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An address bus is a bus that is used to specify a physical address. When a processor or DMA-enabled device needs to read or write to a memory location, it specifies that memory location on the address bus (the value to be read or written is sent on the data bus). The width of the address bus determines the amount of memory a system can address.
A system bus is a single computer bus that connects the major components of a computer system, combining the functions of a data bus to carry information, an address bus to determine where it should be sent or read from, and a control bus to determine its operation. The technique was developed to reduce costs and improve modularity, and ...
In computer architecture, a control bus is part of the system bus and is used by CPUs for communicating with other devices within the computer. While the address bus carries the information about the device with which the CPU is communicating and the data bus carries the actual data being processed, the control bus carries commands from the CPU and returns status signals from the devices.
The Unibus was the earliest of several computer bus and backplane designs used with PDP-11 and early VAX systems manufactured by the Digital Equipment Corporation (DEC) of Maynard, Massachusetts. The Unibus was developed around 1969 by Gordon Bell and student Harold McFarland while at Carnegie Mellon University .
For example, in a computer, address information is transmitted synchronously—the address bits over the address bus, and the read or write strobes of the control bus. Single-wire synchronous signalling. A logical one is indicated when there are two transitions in the same time frame as a zero.
Multibus was an asynchronous bus that accommodated devices with various transfer rates while maintaining a maximum throughput. It had 20 address lines so it could address up to 1 Mb of Multibus memory and 1 Mb of I/O locations. Most Multibus I/O devices only decoded the first 64 Kb of address space.
When writing to memory, the CPU writes data from MDR to the memory location whose address is stored in MAR. MAR, which is found inside the CPU, goes either to the RAM (random-access memory) or cache. The MAR register is half of a minimal interface between a microprogram and computer storage; the other half is a MDR.
Often, calculating a memory address involves more than one general-purpose machine instruction, which do not necessarily decode and execute quickly. By incorporating an AGU into a CPU design, together with introducing specialized instructions that use the AGU, various address-generation calculations can be offloaded from the rest of the CPU ...