Address bus definition

In computer architecture, a bus is a communication system that transfers data between components within a computer. This article deals specifically with the address bus within microprocessors.

The address bus is the microprocessor bus independent of the data bus where the memory address of the data in transit is established.

Other buses

* databus

* control bus

Simplified diagram of a computer system implemented with a single system bus. This modular organization was popular in the 1970s and 1980s.

address bus

RAM memory is addressable, so each memory cell has its own address. Addresses are a number that selects a memory cell within main memory or in the address space of the input/output unit.

The address bus is a completely independent microprocessor channel from the data bus where the memory address of the data in transit is established.

The address bus consists of the set of electrical lines necessary to establish an address. The capacity of the memory that can be addressed depends on the number of bits that make up the address bus, with 2^n being the maximum size in bits of the memory bank that can be addressed with n lines.

Let’s see an example, to address a 256-bit memory, at least 8 lines are necessary, since 2 raised to 8 = 256. Additionally, control lines may be necessary to indicate when the address is available on the bus. This depends on the design of the bus itself.

Control bus vs data bus vs address bus

While the address bus carries information about what device the CPU is communicating with, the data bus carries the data that is actually being processed, while the control bus carries commands from the CPU and returns signals from the CPU. status from the device.

In other words, the control bus is the one that manages the use and access to the data and address lines. These lines are shared by all components, therefore there must be mechanisms that control them to avoid information collisions. Therefore the control signals transmit both commands and timing information between the modules.

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