications System (UMTS), general packet radio service (GPRS), smartphones and e-purses — in support of the inherent mobility of most people's work styles and lifestyles. M-business is a key factor driving the emergence of the Supranet (see separate entry). The value proposition of m-business is that the user can benefit from information or services at any time or in any place. To successfully prepare for m-business, business and IT managers must address three key challenges:

MCIF (marketing customer information file)
A customer information file (CIF) system that supports marketing, rather than operational, activities. An MCIF typically has some or all of the characteristics of a data warehouse, but is designed specifically to support the marketing function. See CIF and data warehouse.

MCM (multichip module)
A type of integrated-circuit packaging configuration.

MCNS (Multimedia Cable Network System)
The cable industry joint venture that created the Data-Over-Cable Service Interface Specification (DOCSIS). MCNS was formed by Comcast Cable Communications, Cox Communications, Time Warner Cable and Tele-Communications (which was later acquired by AT&T). See DOCSIS.

m-commerce (mobile commerce)
A category of commerce that includes any purchase transaction completed using a wireless device, such as a cellular phone, PC or personal digital assistant. M-commerce includes paying for a subscription to get content "pushed" to a mobile device, purchasing a product via a mobile device or using such a device to obtain a service for which a fee is charged. Purchases that are researched or arranged via a wireless device, but completed and settled by other means, are classified as mobile-enabled transactions.

MCR (minimum cell rate)
An asynchronous transfer mode (ATM) parameter used to determine the minimum number of cells permitted in a specific time period. See ATM.

MD5 (Message Digest Algorithm 5)
An algorithm used in ensuring message integrity.

MDF (Message Development Framework)
A detailed formal methodology for Health Level Seven (HL7) message development, adopted by the HL7 organization in 1997.

Merced
Intel's code name for its first 64-bit (IA-64) processor.

MEMS (microelectromechanical systems)
Microsystems that are composed of both mechanical and electronic parts. Most MEMS systems today are based on silicon, are manufactured using integrated circuit (IC) batch-processing techniques, and follow the deposit-and-etch methods found in IC fabrication. While MEMS devices such as sensors and actuators have been around some time, it is only in the past few years that MEMS design and fabrication have begun to venture out of mostly automotive and military applications and into the telecommunications and computer markets.

MES (manufacturing execution system)
A computerized system that formalizes production methods and procedures within the manufacturing environment, providing online tools to execute work orders. The term is generally used to encompasses any manufacturing system not already classified in the enterprise resource planning (ERP) or open control system (OCS) categories. In the broadest definition, MESs include computerized maintenance management systems (CMMSs), laboratory information management systems (LIMSs), shop floor controls, statistical process systems, quality control systems, and specialized applications such as batch reporting and control. See ERP, OCS, CMMS and LIMS.

mesh network
A net-like network configuration where at least two paths exist to all stations.

message authentication
A function in which a network-attached device determines if the received message arrived from its stated source and in unaltered form. The actual message need not be encrypted, but its authentication code must be.

message broker
A logical hub that copies and resends messages to one or more destinations. As a value-adding third party between information sources and information consumers, it can complement a service-oriented architecture (SOA). Like an SOA, a broker is a design abstraction that may be implemented using component software for some or all of the connections. The interface from a message broker to the application may use an object request broker (ORB) or object transaction monitor (OTM); a request to the message broker may be implemented as a series of method calls to participating components. See SOA, ORB and OTM.

message format
Rules for the placement of portions of a message, such as the heading, address, text, end-of-message indication and error-detecting bits. See message.

message passing
Services performing a simple, one-way transfer operation between two programs. Like other one-way messaging models, message passing generally leaves the sending program unblocked. Also, as with all forms of messaging, message passing is usually connectionless, which means that the sending application does not have to explicitly establish and manage a connection with the message's intended recipient. Although message passing is not inherently a two-way communication model, two-way communication can be accomplished by sending the response in a separate message.

message queuing
A model similar to that of message passing, but with one additional feature: Message queuing is asynchronous in a manner similar to a traditional postal system — that is, the recipient need not be available when the message is sent. Message queuing stores messages at an intermediate node on the network in a queue and then forwards the messages to the intended targets. See message passing.

message warehouse
A message broker service that temporarily stores messages to be analyzed or retransmitted at a later time. See message broker.

