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"M" Networking Definitions & Concepts...

Mac Boot Process .. to .. Multiuser

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M, or Mega:

A prefix denoting 106, or a million; for example, Mbps, or megabits per second.

Mac Boot Process: (OS 1.0 -- 9.2.2)

The Macintosh has a complicated process for starting up the machine. Knowing more about the process will allow users to troubleshoot problems they have booting in the future and understand better how the Macintosh works.

Here is the process:

  1. The Macintosh is powered on and performs a test of RAM and other motherboard components. Motherboard video is initialized,
  2. The Mac ROM initializes all NuBus or PCI cards, causing drivers to be loaded from these cards. Video card drivers are loaded first, then drivers from other cards,
  3. If Command-Option-C is pressed, the Mac will attempt to boot off its CD-ROM Drive. (On Macintoshes introduced from 1995),
  4. If Command-Option-TAB is pressed, the Mac will attempt to boot off its floppy drive,
  5. It checks for bootable floppies in the floppy drive,
  6. The Mac looks at its parameter RAM (PRAM) to see if a device has been chosen in the Startup Device control panel. Once drivers for all block devices that can be found are loaded, the value stored in PRAM is compared with those of each drive in the drive queue. When the correct drive is found, it is mounted and the chosen folder/directory (if any) is sought,
  7. The Mac then looks at the Startup Device's partition map and loads a SCSI driver for the Startup Device from its Apple_Driver partition,
  8. If no Startup Device is set or if the Starup Device is missing, the Mac scans the first SCSI bus it encounters and looks for bootable drives from the highest SCSI ID to the lowest ID,
  9. The SCSI driver is called to mount volumes of type Apple_HFS found in the drive's partition map and to read boot blocks in from the first volume,
  10. All other SCSI devices have their drivers loaded and are mounted,
  11. Compatibility of the current System file and the computer is checked.
  12. The SCSI driver is called to read the System file in,
  13. Startup screens are displayed if present,
  14. Welcome to Macintosh is displayed,
  15. If the Mac requires a System Enabler, the Enabler is read in.
  16. MacsBug, if present in the System folder/directory, is loaded.
  17. The Mac loads all System Extensions, Chooser Extensions (print drivers, etc.), and Control Panels that have Extensions embedded in them,
  18. The Macintosh launches any Startup applications (in startup folder/directory in the System Folder/directory) and loads the Finder to bring up the Desktop.

NOTE: For information on PC boot process, see "PC Boot Process".

MACH (Micro-kernel ArChitecture), Carnegie-Mellon Microkernel:

A kernel is the core component of most operating systems. It is the portion that manages memory, resources, files, peripherals, and system security. The kernel typically runs processes and provides interprocess communication among them. The Mach operating system was developed at Carnegie-Mellon University. It has a client-server architecture consisting of a relatively small kernel called a microkernel. The microkernel architecture is designed to handle only the most critical functions of the operating system, as listed here:

  • Interrupts
  • Messaging
  • Thread scheduling
  • Virtual Memory

Compare the Mach microkernel to a person who owns and manages a business. While the manager could attempt to run the entire business alone, the growth of the business will eventually depend on hiring others to handle some of the business operations. By delegating part of the workload to others and reducing his or her workload, the manager can be more efficient. Additional people are added as necessary to grow with the business.

In a similar manner, the Mach operating system uses a modular design in which additional functions are attached to the microkernel as necessary. These other functions include a file management module, a network support module, a module that runs a graphical user interface, and other modules. The modules are layered on top of the Mach microkernel.

The modules communicate using interprocess communication mechanisms. Remote procedure calls (RPCs) provide communication over a network with processes running on other systems. The Mach kernel is specifically designed for multiprocessing and improves system throughput on multiprocessor systems. Mach also supports external memory managers for applications such as transaction processing systems that must have their own control over memory.

