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 RadioShack Consumer Electronics Glossary: M

M-: see Mega- (M-).
 
m-: see Milli- (m-).
 
M3U (.m3u)
Acronym: MPEG-3 URL (Universal Resource Locator)
Audio: The file extension used by many media players for an MP3 audio file playlist. Like the RAM (.ram) file extension, M3U files contain only the information identifying to the actual location of the MP3 audio file.
 
Macro
Digital Video: The ability of a lens to focus very close (less than 8") for taking pictures of small objects at a 1:1 ratio.
Plug 'n Power: A sequence of X-10 commands
 
Magnetic Field
DIY: The force that surrounds a magnet.
 
mA
DIY, Electronics, Measurement: A unit of electrical current; one milliamp is one-thousandth (1/1000) of an ampere.
 
mAh
Batteries, Measurement: A unit of battery capacity; one milliamp-hour is one-thousandth (1/1000) of an ampere-hour.
 
Major Trading Area: see MTA.
 
Mammatocumulus
Weather: an obsolete term for cumulonimbus mammatus, it is a portion of a cumulonimbus cloud that appears as a pouch or udder on the under surface of the cloud. Although they do not cause severe weather, they often accompany storms.
 
MAN
Acronym: Metropolitan Area Network
Telephony: A network covering an area larger than a Local Area Network (LAN) and smaller than a Wide Area Network (WAN). Typically, a MAN connects two or more LAN's and may carry voice, video, image and multimedia as well as data. Compare to CAN, HAN, LAN, WAN.
 
MARS
Acronym: Military Affiliate Radio System
Communications: MARS begin in November, 1925 as the Army Amateur Radio System (AARS) in order to enlist the talents of volunteer Amateur Radio operators as a source to train soldiers to use radio equipment as well as to pursue radio research and development to improve radio equipment within the Army.

This organization existed continuously from 1925 until the United States entry into World War II, at which time radio Amateurs were denied the use of the air. AARS was not allowed to go back on the air until 1946. In 1946, the AARS was reactivated and resumed its role of training military personnel until the creation of the Military Amateur Radio System in 1948, later renamed the Military Affiliate Radio System (MARS).

MARS member stations meet periodically in scheduled networks on military frequencies outside of amateur bands. There are various types of networks and each accomplishes a specific goal. For example, administrative networks take care of the day-to-day management of the program; traffic networks exist solely to pass third-party traffic; and of course, emergency networks provide for communications needs during periods of emergency. There are also technical nets and training nets.

MARS nets operate in different modes. Although high frequency (HF) single sideband (SSB) voice is predominant, there are RATT, VHF, PACKET, PACTOR, GTOR, CLOVER and even slow scan TV nets.

 
Mare's Tail
Weather: Thin, wispy cirrus clouds composed of ice crystals that appear as veil patches or strands, often resembling a horse's tail.
 
Matrix
Metal Detectors: The total volume of ground penetrated by the transmitted electromagnetic field which may contain varying amounts and combinations of minerals, metals, salts and moisture.
 
Matrix Array
Digital Video: A CCD that can instantly capture full-color images.
 
Matrix Metering
Digital Video: A metering method which uses the entire image; however, it breaks the area down into smaller segments and uses the individual readings to calculate the best possible exposure. Matrix-metering is the most accurate of the metering systems.
 
Maxwell
Electronics, Metal Detectors, Measurement: A unit of magnetic flux. One Maxwell equals one magnetic line of force.
 
MB
Acronym: MegaByte
Computer, Data Storage: A unit of measurement equal to 1024 kilobytes or 1,048,576 bytes.
 
Mb
Acronym: Megabit
Computer, Data Transfer: A unit of measurement equal to either 1,000 kilobits / 1,000,000 bits (data transfer), or 1,024 kilobits / 1,048,576 bits (data storage).
 
mb
Acronym: millibar
Weather: The standard unit of measurement for atmospheric pressure used by the National Weather Service. One millibar is equivalent to 100 newtons per square meter. Standard surface pressure is 1,013.2 millibars.
 
Mbps
Acronym: Megabits per second
Computer, Data Transfer: A measurement of data transfer speed equal to 1,000 kilobits per second, or 1,000,000 bits per second.
 
