Glossary

Macroblock
The four 8 x 8 blocks of luminance data and the corresponding 8 x 8 blocks of chrominance data coming from a 16 x 16 section of a picture's luminance component. The number of chrominance blocks is two for 4:2:0 chroma format, four for 4:2:2 chroma format, or eight for 4:4:4 chroma format. The term "macroblock" is sometimes used to refer to pel data and sometimes to the coded representation of the pel values and other data elements defined in the macroblock header. The usage should be clear from the context.

Main Memory
Refers to physical memory that is internal to the computer. The word main is used to distinguish it from external mass storage devices such as disk drives. Another term for main memory is RAM.

Master
An original audio tape, videotape or film; used for broadcast or to make copies.

MFM
Abbreviation of Modified frequency Modulation, an encoding scheme used by PC floppy disk drives and older hard drives. A competing scheme, known as RLL (run length limited), produces faster data access speeds and can increase a disk's storage capacity by up to 50 percent. RLL is used on most newer hard drives.

MIP-mapping
Multiple textures of increasing size are used to represent one texture. When a polygon needs to use the texture as a texture map, the texture whose size most closely matches the size of the polygon that is to be rendered is used. This reduces rendering artifacts such as "sparkling" and "moiré" patterns as well as blockiness.

MNP
Abbreviation of Microcom Networking Protocol, a communications protocol developed by Microcom, Inc., that is used by many high-speed modems. MNP supports several different classes of communication, each higher class providing additional features. Modems can support one or more classes. Class 4 provides error detection and automatically varies the transmission speed based on the quality of the line. Class 5 provides data compression. Class 6 attempts to detect the highest transmission speed of the modem at the other end of the connect and transmit at that speed.

The most common levels of MNP support are Class 4 and Class 5, frequently called MNP-4 and MNP-5. Using the data compression techniques provided by MNP-5, devices can double normal transmission speeds.

Because MNP is usually built into the modem hardware, it affects all data transmission. In contrast, software protocols, such as Xmodem and Kermit, affect only file transfer operations.

MODEM
Acronym for modulator-demodulator. A modem is a device or program that enables a computer to transmit data over telephone lines.
Computer information is stored digitally, whereas information transmitted over telephone lines is transmitted in the form of analog waves.
A modem converts between these two forms.

Fortunately, there is one standard interface for connecting external modems to computers called RS-232. Consequently, any external modem can be attached to any computer that has an RS-232 port, which almost all personal computers have. There are also modems that come as an expansion board that you can insert into a vacant expansion slot. These are sometimes called onboard or internal modems.

While the modem interfaces are standardized, a number of different protocols for formatting data to be transmitted over telephone lines exist. Some, like CCITT V.34, are official standards, while others have been developed by private companies. Most modems have built-in support for the more common protocols -- at slow data transmission speeds at least, most modems can communicate with each other. At high transmission speeds, however, the protocols are less standardized.

Aside from the transmission protocols that they support, the following characteristics distinguish one modem from another:

bps : How fast the modem can transmit and receive data. At slow rates, modems are measured in terms of baud rates. The slowest rate is 300 baud (about 25 cps). At higher speeds, modems are measured in terms of bits per second (bps). The fastest modems run at 57,600 bps, although they can achieve even higher data transfer rates by compressing the data. Obviously, the faster the transmission rate, the faster you can send and receive data. Note, however, that you cannot receive data any faster than it is being sent. If, for example, the device sending data to your computer is sending it at 2,400 bps, you must receive it at 2,400 bps. It does not always pay, therefore, to have a very fast modem. In addition, some telephone lines are unable to transmit data reliably at very high rates.
voice/data: Many modems support a switch to change between voice and data modes. In data mode, the modem acts like a regular modem. In voice mode, the modem acts like a regular telephone. Modems that support a voice/data switch have a built-in loudspeaker and microphone for voice communication.

auto-answer : An auto-answer modem enables your computer to receive calls in your absence. This is only necessary if you are offering some type of computer service that people can call in to use.

data compression : Some modems perform data compression, which enables them to send data at faster rates. However, the modem at the receiving end must be able to decompress the data using the same compression technique.

flash memory : Some modems come with flash memory rather than conventional ROM, which means that the communications protocols can be easily updated if necessary.

Fax capability: Most modern modems are fax modems, which means that they can send and receive faxes.

To get the most out of a modem, you should have a communications software package, a program that simplifies the task of transferring data.

Communications Protocols

Protocol	Maximum Transmission Rate	Duplex Mode
Bell 103	300 bps	Full
CCITT V.21	300 bps	Full
Bell 212A	1,200 bps	Full
ITU V.22	1,200 bps	Half
ITU V.22bis	2,400 bps	Full
ITU V.29	9,600 bps	Half
ITU V.32	9,600 bps	Full
ITU V.32bis	14,400 bps	Full
ITU V.34	36,600 bps	Full
ITU V.90	56,000 bps	Full

Motion compensation
The use of motion vectors to improve the efficiency of predicting pel values. The motion vectors provide offsets into past and/or future reference pictures containing previously decoded pel values that are used to form the prediction error signal.

Motion estimation
The process of estimating motion vectors during the encoding process.

Motion vector
A two-dimensional vector used for motion compensation that provides an offset from the coordinate position in the current picture to the coordinates in a reference picture.

MPC
A trademarked abbreviation for Multimedia Personal Computer. The original MPC specification was developed by Tandy Corporation and Microsoft as the minimum platform capable of running multimedia software. In the Summer of 1995, the MPC Marketing Council introduced an upgraded MPC 3 standard.

The MPC 1 Specification defines the following minimum standard requirements: a 386SX or 486 CPU; 2 MB RAM; 30 MB hard disk; VGA video display; 8-bit digital audio subsystem; CD-ROM drive; and systems software compatible with the applications programming interfaces (APIs) of Microsoft Windows Version 3.1 or higher.

The MPC 2 Specification defines the following minimum standard requirements: 25 MHz 486SX with 4 MB RAM; 160 MB hard disk; 16-bit sound card; 65,536 color video display; double-speed CD-ROM drive; and systems software compatible with the applications programming interfaces (APIs) of Microsoft Windows Version 3.1 or higher.

The MPC 3 Specification defines the following minimum standard requirements: 75 MHz Pentium with 8 MB RAM; 540 MB hard disk; 16-bit sound card; 65,536 color video display; quad speed CD-ROM drive; OM-1 complaint MPEG-1 video, and systems software compatible with the applications programming interfaces (APIs) of Microsoft Windows Version 3.1 and DOS 6.0 or higher.

MPEG (Motion Picture Experts Group)
A working committee which, under the auspices of the International Standards Organization, has defined standards for the digital compression and decompression of motion video/audio for use in computer systems. These standards consist of MPEG-1 and MPEG-1.

The MPEG-1 standard delivers decompression data at 1.2 to 1.5 MB per second, allowing CD players to play full-motion color movies at 30 frames per second. MPEG-1 compresses at about a 50:1 ratio before image degradation occurs, but compression ratios as high as 200:1 are attainable. Building on the MPEG-1 standard is MPEG-2, which extends to the higher data rates (2-15 Mbps) needed for signals delivered from remote sources (such as broadcast, cable, or satellite). MPEG-2 is designed to support a range of picture aspect ratios, including 4:3 and 16:9.

Multimedia-Ready
Multimedia-ready disc drives are designed for graphics, audio and video applications. They have a capacity of at least 800 Mbytes and an average sustained data-transfer rate of at least 3 Mbytes per second. Data-transfer interruptions that can cause jerky video are eliminated by the use of embedded-servo or specially implemented dedicated-servo technology.