A layered architecture lets the microkernel host a number of diverse operating systems such as UNIX System V, HP-UX, or an AIX version of UNIX, as well as DOS or OS/2 on multiple platforms such as the Motorola PowerPC RISC processor and Intel processors. Mach is the core of the Open Software Foundation's (OSF's) OSF/1 Microkernel operating system. It is also the core of IBM's new PowerPC operating system called Workplace OS. The IBM microkernel is small in size (about 40K) and handles basic tasks listed earlier.

Microkernel operating systems such as Mach give users choices as to the interfaces and features of their operating system. They fit in well with the changing computer market in which users choose a computer platform based on needs, not on a processor or operating system. Mach provides a way to run similar environments on a variety of different processors. The microkernel provides an interface between the user's choice of platforms and operating systems.

The modular approach lets users add only the functionality they need to an operating system. In older operating systems, built-in functions took up disk space and memory and went unused by some users. Microkernel architecture simplifies expansion of the operating system and makes upgrades and bug fixes easier since only modules are upgraded, not the entire operating system. In addition, it's possible to upgrade or change out modules while the core operating system runs. This is a great benefit in the server environment, where a downed server not only becomes inaccessible to users, but resets various tracking systems and statistical measures that rely on the amount of time the server is up and running.

Also see, IBM Operating Systems; Microkernel; OSF/1, Open Software Foundation; Remote Procedure Call; Windows NT Microsoft; and Workplace OS

Mach Ten by Tenon Intersystems:

Is a complete UNIX system that runs as a Macintosh application with the native Macintosh Operating System (MacOS). Mach Ten provides an advanced software development environment that takes advantage of Mach/UNIX virtual memory and protection.

Mach Ten provides a full suite of Internet services, distributed file system services, and remote printer spooling. These services are available not only to UNIX applications, but also to Macintosh applications. Mach Ten also supports a sophisticated set of UNIX software development tools as well as X Window software that lets you develop and access X applications.

Mach Ten is based on the University of California, Berkeley UNIX built on a Carnegie Mellon Mach kernel. The Mach kernel replaces many of the Berkeley UNIX internals and provides a number of new features not available in traditional UNIX systems. Mach Ten both refines and extends the capabilities of the native Macintosh Operating System by providing a multitasking UNIX environment that coexists with the MacOS cooperative sharing execution environment. With Mach Ten, Macintosh applications, UNIX applications, and Mach applications run simultaneously. Mach Ten represents the confluence of the best features of the Macintosh and the systematic power and elegance of UNIX and Mach.

Also see, Mach; UNIX; and X Windows

Machine Language Programming

Machine language describes the numerical codes corresponding to the instruction set that are directly recognized by the CPU (Central Processing Unit); because it corresponds to the instruction set, machine language is tied to a particular CPU. A printout of a program in machine language is a string of numbers (a very long string of 0s and 1s, even for a short program). The numbers will be written in hexadecimal for the simple reason that anyone trying to write, much less read, page after page of ones and zeros would quickly go crazy. There is very little benefit to working in machine language over assembly language. Machine Language Programming is part of the computer hierarchy associated with programming languages and machine language is what other programming languages create.


Macintosh is the shared name for a family of graphics-based computers from Apple Computer. Until very recently, these computers were built around the Motorola 680x0 family of micro-processors (for example, the 68030 or 68040).

The rather large Macintosh family consists of serveral classes of computers, with high- and low- end models in most classes.

Models in the classic series look similar to the original Macintosh (68000), released in 1984. Examples include the Classic and Classic II, as well as the LC (for low-cost color) and LC II. For both monochrome and color versions, the II versions are higher-end models than the others, but neither is very high-end when compared with other classes in the family.