MD
Acronym: Mini Disk
Audio: A trademarked recordable optical media by Sony, consisting of a small optical disc contained within a protective 72mm by 68mm case in order to protect the disc from scratching, bending and exposure. ATRAC (Adaptive Transform Acoustic Coding) provides a 1:5 compression ratio, allowing up to 80 minutes of 44.1 kHz audio data to recorded to a single MiniDisc. The MiniDisc playback also uses SRM (Shock Resistant Memory) technology to store up to 20 seconds (depending on the unit) of audio data so that can be played if the player is bumped and/or the reading laser head is knocked out of place.
 
Mean Temperature: see Temperature, Mean.
 
Mebi- (Mi-)
Measurement, Computers: New SI / Metric unit of binary measurement, not yet fully adopted, equal to 220 or 1, 048, 576.
 
Mega- ( M-)
Measurement: SI / Metric unit of decimal measurement, equal to 106 or 1,000,000.
Measurement, Computers: Unit of binary measurement, equal to 220 or 1, 048, 576.
 
Measurement: The metric prefix for one million (example: 1 MB is one megabyte or 1,000,000 bytes).
Computer, Data Storage: When referring to data storage (megabit, megabyte), mega- indicates 1,048,576 (or 10242).
 
Megabyte: see MB.
 
Megahertz: see MHz.
 
Megapixel: see MP.
 
Megohm
DIY, Measurement: Equals 1 million ohms.
 
Melting Point
Weather: The temperature at which a solid substance undergoes fusion, changing from a solid to a liquid state. Contrast with freezing point.
 
Memory Card
Digital Audio, Digital Video, Computers: A small card on which files can be saved. These cards are very small in size, but can hold up to 64 MB of information.
 
Memory Effect
Batteries: A term used to describe an issue with Ni-Cd batteries, characterized by the effective capacity of the battery being significantly impaired. In the original sense, this problem was caused by a cyclic memory issue. Presently, the term is also used to describe the problem of internal crystal growth, which also causes this problem.
 
Memory Stick
Digital Audio, Digital Video, Computers: A flash memory storage device developed by Sony that comes in sizes from 4 MB up to 128 MB.
 
Mercury Barometer: see Barometer, Mercury.
 
Mercury, Inches of
Weather: The name comes from the use of mercury barometers which equate the height of a column of mercury with air pressure. One inch of mercury is equivalent to 33.86 millibars or 25.40 millimeters. First devised in 1644 by evangelista torricelli (1608-1647), an italian physicist and mathematician, to explain the fundamental principles of hydromechanics. Related term: barometric pressure
 
Mesh
Computers, Networking: A network topology in which the computers are connected as illustrated below. See also Bus, Ring, Star, Tree.
Mesh Topology
 
Mesopause
Weather: The separation point in the atmosphere located between the mesophere and the thermosphere.
 
Mesosphere
Weather: The layer of the atmosphere located between the stratosphere and the ionosphere, where temperatures drop rapidly with increasing height. It extends between 31 and 50 miles (17 to 80 kilometers) above the Earth's surface.
 
Metal
Metal Detectors: Metallic substances such as iron, foil, nickel, aluminum, gold, brass, bronze, lead, copper, silver, etc.
 
Metal-film Resistor: see Resistor, Metal-film.
 
Metal-particle
Video: A technology used to create magnetic videotapes.
 
Metal-Oxide Semiconductor Field-Effect Transistor: see MOSFET.
 
Metal-oxide Resistor: see Resistor, Metal-oxide.
 
Meteorology
Weather: The study of the chemical properties, dynamic motions, and physical processes of the atmosphere.
 
Meter
Metal Detectors: A detector component that provides visual information to aid in target identification. Meters feature either an LCD or needle indicator which may display intensity of signal, target depth, target identification, type of metal, or battery condition.
Measurement: A unit of measurement equal to 39.37 inches.
 
Metering
Digital Video: The process of calculating the exposure from the existing light conditions. See Matrix Metering, Spot Metering and Center Weighted.
 