metadata
Information about data, including attributes such as description, length and location. For example, the fact that a field in a given database is called "client number" and is five characters long is metadata. By comparison, a given instance of the client number "123456" in that database field is just "data."

metadirectory
A directory that acts as a superset of all other directories. Metadirectories have evolved from stand-alone products to services that enable a given directory to synchronize and exchange information with other data repositories.

metatag
As a noun or verb, this term refers to the tagging of documents with metadata (such as keywords, dates, categories or creators) to enhance search efficiency. See metadata.

metalanguage
A language used to describe a language. A metalanguage defines a language's constructs, such as character sets, syntax and valid sequences.

metric
A standard of measurement.

MFLOPS (million floating-point operations per second)
A performance measurement unit for floating-point-intensive applications.

MFP (multifunction product)
A network-attached document production device that combines two or more of the copy, print, scan and fax functions.

MGCP (Media Gateway Control Protocol)
An Internet Engineering Task Force signaling protocol allowing a bridge between classic telephone networks and Internet Protocol (IP) infrastructures; a voice over IP (VoIP) standard. See VoIP.

MHz (megahertz)
A unit equal to 1 million hertz (1 million cycles per second).

MIB (management information base)
A Simple Network Management Protocol (SNMP) flat-file, nonrelational database that describes devices being monitored. Network management platforms monitor nodes by reading the value of the managed resources in the MIB. Management platforms can effect changes in managed resources by altering MIB values — for example, by establishing thresholds beyond which alerts are created. See SNMP.

MIC (memory in cassette)
A media feature with which Sony has differentiated its Advanced Intelligent Tape (AIT) drive. MIC is a 16-kilobit electrically erasable programmable read-only memory (EEPROM) chip that indexes file locations, thus enabling faster access to data, and stores metadata about the media, allowing enterprises to track media life cycles in the physical cartridge. See AIT and EEPROM.

MICR (magnetic-ink character recognition)
Machine recognition and digitization of magnetically charged characters printed on paper (typically bank drafts and deposit slips).

microbrowser
A browser that differs from a typical browser in its storage size and scaled-down functionality. Microbrowsers perform client-side functions that render Web content to a particular device. They share responsibility for this task with back-end servers by controlling the presentation layer at the server level, the client level, or as a hybrid of the two.

microcode
The microinstructions, especially of a microprocessor, that govern the details of operation. Microcoded functions can improve performance but add a layer of complexity. For example, microcode errors appear to software as being hardware failures.

microfilm
A high-resolution film used to record images reduced in size from the original. Also known as microfiche.

microprocessor
A central processing unit (CPU) on a single chip, also known as a microprocessing unit. Desktop and portable computers typically contain one microprocessor, while more powerful computers often make use of multiple microprocessors. See CPU.

microwave
The portion of the electromagnetic spectrum above about 760 megahertz. Many communication technologies employ microwave frequencies, including line-of-sight, open-air microwave transmission facilities and, increasingly, satellite communications.

middleware
The software "glue" that helps programs and databases (which may be on different computers) work together. Its most basic function is to enable communication between different pieces of software.

midrange
A general term for the category of computers or servers that fall into the range above minicomputers (such as PCs) and entry-level servers on the low end, and below mainframe systems on the high end. Midrange systems may or may not run proprietary operating systems. By Gartner Dataquest's market definition, midrange servers have a minimum average selling price (ASP) of $10,000 or more and may reach an ASP of more than $100,000.

MIMD (multiple instruction, multiple data)
A design for parallel computers characterized by the simultaneous execution of many different instruction streams (programs), each of which handles different data.

MIME (Multipurpose Internet Messaging Extensions)
A set of functions that enables the transport of attachments and nonstandard text via Simple Message Transport Protocol (SMTP). MIME covers most of the features of X.400 while minimizing the transformation of addresses and attachments. See SMTP and X.400.

minicomputer
A computing device that is typically more powerful than a PC, but less powerful than a mainframe, and is therefore often referred to as "midrange." A minicomputer can support multiple users. See midrange.

Minitel
An online information system that debuted in France in the 1970s. Minitel was the world's first electronic information system for public use — a forerunner of today's Internet.