Mac OS X and FreeBSD:

Mac OS X is a revolutionalry operating system in many ways. While it contains many technologies that are available in other operating systems, it brings the power and reliability of UNIX to the desktop. In fact, Mac OS X is the best-selling desktop UNIX system ever, even though many users never see its UNIX foundation. This in itself is commendable; Apple has managed to put such a pretty face on top of this foundation that users don't need to know what's under the hood. Also, it's the first UNIX-based system that can run both command-line tools and a wide range of consumer and business productivity, graphics, and game software.

Mac OS X is based on FreeBSD, one of many UNIX operating systems. It is one of two main branches of UNIX; BSD is the Berkely Software Distrbution (so named because it was developed at the University of California -- Berkeley); the other is the System V brach. Both of these operating systems are different from Linux, which is actually a kernel wrapped in one of many distributions, though there are numerous simularities between UNIX and Linux systems. In fact, Linux users with strong command-line experience will find Mac OS X easy to adapt to. Some of the key system functions are radically different, but the majority of the commands are similar, and they'll find the same shells they are used to using on their favorite Linux distributions.

Mac OS X does a good job of hiding its UNIX-based foundations. Many of the essential system files are not normally visible in the Finder, so users who don't need to know about them will never see them. But with the command line and Terminal -- the application you use to interact with the command-line -- one can see all these files, edit them, and configure the Mac in ways one con't from the Aqua interface.


The most popular way to run TCP/IP protocols on a Mac is with Apple's own MacTCP. This driver is frequently packaged with many of the TCP/IP-based programs, such as TELNET, X Windows, and NFS, currently available to provide additional services to a Mac user. MacTCP conforms to various Internet standards and provides the basic IP-related protocols (TCP, UDP, and IP). MacTCP allows you to run both TCP/IP and AppleTalk processes at the same time, for example, simultaneously running a TELNET session and printing to a Printer on LocalTalk. With the introduction of MacTCP 1.1, which is compatible with System 7.0, you can use alternate Link Access Protocols, such as token ring, PPP, and SLIP; formerly only Ethernet was supported. The current version for MacTCP is 2.0.6.

Another Apple driver is Open Transport. This is a new network extension that removes the limit of 64 Mac TCP/IP connections running at once.


A mainframe is a large system with one or more central processors. Multiple processors share the processing load or provide backup processing should one of the units fail. The systems can provide gigabytes of online data storage and archive storage. Mainframes were the primary computers in the 1960's and early 1970's and were manufactured by IBM, DEC, Burroughs, Control Data, Honeywell, Univac, and others. A distinguishing feature is that they provide centralized processing for terminals or desktop computers that emulate terminals. All the processing is performed by the mainframe system.

IBM and others still manufacture mainframes, but the role of the mainframe is changing. IBM has developed strategies for integrating mainframes into enterprise computing environments. These systems can provide intensive computing power for client-server applications or serve as a data repository as outlined in IBM's Information Warehouse strategy. IBM recognizes that organizations have a diversity of systems, and it now supports multiple communication protocols and open systems as defined in its Networking Blueprint. For example, Transmission Control Protocol/Internet Protocol (TCP/IP) and Open Systems Interconnection (OSI) protocols are now supported on IBM networks, along with Advanced Peer-to-Peer Networking (APPN) and Advanced Program-to-Program Communications (APPC).

In the 1970's and 1980's, Digital Equipment established itself as a minicomputer vendor by providing efficient, cost-effective systems for departmental use. Today, most desktop computers have the memory, storage, and processing power of yesterday's minicomputers. While DEC has strengthened its line, many vendors of superservers (desktop PCs with multiple processors and vast amounts of memory) are encroaching on its turf. The new DEC Alpha AXP processors are proving to be strong contenders, however. The processors are built into single- and multiprocessor systems that run Windows NT and other industry-standard operating systems.

It is said that microcomputer systems linked by networks and running client-server applications will supplant the mainframe, but this has not yet occurred. In fact, while desktop computer systems are approaching mainframes in processing power, they still can't compare to mainframes in overall features. A mainframe can handle, in one location, huge amounts of input/output (I/O), online transaction processing, security, data integrity, availability, and management functions. In addition, there is a large installed base of mainframe applications and databases that do not currently require replacement. In fact, IBM sees an increased demand for new applications that support the Networking Blueprint and Information Warehouse strategy.

