The address bus is used by a processor to indicate the memory location for reading or writing data. Peripheral controllers can share system memory with the processor using Direct Memory Access. Most PCs use a separate memory controller chip, which can create a bottleneck, but some processors have a memory controller in the main processor itself. Cache memory is often included in these processors, accessible via the cache bus.
An address bus is a computer bus used to address system main memory. In many embedded controllers and some older computers, the processor address bus is connected directly to the memory chips. Most desktop and server motherboards include the address bus in the memory bus between the memory controller chip and system memory. The address bus is used by a processor to indicate the memory location from which it is going to read or write data. Some processors may also use it to indicate an input/output port that is being read or written to.
Some computers have direct connections from the address bus of processors and other system devices to main memory. Many peripheral controllers can share system memory with the processor using a technique called Direct Memory Access (DMA). A network, hard drive, or graphics controller can be a DMA-enabled device. This allows the controller to transfer data to and from the system faster than sending it through the processor one piece at a time.
Whether the physical address comes from the processor or from a DMA device, it is hooked to the address bus. This action notifies the memory that a read or write request is about to be made for that memory address. If a write operation is in progress, the data to be written is latched onto the data bus and a memory write signal is triggered. A read operation can be performed by turning on the memory read signal and reading the data bus.
Most personal computer (PC) compatible desktops and servers use a separate memory controller chip from the main processor. This controller communicates with the main system memory via the memory bus. This bus includes the address bus, data bus, and many control signals. The memory controller is located in the northbridge device and interfaces with the main processor using the front-side bus (FSB).
The northbridge memory controller and FSB can create a bottleneck in some systems, slowing down access to processor memory. For this reason, a system’s high-speed cache memory uses an entirely separate and larger cache bus. The cache is connected directly to the processor via this bus, completely bypassing the FSB and Northbridge. The cache bus, also known as the back-side bus (BSB), functions solely as the address bus, data bus, and control bus for cache memory.
Some PC-compatible processors include a memory controller in the main processor itself. This controller accesses main system memory directly, without using the FSB or Northbridge device. With these bottlenecks removed, the processor spends less time waiting for main system memory accesses. Cache memory is also often included in these processors, and any external cache is accessible via the cache bus.
Protect your devices with Threat Protection by NordVPN