MIPS (million instructions per second)
An approximate measure of a computer's raw processing power. MIPS figures can be misleading because measurement techniques often differ, and different computers may require different sets of instructions to perform the same activity.

MIPS RISC
A reduced instruction set computer (RISC) processor architecture designed and licensed by MIPS Computer Systems (now part of Silicon Graphics). Used by a number of midrange suppliers, it was the basis for the Advanced RISC Computing definitions endorsed by the now-defunct Advanced Computing Environment consortium.

mirroring
Replicating data on different computers or devices to provide backup or improved performance. In a storage sense, "mirroring" refers to duplicating data on multiple disk storage devices to provide backup in the event of a system failure. In an Internet sense, "mirroring" refers to replicating the contents of a Web site at another site to minimize load on the main server, or to speed up connectivity in a specific geographic region.

MIS (management information systems)
This was once the predominant name for the central data-processing organization in an enterprise. Today, information systems (IS) is the more commonly used term. See IS.

mission-critical
A term used to describe applications that are critical to the survival of an enterprise. Mission-critical services require a combination of several factors, such as availability, reliability, serviceability and performance. Each of these must be weighted in importance to fit the particular mission to be supported.

MMDS (multichannel multipoint distribution service)
A fixed wireless technology that operates between 2.5 gigahertz (GHz) and 2.7 GHz. MMDS is used for broadcasting, personal communications and interactive media services in metropolitan areas.

MMI (man-machine interface)
Another term for an end-user interface.

MMS (Multimedia Messaging Service)
A mobile-messaging standard jointly defined by the 3G Partnership Project (see 3GPP) and the Wireless Application Protocol Forum (see WAP Forum). MMS provides a broad set of features that cannot be delivered through traditional wireless-messaging standards, such as the ability to send and receive messages containing rich multimedia content, and to send messages to both mobile phone numbers and e-mail addresses. Unlike Enhanced Messaging Service (see EMS), MMS does not draw on established messaging technology such as Short Message Service (see SMS). Instead, it requires new infrastructure to be deployed by the network operators, and new functionality in mobile terminals.

MNS (managed network services)
The vendor delivery of primarily operational support for a network environment in which the hardware assets, financial obligations and personnel remain on the books of the customer.

MO (magneto-optical)
A type of storage technology that uses magnetization produced by a focused light beam. MO disks resemble write-once disks with one major difference — the same track on a disk can be written over 1 million times.

Mobile IP
A standard — proposed by a working group within the Internet Engineering Task Force — that defines a packet-forwarding mechanism for mobile and remote hosts, so that remote users can connect to their networks over the Internet. It can work with Dynamic Host Configuration Protocol (DHCP). See DHCP.

mobile middleware
Middleware that enables the implementation of distributed applications connecting mobile and enterprise applications over wireless networks (see middleware). Many 100-percent wireless products created to fill in the missing functionality are now merging into prevalent application integration and middleware products, such as application servers. As vendors of traditional middleware try to offer comprehensive wireless solutions, they will either build them internally, or acquire or partner with specialized wireless vendors.

mobile portal
A Web site with a wide range of content, services and links designed for mobile devices. A mobile portal (also known as a "wireless portal") acts as a value-added middleman by selecting the content sources and assembling them in a simple-to-navigate (and customizable) interface for presentation to the end-user's mobile device.

mobile terminal
Any mobile device that can connect to a wireless network. Data-centric examples include wireless personal digital assistants (PDAs). Voice-centric examples include basic and enhanced mobile phones. (See PDA, basic phone, enhanced phone, smartphone and Web phone.)

modal dispersion
Signal distortion in an optical-fiber cable that causes the light to spread so much that the signal cannot be received.

modem (modulator-demodulator)
A conversion device that allows a computer to transmit information over analog communication lines (for example, traditional phone lines) by converting information that is digitally stored on the computer into transmission signals. The transmitting-end modem modulates digital signals received locally from a computer or terminal and sends analog signals over the line. The receiving-end modem demodulates the incoming signal, converting it back to its original (i.e., digital) format and passes it to the destination business machine.

modulation
The application of information onto a carrier signal by varying one or more of the signal's basic characteristics (frequency, amplitude or phase), or the process of converting a signal from its original format into one that that can be transmitted over a given carrier signal. Specific types include the following (see separate entries):

modulator
A device that converts a voice or data signal into a form that can be transmitted.