Other contenders for this market include UNIX-based Reduced Instruction Set Computer (RISC) systems. Over the last few years, these systems have gained tremendous processing power. Enhancements to the operating system and applications have also helped the systems gain ground. In addition, UNIX has supported the popular TCP/IP communication protocols, which are used on the internetworking due to efficient routing methods.

IBM Mainframe Systems

IBM's original line of mainframe computers, called the S/360, where introduced in 1964. These were largely batch processing systems in which a group of transactions were processed together, rather than one at a time. In 1970, the line was upgraded to the series S/370, and time-sharing was the major paradigm in which many users could access the computer through terminals. In the 1980's and 1990's, the series S/390 represents IBM's strategy for interactive computing.

The current processors that conform to this heritage are the IBM Enterprise System/9000 (ES/9000) series. The systems come in a variety of sizes, from water-cooled systems with up to six processors to air-cooled systems with up to four processors. Input/output channels are managed with Reduced Instruction Set Computer (RISC) processors and external devices are attached with high-speed fiber optic links.

The ES/9000 systems are part of IBM's enterprise system strategy that supports open environment and multiple protocols. IBM is already installing many of these systems as network servers and information warehouse systems.

Also see, Alpha AXP, DEC; Client-Server Computing; DEC; Distributed Computing; IBM; IBM Mainframe Environment; IBM Networking Blueprint; Information Warehouse; Reduced Instruction Set Computer (RISC); and UNIX


A humorous term applied to packets that turn up unexpectedly on the wrong network, usually because of incorrect and/or errors in the routing tables.


Millions of Bits Per Second -- A measure of the rate of data transmission.

Memory Pool:

In Novell's NetWare, a memory pool of a finite supply of memeory, not necessarily contiguous. NetWare 4.x uses only a single memory pool, whose resources are allocated for whatever functions request them. NetWare version 3.x defines several memory pools, including a short-term and a file cache pool.

Message Switching:

In message switching, a message makes its way from sender to receiver by being passed through intermediate nodes. Each node may store the entire message, and it will forward it to the next node when the opportunity arises.

Under certain types of connections, different parts of the message may take different routes to the destination during transmission. By using message switching and a store-and-forward method, a network operating system can make the most effective use of the available bandwidth.

Metadata: (Database)

Data about data. Usually the data stored in a data dictionary. This is data that describes the data stored in the database. Data that describe the properties or characteristics of other database data.

Metal Oxide Varistor (MOV):(Electronics)

An electrical component in a line conditioner or surge protector. MOVs help clip high-energy spikes from an incoming supply, by shorting the excess energy to ground. Compare MOV with capacitor and inductor.


Reference from microcode, microcode is similar to a microprogram, which is a highly-specialized computer program that allows one computer microarchitecture to emulate another, usually more-complex architecture. The microprogram is usually very small compared to ordinary software, hence its name. It is also very carefully designed and optimized for the fastest possible execution.

It is also known as the lowest-level of instructions that directly control a microprocessor. A single machine-language instruction typically translates into several microcode instructions.

A code, representing the instructions of an instruction set, that is implemented in a part of storage that is not program-addressable.

Directions that define machine language instructions. Each machine instruction is a complete microprogram. Microcode directly controls how the hardware functions. Microcode runs in a fast memory called a control store.

Microcomputer workstations vs. dumb/intelligent terminals:

The reason microcomputer workstations are superior to dumb/intelligent terminals is because, microcomputer workstations have compute power that is very close to and in some cases can exceed the compute power of mainframe computers. Terminals dump and/or intelligent in general depend on the host system for computational power and/or data exchange. Dump/Intelligent Terminals depend on hosts for their application usage. Microcomputers can do the majority of their computations locally (i.e., they have "smart" circuitry and a central processing unit), with occasional transmission over the network, where the dumb and/or intelligent terminals communicate constantly over the network sending and receiving data from a mainframe or a microcomputer workstation. However, intelligent terminals do have local compute power to some degree. That is, they have local memory, and can have auxiliary storage.

