Bus Mastering

Definition of Bus Mastering

Bus mastering is a feature in computer systems that allows certain components or devices to directly communicate with each other over a shared bus, without having to pass through the CPU for data transfer. This capability reduces the workload of the CPU, while enhancing overall system performance. Bus mastering is commonly used by devices like network adapters, graphics cards, and hard disk controllers.


The phonetics of the keyword “Bus Mastering” are:Bus: /bʌs/Mastering: /ˈmæstərɪŋ/

Key Takeaways

  1. Bus mastering enables high-speed data transfers as it allows devices to directly communicate with each other over the bus without CPU intervention, thus reducing CPU load.
  2. It is a feature of advanced bus systems like PCI and PCIe, where the bus master coordinates data transfers to ensure seamless communication between multiple peripheral devices.
  3. Bus mastering can improve overall system performance, but requires appropriate support from the operating system to manage contention and priority of bus masters, to prevent issues such as data collisions and bus conflicts.

Importance of Bus Mastering

Bus mastering is an essential term in the technology realm, primarily due to its role in improving the efficiency, speed, and overall performance of computer systems.

It refers to a feature that enables certain components or devices within a computer to directly communicate with each other without needing to go through the central processing unit (CPU) for every transaction.

By allowing designated peripheral devices such as graphics cards or I/O controllers to access and manage the system bus autonomously, bus mastering not only helps in reducing bottlenecks and resource contention but also allows the CPU to focus on other critical tasks, ultimately leading to the optimized functioning of a computer system.


Bus mastering is a key function in modern computer systems, as it streamlines the communication between various components and efficiently manages data transfers. The primary purpose of bus mastering is to offload data handling responsibilities from the system’s central processing unit (CPU) to peripheral devices, consequently freeing up the CPU to concentrate on executing various other tasks.

Peripheral devices that possess this capability, such as graphics cards, network interfaces, and disk controllers, are referred to as bus masters. With bus mastering in place, these devices can effectively communicate with each other and manage the flow of information within the system, without necessitating continuous intervention from the CPU.

The implementation of bus mastering positively impacts a computer system’s overall performance, allowing it to run multiple processes simultaneously without compromising speed or efficiency. The integration of direct memory access (DMA) plays a crucial role in achieving this, as it enables bus masters to directly access the system’s memory and transport data without involving the CPU.

By facilitating faster and more streamlined data transfers within the system, bus mastering reduces the load on the CPU and contributes to a more efficient and balanced use of resources. This results in an optimized performance, particularly in complex and demanding computing environments, and ultimately enhances the user experience.

Examples of Bus Mastering

Bus mastering is a data transfer technique where the peripheral device, such as a graphics card, network card, or storage device, takes control of the system bus (data, address, and control lines) to communicate directly with another device without involving the CPU. Here are three real-world examples of bus mastering technology:

PCI/PCI Express (Peripheral Component Interconnect): PCI and its successor, PCI Express, are common interface standards that use bus mastering technology to provide high-speed communication between peripheral devices and the CPU. One of the main advantages of these interfaces is their ability to enable high-speed data transfers while reducing the CPU’s workload. For example, a graphics card (GPU) or network interface card (NIC) with bus mastering capability can transfer data directly to other devices, like system memory or another GPU so that it’s ready for CPU processing.

Direct Memory Access (DMA): DMA is a feature of many computer systems that allows certain peripheral devices to access system memory directly without CPU intervention. This is another practical application of bus mastering technology. For instance, when transferring data to or from a hard disk drive, DMA allows the drive controller to take control of the system bus and transfer the data directly to/from the system memory, thereby saving CPU resources and speeding up the overall data transfer process.

USB (Universal Serial Bus): USB is a widely used communication protocol that allows multiple peripherals to connect to a computer or other devices. While USB does not employ bus mastering in the traditional sense, it uses a variation called ‘host-based bus mastering.’ With this variation, the host controller (usually embedded in the CPU or chipset) negotiates and manages the data transfer between USB devices, freeing the CPU to handle other tasks. In the case of USB, the host controller acts as the bus master, allowing fast and efficient communication between a variety of peripherals, such as keyboards, mice, printers, and storage devices.

Bus Mastering FAQ

What is bus mastering?

Bus mastering is a technology where a device other than the CPU has direct control of the address and data buses of the computer system. This means that the device can transfer data independently without the need for the CPU to orchestrate the transfer, reducing CPU overhead and increasing system efficiency.

What is the primary advantage of bus mastering?

The primary advantage of bus mastering is that it frees up the CPU from handling data transfers by allowing hardware devices to directly interact with the system memory. This results in a performance boost, as the CPU can focus on processing tasks rather than managing data transfers.

What devices typically use bus mastering technology?

Common devices that utilize bus mastering technology include graphics cards, network cards, RAID controllers, and other high-performance peripherals that need to rapidly transfer large volumes of data to and from the system memory.

How does bus mastering improve overall system performance?

By allowing peripheral devices to directly access the system memory and bypass the CPU, bus mastering improves overall system performance. This leads to faster data transfers, reduced latency, and a more responsive system, especially when multiple bus mastering devices are working simultaneously.

Are there any disadvantages to bus mastering?

One potential disadvantage of bus mastering is that it can introduce complexity to the system design and potentially decrease reliability. However, these issues are generally outweighed by the performance benefits gained from using bus mastering technology.

Related Technology Terms

  • Data Transfer
  • Direct Memory Access (DMA)
  • Bus Arbitration
  • Central Processing Unit (CPU)
  • Input/Output (I/O) Devices

Sources for More Information


About The Authors

The DevX Technology Glossary is reviewed by technology experts and writers from our community. Terms and definitions continue to go under updates to stay relevant and up-to-date. These experts help us maintain the almost 10,000+ technology terms on DevX. Our reviewers have a strong technical background in software development, engineering, and startup businesses. They are experts with real-world experience working in the tech industry and academia.

See our full expert review panel.

These experts include:


About Our Editorial Process

At DevX, we’re dedicated to tech entrepreneurship. Our team closely follows industry shifts, new products, AI breakthroughs, technology trends, and funding announcements. Articles undergo thorough editing to ensure accuracy and clarity, reflecting DevX’s style and supporting entrepreneurs in the tech sphere.

See our full editorial policy.

More Technology Terms

Technology Glossary

Table of Contents