| Term | Description |
| Macro | A series of commands, keyboard or mouse actions that are recorded and performed automatically when a certain key is pressed or a certain command is entered. |
| Main board | See Motherboard. |
| Master Boot Record | See MBR. |
| Math Coprocessor | See Coprocessor. |
| MBR | Master Boot Record. When a hard drive is partitioned, the Master Boot Record is written to the first sector on the hard drive. It contains the Partition Table and other information needed by the BIOS to access the hard drive. |
| MCA Bus | Micro Channel Architecture. A very proprietary bus developed by IBM that had a bus speed of 10 MHz and could use multiple bus mastering devices. There were 16 and 32 bit versions and MCA expansion cards were configured using software (a reference disk and an option disk). |
| Meg | See Megabyte. |
| Megabyte | Abbreviated MB, a megabyte is equal to 1024 Kilobytes, or 1,048,576 bytes. A computer systems memory is measured in megabytes. |
| Megahertz | Abbreviated MHz, a system's clock speed is measured in Megahertz or millions of cycles per second. The speed of computer devices or chips associated or synchronized with the system clock will be measured in MHz. e.g.: CPUs and system Bus. |
| Memory | Refers to actual chips on the motherboard, expansion cards and devices that can hold information or data for processing. |
| Memory Address | The computer assigns numbers or addresses to physical memory locations on boot up to keep track of the information that the CPU has access to. This process is referred to as Memory Mapping. |
| Memory Cache | See Cache. |
| Memory Mapping | See Memory Address. |
| Menu Bar | When a window is open, the Menu Bar is just below the Title Bar and displays the names of an applications pull down menus that provide access to the different functions and features of that particular program. |
| Microchip | See Integrated Circuit Chip. |
| Microprocessor | See Central Processing Unit. |
| MIDI | Musical Instrument Digital Interface. This is a standard that has been developed for transferring sound created by musical instruments to digital information stored on a computer. |
| MIPS | Millions of Instructions Per Second. The approximate number of commands that can be carried out in one second. A CPU's power is sometimes measured in MIPS for comparison to another CPU. |
| MMX | An enhancement to the Pentium Processor that added instructions meant to speed up the I/O needed for sound, graphics and animation or video. |
| Modem | Contraction for Modulator/Demodulator. Modems convert analog data into digital data and vice-versa so that computers can communicate over phone lines. |
| Monitor | The most commonly used output device for displaying text and graphics from a computer. CRTs (Cathode Ray Tubes) are the most common. LCDs (Liquid Crystal Displays) are used on laptops and are available for desktop systems. |
| Motherboard | The printed circuit board in a computer that contains the CPU, Chipset, expansion slots, memory and device controllers. Sometimes called the System Board, Main Board, Planar Board or Logic Board. |
| Mouse | An input device that translates movements on a horizontal surface (the mousepad) into movements of a pointer or cursor on the monitor screen. |
| MPEG | Moving Pictures Experts Group. A standard that has been developed for compression of motion video. It keeps track of the movement from frame to frame and only replaces or stores the data that has changed. |
| MSDOS.SYS | One of the system files in the MS-DOS Operating System. A hidden file in the root directory, sometimes called the kernal for DOS. When an application needs to access a device or peripheral, this file translates the request into actions that IO.SYS can perform. |
| Multimedia | Computer presentations that can make use of video, animation, sound and pictures. |
| Multimedia Extensions | See MMX. |
| Multimeter | A Voltmeter or Ammeter that has a switch setting allowing it to measure voltage (ac or dc), resistance in ohms or continuity of a circuit. |
| Multiplier | The factor by which the bus speed is multiplied to get the CPU clock speed. |