Basically dumb terminals are video terminals that do not participate in control or processing tasks. They do not contain storage systems, internal memory, or microprocessor chips. When a character is typed on one of these terminals, it is transmitted immediately to the host system. This forces the host or central system to create buffers for this type of terminal so the message can be assembled before acting on it.

Intelligent terminal are able to participate in the processing of data. These terminal contain internal memory and are capable of being programmed. Many internal terminals also contain auxiliary storage units and fast central processing units. Most of today's intelligent terminal are microcomputers and specialized microcomputer workstations. In general, intelligent terminals will not have a "software operating system", there OS is usually simple and is contained in either EPROM, or masked ROM.

However, microcomputers are an integral part of any communication networks.


A kernel provides the core functions of an operating system. A microkernel is a stripped down version of a kernel that is designed to provide more portability in less memory space, and to provide a modular design that lets users install a variety of interfaces such as UNIX, DOS, Windows, Workplace OS, and Workplace UNIX. New operating systems from IBM, Microsoft, Open Software Foundation (OSF), and UNIX System Laboratories (USL) take advantage of this approach. Two notable microkernel operating systems are listed here:

  • Mach From Carnegie-Mellon University
  • Nucleus From Chorus Systems (Beaverton, Oregon), which is headquartered in France

As mentioned, a microkernel is a stripped down version of a kernel in which the layer of system services normally integrated with the kernel are separated and become optional modules that are added as required. This provides for better scalability and more efficient application development. With a microkernel design, upgrading a system is a simple matter of replacing the old module with the new module. You don't need to replace the entire operating system.

We can use a business analogy to explain the modular concept of the microkernel. Consider an overworked business manager. By delegating duties to other people, the manager can apply his or her skills to the efficent operation of the business, and concentrate on other tasks, such as starting a new branch of the business. New people are hired to support the growing business. The manager coordinates these activities, but lets each person do the job she or he was hired to do. Likewise, a microkernel operating system runs a few core tasks and manages the activities of installable modules. In this way, the microkernel is extremely efficient at what it does and is more portable, meaning that it can be designed to run on a variety of processors.

A microkernel-based operating system is layered and has the following features:

  • A microkernel provides a "generic" set of services such as process scheduling, interprocess communications, memory management, and device I/O handling. All other services such as file management and network support interface onto this microkernel. In contrast, a kernel is integrated and much larger.
  • A microkernel is more scalable and simplifies application development. Users run only the services they need, which can help reduce disk space and memory requirements.
  • Vendors can easily port the microkernel to other processor platforms, then add modular components on top to fit the requirements of those platforms (that is, file servers, engineering applications, and so on).

The microkernel interfaces with hardware components and provides in interface for installable modules. Processes interact by passing messages and run as "threads" within the microkernel. Threads provide a way to divide a single task into multiple sub-tasks, which can then execute on separate processors in a multiprocessor system.

Important microkernel operating systems are listed here:

  • Windows NT This operating system is designed around a Microsoft-designed microkernel that closely follows the Mach design. If provides thread scheduling, interrupt and exception management, multiprocessor synchronization, and system recovery (after a power failure). It is never paged out of memory and its execution is never pre-empted by another process.
  • OSF/1 MK The latest version of the Open System Foundation's OSF/1 UNIX operating system uses a microkernel approach. It implements the Mach kernel and provides virtual memory management, interprocess communication, and device driver managament.
  • UNIX SVR4 UNIX Systems Laboratories, Inc. released a microkernel version of UNIX SVR4 (System V release 4). It implements the Nucleus microkernel. It provides all the features of a microkernel discussed above; however, drivers are not managed in the microkernel.
  • WorkPlace OS IBM's microkernel is based on the Mach microkernel. The microkernel runs on the Motorola PowerPC processor, which is a direct competitor to the Intel 80486 and Pentium processors. Users of Workplace OS can choose from a variety of interfaces that run on top of the operating system, such as DOS, OS/2, Windows, UNIX. The IBM microkernel is small in size (about 40K) and handles basic tasks such as memory management, thread management, interrupt management, and messaging.