MOM (message-oriented middleware)
A model that programs the delivery of a message or a reply that must be deferred. MOM differs from other forms of program-to-program middleware, such as remote procedure calls (RPCs) and conversational services, in that MOM communication is connectionless — the sending and receiving programs do not interact directly. A program sends the message to the MOM, which then takes responsibility for delivering it to the proper receivers. See middleware and RPC.

monitor
Computer hardware used for displaying digital output.

Moore's Law
The idea that computing power doubles every 18 months, originally conceived by Intel co-founder Gordon Moore in 1965.

Mosaic
A user-friendly Internet front end developed at the University of Illinois; the prototype for most of today's Web browsers.

MOSPF (Multicast OSPF)
A protocol that extends Open Shortest Path First (OSPF) routing to enable Internet Protocol (IP) multicasts. Advanced primarily by Nortel Networks (originally via Bay Networks), MOSPF is an advanced protocol, but it is not natively supported on any Cisco Systems platform, and thus has never met with widespread acceptance. See IP and OSPF.

motherboard
A computer's primary printed circuit board (PCB), also known as the system board. See PCB.

Motif
A graphical user interface (GUI) specified by the Open Software Foundation (now the Open Group) and built on the Massachusetts Institute of Technology's X-Windows. See GUI and X-Windows.

MP3 (MPEG Layer 3)
An open Moving Picture Experts Group (MPEG) standard for digital audio compression. It offers significant compression while retaining good to excellent audio quality. Files compressed with MP3 can be transmitted over the Internet using a low-bandwidth connection. Standard, uncompressed audio — as recorded on a compact disc (CD) — requires about 740 megabytes for a 74-minute CD. MP3 can compress this data size by approximately 12 to 1. The size and quality of MP3 files varies depending on the sampling rate used in conversion. A rate of 128 kilobits per second (Kbps) results in an MP3 file that is approximately one megabyte per minute of music, with near-CD-quality audio. Dropping the sampling rate to 80 Kbps or 64 Kbps results in smaller files with audio quality that is reasonable, but inferior to that of a CD.

m-payment (mobile payment)
A payment initiated or completed through a wireless device. As a point of entry into retail payments, many carriers are targeting the underdeveloped market for micropayments (payments of less than $10) for digital content and physical goods.

MPEG (Moving Picture Experts Group)
A digital video standard for compression of full-motion images. The compression ratios achieved with MPEG encoding make it an ideal standard for delivery of digital video data. MPEG-1 deals with mono and stereo sound coding, at sampling frequencies commonly used for high-quality audio. MPEG-2 contains an extension to lower sampling frequencies, providing better sound quality at the low bit rates, and an extension for multichannel sound. MPEG-3 and MPEG-4, with further improvements, are under development. Both MPEG-1 and MPEG-2 have a three-layer structure. Each layer represents a family of coding algorithms. Layer 3 deals with sound encoding, and can't be used by itself to encode audio files. In this form, it is known as MPEG Layer 3 (MP3). See MP3.

MPLS (Multiprotocol Label Switching)
A protocol that helps support quality of service in Internet Protocol (IP) networks. A router labels packets to assign different levels of service based on different priority levels. This helps ease congestion for high-priority network traffic, such as that needed for mission-critical applications. See IP.

MPP (massively parallel processing)
A high-performance computing (HPC) architecture that uses dozens, hundreds or even thousands of processors operating in parallel. Specifically, Gartner Dataquest defines MPP systems as systems configured with 32 or more processors. See HPC and supercomputer.

MRI (magnetic resonance imaging)
The use of nuclear magnetic resonance technology to create cross-section images of the human body for medical diagnostic purposes.

MRO (maintenance, repair and operations)
The activities associated with the operation and repair of any facility, equipment or asset, and the material purchased to support these activities.

MRP (material requirements planning)
An early category of manufacturing business software, which focused only on planning manufacturing materials and inventories, and did not integrate planning for other resources, such as people and machine capacity.

MRP II (manufacturing resource planning)
A method for planning all the resources of a manufacturing company, including business planning, production planning, master production scheduling, material and capacity requirements, and execution systems. MRP II systems were a precursor to enterprise resource planning (ERP) and ERP II systems. See ERP and ERP II.

ms (millisecond)
A unit of time equal to one one-thousandth of a second.