Metric Prefixes
Measurement: The metric prefixes are used to indicate a particular value for a unit. In standard use, the value is based on a base-10 (decimal) system and expressed as 10 to a given power. In computing, some of the metric terms are used to refer to amounts based on a base-2 (binary) system and expressed as 2 to a given power. In 1998, the International Electrotechnical Commission introduced new prefixes for binary values in order to eliminate confusion.
Standard Values
Prefix Abbr 10# Value
yotta-  Y-   1024 1,000,000,000,000,000,000,000,000
zetta- Z- 1021 1,000,000,000,000,000,000,000
exa- E- 1018 1,000,000,000,000,000,000
peta- P- 1015 1,000,000,000,000,000
tera- T- 1012 1,000,000,000,000
giga- G- 109 1,000,000,000
mega- M- 106 1,000,000
kilo- k- 103 1,000
hecto- h- 102 100
deka- da- 10 10
deci- d- 10-1 0.1
centi- c- 10-2 0.01
milli- m- 10-3 0.001
micro- µ- 10-6 0.000001
nano- n- 10-9 0.000000001
pico- p- 10-12 0.000000000001
femto- f- 10-15 0.000000000000001
atto- a- 10-18 0.000000000000000001
zepto- z- 10-21 0.000000000000000000001
yocto- y- 10-24 0.000000000000000000000001

Computing Values

Prefix Abbr 2# Value
Old New Old New
exa- exbi- E- Ei- 260 1,152,921,504,606,846,976
peta- pebi- P- Pi- 250 1,125,899,906,842,624
tera- tebi- T- Ti- 240 1,099,511,627,776
giga- gibi- G- Gi- 230 1,073,741,824
mega- mebi- M- Mi- 220 1,048,576
kilo- kibi- K- Ki- 210 1,024
 
Metropolitan Area Network: see MAN.
 
Metropolitan Statistical Area: see MSA.
 
MHz
Acronym: MegaHertz
Measurement: A unit of frequency equal to 1,000,000 cycles per second, 1000 kHz or 1,000,000 Hz.
 
Mi-: see Mebi- (Mi-).
 
Mic-level
Audio: An audio signal coming directly from a microphone. A mic-level signal has a very low power rating and requires a preamp to be used with line-level equipment.
 
micro- (µ-)
Measurement: SI / Metric unit of decimal measurement, equal to 10-6 or 0.000001.
 
Microampere (µA)
DIY, Measurement: Equals 1 millionth of an ampere.
 
Microbarograph
Weather: A instrument designed to continuously record a barometer's reading of very small changes in atmospheric pressure.
 
Microbrowser
Internet: A Web browser that is designed to run in the low-memory and small-screen environment of an Internet device, such as a PDA or smart telephone.
 
Microcontroller
Electronics: An IC which is designed to control a particular system. Because it is serves a specialized function, it can be made smaller and cheaper than a general-purpose controller.
 
Microfarad (µfd)
DIY, Measurement: Equals 1 millionth of a farad.
 
Microphone
Audio: An electronic device that converts sound energy into electrical energy.
 
Microphone, Boundary
Audio: A microphone that is designed to be mounted on an acoustically reflective surface. Also called Surface Microphone.
 
Microphone, Capacitor
Audio: A microphone that operates by the pressure variation on the movable plate of a capacitor causing variations in capacitance.
 
Microphone, Carbon
Audio: A microphone that operates by the pressure variation in carbon granules causing a change in resistance. Carbon microphones were commonly used in old telephone handsets. The carbon granules tended to settle and compress, reducing the microphone's clarity. Because of this, it was periodically necessary to agitate the handset (often by knocking it against the nearest hard surface) in order to loosen the granules.
 
Microphone, Electret
Audio: A microphone that uses an electret (electrical-magnet) to hold a permanent electrical charge, enabling it to function in low-voltage applications.
 
Microphone, Lavalier or Lavaliere
Audio: A small electret microphone designed to be worn (usually via a clip) rather than carried.
 
Microphone, Surface: see Microphone, Boundary.
 
Microwave
Communications, Telephony: A frequency band between 1 GHz and 30 to 40 GHz, comprised of very short wavelength radio waves.
 
Microwave Multi-point Distribution System: see MMDS.
 
Middle Clouds: see Clouds, Middle.
 
Midrange
Audio: A speaker driver designed to reproduce the middle range of frequencies.
 
Mile, Nautical 
Measurement: A unit of length used in sea and air navigation, based on the length of one minute of arc of a great circle. One unit is equal to1,852 meters (about 6,076 feet).
 