Microkernel operating systems such as Mach and Nucleus give users choices as to the interfaces and features of their operating system. They fit in well with the changing computer market in which a variety of processors and operating systems are available. Developers also benefit. They can easily port their products from one system to another, making more applications available for end users. The modularity of the design also ensures that a rich set of optional servivces is available.

Also see, IBM Operating Systems; Mach, Carnegie-Mellon Microkernel; OSF/1, Open Software Foundation; Remote Procedure Call; UNIX; Windows NT, Microsoft; and Workplace OS


Modulation describes a range of techniques for encoding information on a carrier signal, typically a sine-wave signal. A device that performs modulation is known as a modulator.

To modulate is to imprint information -- voice, video, data, whatever; analog or digital -- onto the spine of a carrier signal, so that it can get from one place to another. Maybe from the studio to the uplink, or from the uplink to the satellite, or from the headend to the home.

A carrier signal is an electromagnetic wave, which is a form of energy -- just as heat, light and sound are forms of energy. Electromagnetic waves are invisible, and ubiquitous. One of their more interesting scientific properties is their ability to propagate through space, or over a conductor (such as a cable), essentially at the speed of light. Like most other forms of energy, the strength of the electromagnetic wave dissipates in a known and predictable manner.

An example of modulation is: Amplitude modulatiob (AM); AM is a method used to modulate a signal, typically using radio. In the case of an analog signal to be sent, the amplitude of the radio wave is modulated to be directly proportional to the value of the analog signal at the time. This should be compared to frequency modulation (FM), which modulates the frequency rather than the amplitude.

Amplitude modulation typically produces a modulated output signal that has twice the bandwidth of the modulating signal, with a significant power component at the original carrier frequency.

Monte Carlo:

A simulation technique using a pseudo-random number generator to develop multiple independent trials simulating a range and probability distribution of results.


The main circuit board in a computer or printer. This board will hold the CPU (central processing unit) and may include a math coprocessor, various other controller chips, and RAM chips. In its role as a backplane, the motherboard provides slots for expansion.


A transmission method in which one source node communicates with one or more destination nodes with a single transmission. However, in contrast to a broadcast, which is sent to all connected nodes, a multicast message is transmitted only to some of the possible recipients.

Stated another way, in packet-based networks, these packets are addressed to a predefined group of nodes on a network, but not necessarily all of the nodes. Multicast is an efficient method of broadcasting packets only to those nodes that are interested in the contents.

Ref. Unicast, and Broadcast.

Multi-homed Host:

In the Internet environment, a single machine connected to multiple data links, which may be on different networks. A multihomed host is simply a host with two or more network connections within the internetwork: it could be a Macintosh with both a LocalTalk connection and an Ethernet connection or a Unix workstation with an Ethernet connection and a SLIP connection. It can also be considered as or thought of as a host with network interfaces on more than one network; such a host will have an IP (Internet Protocol) address for each network interface.


In fiber optics, a class of fibers with a core thick enough for light to make several paths (known as modes) through the core. This is in contrast to a single mode fiber, whose core is thin enough that light can take only a single path through the core.