MSCS (Microsoft Cluster Service)
A Microsoft feature that provides server failover for enterprises seeking high-availability solutions. MSCS was introduced as part of Windows NT 4.0 Enterprise Edition and is now bundled, in various levels of functionality, into most of the Windows server operating systems. Originally called "Microsoft Cluster Server," the name was changed to "Cluster Service" with the introduction of the Windows 2000 Advanced Server and Datacenter Server editions. See cluster.

MSDE (Microsoft Data Engine)
A desktop database engine that works as an extension of SQL Server 7.0 to store data for offline application components. In the latest, SQL Server 2000-based edition, MSDE 2000, Microsoft changed the expanded form of the acronym to " Microsoft SQL Server 2000 Desktop Engine." See MSDE 2000.

MSDE 2000 (Microsoft SQL Server 2000 Desktop Engine)
A version of SQL Server 2000 that enables users to use a local computer as a data source for an SQL Server database, and uses the enhanced features in Microsoft Access 2002.

MSDN (Microsoft Developer Network)
A community of practice for developers created by Microsoft. MSDN offers Web-based and offline services to programmers who write applications using Microsoft technologies.

MS-DOS (Microsoft Disk Operating System)
The version of Disk Operating System (DOS) sold by Microsoft for early IBM and compatible personal computers (PCs). Until the introduction of Windows, MS-DOS was the most popular PC operating system. Versions sold by IBM were known as "PC-DOS." See DOS, PC-DOS and Windows.

MSE (midsize enterprise)
Another name for a midsize business. See SMBs (small and midsize businesses).

M-Services (Mobile Services)
An initiative to provide a framework of specifications for new Global System for Mobile Communications (GSM) mobile handsets. The M-Services initiative was launched in 2001 by the GSM Association, which believes that one barrier to mass-market adoption of Internet-enabled mobile services is the lack of a single set of comprehensive specifications for mobile-terminal manufacturers to adhere to. See GSM.

MSIL (Microsoft Intermediate Language)
An intermediate, CPU-independent language (also known as IL, or Intermediate Language) into which source code is compiled in Microsoft's Common Language Infrastructure (CLI), part of its .NET platform. The Common Language Runtime (CLR) includes a compiler for converting MSIL to native code. See CLI, CLR and .NET.

MSMQ (Microsoft Message Queuing)
A message-queuing middleware product (or, more accurately, an operating-system service) that provides store-and-forward connectivity between two application programs. See message queuing.

MSN (Microsoft Network)
Microsoft's online service, launched in 1995. It offers Internet access, Web content and related services,

MSO (management services organization)
A service organization of an integrated delivery system (IDS) or hospital. An MSO provides management services for multiple affiliated physician practices and clinics. See IDS.

MSP (management service provider)
Also known as "managed-service providers," MSPs deliver network, application, system and e-management services across a network to multiple enterprises, using a "pay as you go" pricing model. A "pure play" MSP focuses on management services as its core offering. In addition, the MSP market includes offerings from other providers — including application service providers (ASPs), Web hosting companies and network service providers (NSPs) — that supplement their traditional offerings with management services. See ASP and NSP.

MSSP (managed security service provider)
A company that provides outsourced monitoring and management of security devices and systems. Common services include managed firewall, intrusion detection, virtual private network, vulnerability scanning and antivirus services. MSSPs use high-availability security operation centers (either from their own facilities or from other data center providers) to provide 24x7 services designed to reduce the number of operational security personnel an enterprise needs to hire, train and retain to maintain an acceptable security posture.

MSU (million service units)
Performance/capacity ratings assigned to IBM S/390 and zSeries systems, and compatible mainframes from Hitachi and Amdahl. MSUs are generally comparable to millions of instructions per second (MIPS), with one MSU equaling between 5.5 and 6.0 MIPS. Historically, all S/390-class software, both from the hardware vendors and independent software vendors, is priced based on server capacity, as determined by performance data. Pricing schemes such as Parallel Sysplex License Charge are based on MSUs.

MTA (message transfer agent)
The store-and-forward portion of an e-mail system. See store and forward.