Military Affiliate Radio System: see MARS.
 
milli- (m-)
Measurement: SI / Metric unit of decimal measurement, equal to 10-3 or 0.001.
 
Milliamp: see mA.
 
Milliamp-Hours: see mAh.
 
Millibar: see mb.
 
Millihenry (mH): DIY, Measurement: Equals 1 thousandth of a henry.
 
Milliwatt (mW): DIY, Measurement: Equals 1 thousandth of a watt.
 
MIME
Acronym: Multipurpose Internet Mail Extensions
Internet: The standard format, developed and adopted by the Internet Engineering Task Force (IETF), for including non-text information in Internet mail, thus supporting the transmission of mixed-media messages across TCP/IP networks. In addition to covering binary, audio, and video data, MIME is the standard for transmitting foreign language text which cannot be represented in ASCII code.
 
MIN
Acronym: Mobile Identification Number
Telephony: A semi-fixed number assigned by the wireless carrier to a customer's telephone which can be changed if the customer transfers the telephone to another customer or moves to another city. See also ESN, IMSI, MSID, TMSI.
 
Mineralized Ground: see Ground, Mineralized.
 
MiniDisc: see MD.
 
Mist
Weather: A collection of microscopic water droplets suspended in the atmosphere. It does not reduce visibility as much as fog and is often confused with drizzle.
 
Mixer
Audio: A circuit or device that accepts two different signals and outputs a combination of those signals as per the specifications or settings for the circuit or device.
 
MMC
Acronym: MultiMedia Card
Digital Audio, Digital Video: A flash memory card used in some digital cameras, MP3 players and cellular telephones. The other major memory card type is called SmartMedia™. The two types are not interchangeable.
 
MMDS
Acronym: Microwave Multi-point Distribution System or Multipoint Multichannel Distribution Service
Telephony: A method of distributing cable television signals through microwave from a single transmission point to multiple receiving points.
 
MMS
Acronym: Multimedia Messaging Service
Telephony: MMS is the third phase of message service development, and allows full multimedia content (from text to voice to video). It requires 2.5 G and 3G networks and a full channel, rather than fitting into existing channel space as do SMS (Short Message Service), the first phase, and EMS (Enhanced Messaging Service), the second phase.
 
Mobile
Telephony: A cellular telephone.
Communications: A non-stationary (or non-base station) transceiver, such as a transceiver mounted in a vehicle, a handheld transceiver or a control station.
 
Mobile Coverage Area
Telephony, Communications: A geographical area in which two-way radio service can be expected between a base station and mobile unit.
 
Mobile-ID
Telephony: The 7-digit telephone number for an individual cellular telephone, not including the area code.
 
Mobile Identification Number: see MIN.
 
Mobile Satellite Service: see MSS.
 
Mobile Station Identifier: see MSI.
 
Mobile Telephone Switching Office: see MTSO.
 
Mode
Electronics: A user-selectable operating condition that allows for a specific function (or functions).
 
Modulation
Telephony: The process of encoding information for transmission.
 
Modulation, Analog
Telephony: The process of converting audio information into a modification of the carrier signal (corresponding to either the amplitude or frequency). See AM and FM.
 
Modulation, Digital
Telephony: The process of converting audio information into a series of digital bits and vice versa. Digital modulation offers a cleaner signal than analog modulation.
 
Module, Appliance
Plug 'n Power: Receiver part of the Plug 'n Power system that is designed to control appliances up to 500W of power. Only respond to ON/OFF command. For safety purpose these units do not respond to the "All lights ON" command.
 
Module, Lamp
Plug 'n Power: Receiver part of the Plug 'n Power system that is designed to control lamps. They do respond to the dimmer command and to "All lights ON" command. Up to 300W of incandescent lighting can be connected to these modules.
 
Moiré
Digital Video: An artifact that appears as a visible pattern where there should be no pattern, usually created when halftone screens in a color image are not registered properly.
 
Monaural: see Mono.
 
Mono
Acronym: (short for) Monophonic
Audio: Refers to single-channel sound. When mono sound is sent to multiple speakers, each speaker gets the exact same signal.
 
