Master-slave (technical)
Encyclopedia
Master/slave is a model of communication
where one device
or process
has unidirectional control over one or more other devices. In some systems a master is elected from a group of eligible devices, with the other devices acting in the role of slaves.
On November 2003
, the County of Los Angeles sent an e-mail to its suppliers asking them not to use these terms:
.)
There were rumors of a major push to change the way hardware manufacturers refer to these devices . It has not had much effect on most of the products being produced. The designation of hard drives as master/slave may decline in a few years, with SATA
replacing older IDE (PATA) drives. This standard allows only one drive per connection, and does not require the use of master/slave terms.
Communication
Communication is the activity of conveying meaningful information. Communication requires a sender, a message, and an intended recipient, although the receiver need not be present or aware of the sender's intent to communicate at the time of communication; thus communication can occur across vast...
where one device
Computer hardware
Personal computer hardware are component devices which are typically installed into or peripheral to a computer case to create a personal computer upon which system software is installed including a firmware interface such as a BIOS and an operating system which supports application software that...
or process
Process (computing)
In computing, a process is an instance of a computer program that is being executed. It contains the program code and its current activity. Depending on the operating system , a process may be made up of multiple threads of execution that execute instructions concurrently.A computer program is a...
has unidirectional control over one or more other devices. In some systems a master is elected from a group of eligible devices, with the other devices acting in the role of slaves.
Examples
- In database replication, the master database is regarded as the authoritative source, and the slave databases are synchronized to it.
- Peripherals connected to a busComputer busIn computer architecture, a bus is a subsystem that transfers data between components inside a computer, or between computers.Early computer buses were literally parallel electrical wires with multiple connections, but the term is now used for any physical arrangement that provides the same...
in a computer system. - Railway locomotiveLocomotiveA locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th...
s operating in multiple (for example: to pull loads too heavy for a single locomotive) can be referred to as a master/slave configuration - with the operation of all locomotives in the train slaved to the controls of the first locomotive. See - Multiple-unit train controlMultiple-unit train controlMultiple-unit train control, sometimes abbreviated to multiple-unit or MU, is a method of simultaneously controlling all the traction equipment in a train from a single location, whether it is a Multiple unit comprising a number of self-powered passenger cars or a set of locomotives.A set of...
. - DuplicationLoop bin duplicatorA loop bin duplicator is a specialized audio tape machine used in the duplication of pre-recorded audio cassettes.- Analog Loop Bin Duplicator :...
is often done with several cassette tape or compact discCompact DiscThe Compact Disc is an optical disc used to store digital data. It was originally developed to store and playback sound recordings exclusively, but later expanded to encompass data storage , write-once audio and data storage , rewritable media , Video Compact Discs , Super Video Compact Discs ,...
recorders linked together. Operating the controls on the master triggers the same commands on the slaves, so that recordingRecordingRecording is the process of capturing data or translating information to a recording format stored on some storage medium, which is often referred to as a record or, if an auditory medium, a recording....
is done in parallel. - In parallel ATA hard drive arrangements, the terms master and slave are used but neither drive has control over the other. The terms also do not indicate precedence of one drive over the other in most situations. "Master" is merely another term for device 0 and "slave" indicates device 1.
- On the MacintoshMacintoshThe Macintosh , or Mac, is a series of several lines of personal computers designed, developed, and marketed by Apple Inc. The first Macintosh was introduced by Apple's then-chairman Steve Jobs on January 24, 1984; it was the first commercially successful personal computer to feature a mouse and a...
platform, Target Disk ModeTarget Disk ModeTarget Disk Mode is a boot mode unique to Macintosh computers.When a Mac that supports Target Disk Mode is started with the 'T' key held down, its operating system does not boot...
allows a computer to operate as an external FireWire hard diskHard diskA hard disk drive is a non-volatile, random access digital magnetic data storage device. It features rotating rigid platters on a motor-driven spindle within a protective enclosure. Data is magnetically read from and written to the platter by read/write heads that float on a film of air above the...
, essentially a disk slave mode. Some older pre-FireWire Macintoshes had a similar controversial "SCSISCSISmall Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
Disk Mode".
Controversy
Sometimes the terms master and slave are deemed offensive.On November 2003
November 2003
November 2003: January – February – March – April – May – June – July – August – September – October – November – December-Events:-November 1, 2003:...
, the County of Los Angeles sent an e-mail to its suppliers asking them not to use these terms:
Many in the Information Technology field rebuff this claim of discrimination and offence as ridiculous, noting that the master/slave terminology accurately reflects what is going on inside the device and that this was not intended in any way to be a reference to slavery as it existed in the United States. (See also political correctness
Subject: IDENTIFICATION OF EQUIPMENT SOLD TO LA COUNTY
Date: Tue, 18 Nov 2003 14:21:16 -0800
From: "Los Angeles County"
The County of Los Angeles actively promotes and is committed to ensure a work environment that is free from any discriminatory influence be it actual or perceived. As such, it is the County's expectation that our manufacturers, suppliers and contractors make a concentrated effort to ensure that any equipment, supplies or services that are provided to County departments do not possess or portray an image that may be construed as offensive or defamatory in nature.
One such recent example included the manufacturer's labeling of equipment where the words "Master/Slave" appeared to identify the primary and secondary sources. Based on the cultural diversity and sensitivity of Los Angeles County, this is not an acceptable identification label.
We would request that each manufacturer, supplier and contractor review, identify and remove/change any identification or labeling of equipment or components thereof that could be interpreted as discriminatory or offensive in nature before such equipment is sold or otherwise provided to any County department.
Thank you in advance for your cooperation and assistance.
Joe Sandoval, Division Manager
Purchasing and Contract Services
Internal Services Department
County of Los Angeles
Political correctness
Political correctness is a term which denotes language, ideas, policies, and behavior seen as seeking to minimize social and institutional offense in occupational, gender, racial, cultural, sexual orientation, certain other religions, beliefs or ideologies, disability, and age-related contexts,...
.)
There were rumors of a major push to change the way hardware manufacturers refer to these devices . It has not had much effect on most of the products being produced. The designation of hard drives as master/slave may decline in a few years, with SATA
Sata
Sata is a traditional dish from the Malaysian state of Terengganu, consisting of spiced fish meat wrapped in banana leaves and cooked on a grill.It is a type of Malaysian fish cake, or otak-otak...
replacing older IDE (PATA) drives. This standard allows only one drive per connection, and does not require the use of master/slave terms.
See also
- Advanced Technology Attachment (ATA), uses master/slave configuration
- Flexible single master operationFlexible single master operationFlexible Single Master Operations , or just single master operation or operations master, is a feature of Microsoft's Active Directory...
- Bus masteringBus masteringIn computing, bus mastering is a feature supported by many bus architectures that enables a device connected to the bus to initiate transactions...
- Master clockMaster clockA master clock is a precision clock that provides timing signals to synchronize slave clocks as part of a clock network. The master clock in such installations is controlled by an accurate quartz crystal oscillator, usually referenced to an external frequency standard such as MSF, which is part of...