What is a Mezzanine Bus?

In computers, the central processing unit (CPU) acts like a brain, sending messages to different parts of the computer and other components. These signals are carried by a system of electrical sockets called a bus. CPUs are now so fast that they need more than one bus to carry information. A specialized bus that routes commands to and from the CPU to high-speed peripherals, such as memory cards, is called a mezzanine bus, or mezzanine card.

The mezzanine bus is a computer component card that sits between the motherboard and other cards. The name mezzanine comes from the word mezzano, meaning middle. The bus is a bridge that connects other cards in the computer to the CPU and allows simple, fast communication. Without a bus, the CPU would need to be hard-wired to each card and component separately.

Early computer designs used a CPU and bus that both ran at the same speed. As computers grew more sophisticated and faster, new bus systems were needed to keep pace with faster processors. Most computers now have more than one bus to handle all the information sent to and from the CPU.

Intel® created the first mezzanine bus in the 1980s. Today, most manufacturers follow a common setup for buses, called the Peripheral Component Interconnect (PCI) specification. PCI was created in the 1990s. A common type of mezzanine bus is the PCI mezzanine card (PCM).

Different PCMs are available for specific needs. Various models work with either analog or digital communications, or both. PCMs take up only one slot in the motherboard. Since slots are left over to plug in other cards, this allows the user to get more flexibility of the computer. PCMs also allow computers to use newer, faster peripherals without changing the motherboard.

Computer components and software send messages to the CPU constantly through various buses like the mezzanine bus. To handle all the CPU traffic, the buses send requests through a buffer. A buffer is an area of memory used for temporary storage.

A buffer helps the computer store, then execute requests. The buffer holds all transactions sent to and from the CPU. These requests are then completed in the order received, or according to any priority processing rules set up by the user.

Buffers are created using the computer’s random access memory (RAM). Information can be gathered faster from the RAM than from the hard drive memory. Usually, only a certain amount of RAM is allocated to a buffer. Generally, the bigger the buffer, the less RAM that is available for other tasks.