Multiple Access Schemes:

Multiple access schemes are "the ability of a large number of earth stations to simultaneously interconnect their respective voice, data, teletype, facsimile, and television links through a satellite". FDMA (Frequency Division Multiple Access), TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access) are the three basic multiple access schemes. In FDMA, all users share the satellite at the same time, but each transmits in its own unique frequency band. This is most commonly employed with analog modulation, where signals are present all the time. In TDMA, the users transmit in turn in their own unique time slots. While transmitting, each occupant has exclusive use of one or more transponders. "The intermittent nature of TDMA transmission makes it particularly attractive for digital modulation." In CMDA, many earth stations simultaneously transmit orthogonally coded spread-spectrum signals that occupy the same frequency band. Decoding ("despreading") systems receive the combined transmissions from many stations and recover one of them. See the diagram below.

As the diagram above shows; with Multiple-access techniques. "Here each "user" corresponds to a one-way communication link between two stations. In frequency division (FDMA), the available bandwidth B is divided among the users and all can transmit simultaneously. In time division (TDMA), only one user transmits at any time and that user can use the entire bandwidth, so the instantaneous data rate is proportional to B. In code division (CDMA) schemes, users can transmit simultaneously and also share the frequency allocation. For the frequency-hopping scheme illustrated, each user transmits with a particular pseudo-random frequency pattern. Tc is normally on the order of a bit time. Such schemes are useful for mobile applications; synchronization among users is not required."


Multiplexing technology that allows the transmission of multiple signals over a single medium. Multiplexers allow the replacement of multiple low-speed transmission lines with a single high-speed transmission line. The typical configuration includes a multiplexer attached to multiple low-speed lines, a communication line (typically four-wire carrier circuit), and a multiplexer at another site that is also connected to low-speed lines. The remote site contains terminals, microcomputers, modems, and printers attached to a multiplexer. The host site has a multiplexer, FEP, and host CPU. The operation of the multiplexers, frequently called MUX's, and are transparent to the sending and receiving computers or terminals. The multiplexer does not interrupt the normal flow of data. Multiplexers allow for a significant reduction of the overall cost of connecting remote sites, since the quantity of lines required to connect the sites is decreased.

Multiplexing techniques can be divided into frequency division multiplexing (FDM), see frequency division multiplexing, time division multiplexing (TDM), see time division multiplexing, and statistical time division multiplexing (STDM), see statistical time division multiplexing.

Multiplexers can be used in a variety of configurations and combinations. Cascading is a typical configuration used to extend circuits to remote entry points when there are two or more data entry areas. The number of ports that a multiplexer can accommodate varies. Commonly there are 4,8,16,32,64 ports. The price of a multiplexer will vary with the number of ports in it, and its level of sophistication.

The Types of Multiplexer are;
  • Inverse Multiplexer, see Inverse multiplexer
  • T-1 Multiplexer, see T-1 multiplexer
  • Multiport Multiplexer, see Multiport multiplexer
  • Fiber Optic Multiplexer, see Fiber Optic multiplexer
Multiport Multiplexer:

A multiport multiplexer combines modem and time division multiplexing (TDM, see time division multiplexing) equipment into a single device. The line entering the modem can be of varying transmission speeds. The multiport multiplexer then combines the data and transmits it over a high-speed link to another receiving multiplexer.

Multipurpose Internet Mail Extensions (MIME):

MIME is a mail handling standard developed by the IETF (Internet Engineering Task Force) to provide support for multimedia and multipart messages. MIME makes it possible to encode and transmit sound, video, and formatted data in a single message, and also to receive and handle (read, see, or hear) the message.


A thread is an executable object, which belongs to a single process or program. Each thread comes with its own stacks, registers, and instruction counter.

Multithreading is a special form of multitasking in which all the tasks come from the same program. In multithreading, multiple processes from a single program execute, seemingly at the same time. This concurrency is only apparent because, as with multitasking, the processor is actually switching its attention very rapidly among all the threads.


Refers to an environment or operating system that supports more than one user at a time. UNIX is an example of a multiuser operating systems; DOS, MacOS, and OS/2 are considered single user systems.

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