What is the master/slave model?

Master/slave is an architectural concept in information technology that describes how resources are controlled and distributed. Within this model, a master device or process has control over how and when subordinate devices and processes use resources. This model is used, for example, to generate piconets in Bluetooth.

When is the master/slave model used?

The master/slave model can be implemented when several devices, processes or applications depend on the same resources. This is, for instance, the case when transmitting data via a data bus. The master/slave model regulates requests and ensures that communication between the signals takes place without any interference or modification from other participants. This guarantees that all processes are executed correctly.


The term “master/slave” is extremely problematic given its reference to slavery. Alternative terminology is often used, including the following: “primary/secondary”, “primary/replica” and “principal/agent”.

What are some common scenarios that the master/slave model is used for?

The master/slave model is used to do the following:

  • Regulate and coordinate bus systems for information exchange: The master coordinates and controls secondary devices and ensures that the data bus receives and processes information correctly.
  • Organize resources within a computer network: The master releases the resources available in the network according to a certain logic. This ensures that all participants perform their tasks.
  • Create a piconet of terminals using Bluetooth: The master/slave model is used to create piconets. This is a [personal area network], which is a specific type of network that connects to end devices using Bluetooth.
  • Control access to a host system: A host computer provides resources within a computer network. The master regulates the participants’ access.

How does the master/slave model work?

In the master/slave model, communication is one-sided. The master can contact the slave, but it is not possible for the slave to communicate with the master. Therefore, resources are always controlled unidirectionally.

The master device or process grants the slave device or process the rights it needs. This may include access or communication rights. The slave follows the master’s requests, while the master can act as it chooses.

What are the characteristics of master/slave?

In the master/slave model, the master device or process is in control. Slave devices and processes are always passive and must wait for the master’s permission to use resources. Due to its position, the master is granted a larger range of functions and can control a large number of secondary devices and processes. The master can address the slaves with an address or a physical line. In certain systems, it is possible to define the master when initializing a system of equal stations.

What are the advantages and disadvantages of the master/slave model?

The master/slave model is a well-known concept for controlling and regulating shared resources. The main advantage is that complete access control puts the master at the center of system planning. This simplifies the process of resource sharing and also means that no unauthorized information exchange can take place. The main disadvantage of this model is the unidirectional communication. Since slaves are not able to communicate directly with the master, polling is used to regularly check the status of hardware or software. This method, however, is considered inefficient.

What are alternatives to the master/slave model?

The master/slave model is not the only architecture model for resource control and allocation. The client-server model is a well-known alternative. In this model, servers offer services that clients use. This is the most commonly used architecture model on the internet. For example, sending emails using SMTP, IMAP or POP, sending HTTP requests to a web server, and transferring data to a server using File Transfer Protocol (FTP) are all carried out using the client-server model.

The peer-to-peer model is another alternative. The peer program represents the server and client at the same time. Unlike the master/slave model, the peers have equal rights and perform both server and client tasks. Peer-to-peer architecture is used primarily for file-sharing services or grid computing.

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