MTBF (mean time between failures)
The estimated or actual average time period between failures in a computer component or system; also known as MTTF (mean time to failure).

MTP (Message Transfer Part)
An Integrated Services Digital Network (ISDN) term for the mechanism that ensures reliable functional signal message transmission. It corresponds to the first three layers of the Open Systems Interconnection (OSI) reference model. See ISDN and OSI.

MTS (Microsoft Transaction Server)
An NT-based transactional-middleware product introduced by Microsoft in 1997.

MTTR (mean time to repair)
An estimated or actual average time required to perform repairs on a computer component or system.

mu-chip
A tiny radio frequency identification (RFID) tag, or "e-tag," introduced in 2001 by Hitachi through its in-house venture company, Mu-Solutions. It measures 0.4 square millimeters and is thin enough (60 microns) to be embedded in paper. It can store 128 bytes, which must be written at the time of manufacturing and cannot be changed. See RFID and e-tag.

multicast
A signal transmitted to only a subset of potential destinations (as opposed to a broadcast), typically over an Internet Protocol (IP) network. See IP multicast.

multidimensional database
A database constructed specifically to support the analysis of quantitative data along multiple dimensions.

multidrop
A communications arrangement where multiple devices share a common transmission channel, though only one may transmit at a time. See multipoint.

multimedia
Applications and technologies that manipulate multiple media types, such as text, data, images, sound and full-motion-video. Given the use of multiple formats, multimedia is capable of delivering a stronger and more engaging message than standard text. Multimedia files are typically larger than text-based information and are therefore usually stored on CD-ROMs. Games and educational software commonly use multimedia.

multimode
The ability of communications media, devices or equipment to support or transmit multiple transmission modes (i.e., frequencies).

multiplexing
The division of a transmission facility into two or more channels. This can be accomplished either by splitting the frequency band transmitted by the channel into narrower bands, as in frequency division multiplexing (FDM), or by allotting one common channel to several different information channels at different times, as in time division multiplexing (TDM). See FDM and TDM.

multipoint
Pertaining or referring to a communications line to which three or more stations are connected. It implies that the line physically extends from one station to another until all are connected. See point to point.

multiprocessor
A computer that incorporates multiple processors with access to common storage.

multiprogramming
A computer system operation whereby a number of independent jobs are processed together. Rather than allow each job to run to completion in turn, the computer switches between them so as to improve the use of the system hardware components.

multisourced environment
The environment that increasingly characterizes the delivery of IT and business process services in large enterprises — one in which services are provided by a mix of internal employees and functions, and external resources such as contract employees and outsourcing firms.

multisourcing
A practice (also known as selective outsourcing) in which separate outsourcing contracts are established for selected IT functions or business processes using a best-of-breed, tactical approach and competitive deals. This is the most commonly used approach for IT sourcing.

multitasking
Two or more program segments running in a computer at the same time.

multithreading
Concurrent processing of more than one thread of software code in parallel.

multiuser
The capability of a computer or system to be operated by more than one user simultaneously.

MULTOS (Multi-Application Operating System)
A smart-card operating system originally created by Mondex, and now overseen by a consortium of 13 smart card companies.

MUX (multiplexer)
A device that combines inputs from two or more terminals, computer ports or other multiplexers, and transmits the combined data stream over a single high-speed channel. At the receiving end, the high-speed channel is "demultiplexed," either by another multiplexer or by software.

MVNO (mobile virtual network operator)
A company that provides mobile network services through a contract with a mobile network operator. At the low end of the MVNO range is the company that offers mobile-telephony services through an agreement with a mobile-telephony spectrum owner, with the new entrant controlling the branding, marketing and tariff structure of the offering to customers. At the higher end is the most widely accepted definition of an MVNO: a company with its own network code, issuing its own subscriber identity module cards and controlling elements of network infrastructure, such as the home location register and mobile switching center.

MVS (Multiple Virtual Storage)
IBM's flagship mainframe operating system. Eventually superseded by OS/390 and, later, z/OS.

MVS/370
A version of MVS limited to 24-bit addressing and lacking the dynamic channel subsystem. It was dropped from support in the early 1990s.

MVS/ESA (Multiple Virtual Storage/Enterprise Systems Architecture)
A version of MVS introduced by IBM in 1988, capable of addressing up to 16 terabytes of data.