Morse Code
Communications: A code developed by Samuel Morse in the 1840's to allow letters to be sent as a combination of short and long electrical signals. The original code (also called American Morse Code) was replaced in England and Europe by a modified code called Continental or International Morse Code, which is now the standard morse code. Morse code is still used in some fields of communication.
 
MOSFET
Acronym: Metal-Oxide Semiconductor Field-Effect Transistor
Electronics: Also known as an Insulated Gate Field Effect Transistor. A field effect transistor in which the insulating layer between the gate electrode and the channel is a metal oxide layer. See FET and J-FET.
 
MOSFET, Enhancement-mode
Electronics: A field effect transistor in which there are no charge carriers in the channel when the gate source voltage is zero.
 
Motion Sensor
Plug 'n Power:  
MOV
Acronym: MOVie
Digital Video: A motion video file format created by Apple® and used with the QuickTime® player.
 
MP
Acronym: Megapixel
Digital Video: Literally, one million pixels. A megapixel digital camera has an image resolution of 1280 x 960 pixels or greater. The most common digital cameras are rated at 1.3 megapixel, 2.11 megapixel and 3.34 megapixel.
 
MP3
Acronym: MPEG-1 Layer 3
Digital Audio: A digital audio compression algorithm that achieves a compression factor of about 12:1 while preserving sound quality.
 
MP3 Player
Audio: A software program that allows you to listen to MP3 audio files.
 
MP3Pro
Audio: An audio codec developed by Thomson Multimedia in order to provide the MP3-equivalent audio quality in smaller file sizes.
 
MP3 Utility
Audio: Any of a series of software tools that allow you to manipulate MP3 audio files.
 
MPEG
Acronym: Moving Pictures Experts Group
Digital Video:
1) A working group under ISO / IEC (both associations within SMPTE) which sets the standards for audio and video compression methods.
2) A set of standards for compressing digital movie and sound files.
3) A motion movie file which uses the MPEG standards.
 
MPEG-1 Layer 3: see MP3.
 
MSA
Acronym: Metropolitan Statistical Area
Telephony: A geographic cellular coverage region (CGSA) which encompasses a densely populated area. See RSA.
 
MSAudio
Acronym: MicroSoft Audio
Audio: An audio compression codec created and used by Microsoft®.
 
MSID
Acronym: Mobile Station Identifier
Telephony: The identification code for a mobile cellular telephone -- either a Mobile Identification Number (MIN) or an International Mobile Subscriber Identity (IMSI).
 
MSS
Acronym: Mobile Satellite Service
Telephony: A communications transmission service provided by satellites.
 
MTA
Acronym: Major Trading Area
Telephony: A service area used by the FCC for PCS coverage. MTA's are centered on a major city and generally cover an area the size of a state. See also BTA.
 
MTSO
Acronym: Mobile Telephone Switching Office
Telephony: The central computer that connects a wireless telephone call to the public telephone network and controls the entire system's operations, including call monitoring, billing, and hand-offs.
 
Multimeter
DIY: A piece of electrical test equipment capable of measuring multiple parameters, such as voltage, current, resistance, capacitance, inductance.
 
Multimeter, Analog
DIY: A piece of test equipment that measures volts, ohms, amps, and other electrical characteristics, and displays the reading by moving a needle over a fixed scale.
 
Multimeter, Digital
DIY: A piece of test equipment that measures volts, ohms, amps, and other electrical characteristics, and displays the reading on a digital display.
 
Multimedia Card: see MMC.
 
Multi-megapixel
Digital Video: An image or image sensor with over two million pixels.
 
Multipoint Multichannel Distribution Service: see MMDS.
 
Multipurpose Internet Mail Extensions: see MIME.
 
Multi Spot Focusing
Digital Video: An autofocus system using several different portions of the image to determine the proper focus.
 
Multiple Exposure
Digital Video: An image made up of two or more superimposed images.
 
Multi-switch
Satellite: A device which allows you to have up to four satellite receivers connected to a single satellite antenna, with each receiver capable of independent tuning. This device requires that you have a Dual LNB satellite antenna, and can also be used as a combiner if a broadcast antenna is connected. If a TV antenna is connected, you would need to use a Splitter/Combiner at each receiver to split the output into separate TV antenna and DTH signals.

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