Explain what a system bus is and why it is needed

timer Asked: Apr 27th, 2014
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Question Description

Von Neumann architecture and explain why it is important. Must be 4-5 pages. Explaining what a system bus is and why it is needed. Plus more

Tutor Answer

Faiza Waqar
School: Boston College

Computer architecture is the engineering of a computer system through the careful design of its organization, using innovative mechanisms and integrating software techniques, to achieve a set of performance goals.

The most common goals in computer architecture revolve around the tradeoffs between cost and performance (i.e. speed), although other considerations, such as size, weight, reliability, feature set, expandability and power consumption, are important factors as well.

Designers of computer systems must understand the mechanisms that affect these tradeoffs throughout the system: processor instruction set, processor implementation (known as "microarchitecture"), multiprocessor organization, memory system, communication networks, input/output devices, compilers, operating systems, and application software. Courses in CAS give students a solid grounding in many of these areas, and students pursuing research have the opportunity to specialize and innovate in the areas that most interest them.

Another area of emphasis is the development of tools that enable the design of next-generation systems, such as processor simulators, full-system simulators, and computer-aided design (CAD) tools. Research in CAS typically involves a combination of experimental measurement, simulation, and analytical tools to understand and predict the behavior of complex computing systems.


The micro architecture has a unique role to play in maintaining continued performance growth, since it combines runtime knowledge of program behaviour with the ability to modify the hardware's behavior-both of which can be tracked and controlled at multiple granularities in space and time. A clear phase behavior in the SPECcpu2000 program mesa, as well as substantial temperature variation across different architectural units is shown. A dynamic compact model can be constructed using only information available in pre-RTL planning stages, namely architecture parameters, floorplan, and geometric and material properties of candidate packages. Thermal-RC pairs are constructed to represent heat flow in both the lateral and vertical directions. Power dissipation in each architecture unit is represented as a current source in the RC circuit and can be modeled using any architectural modeling tool, e.g. IBM's Power Timer. This model has been validated against Micred test chip to within 7% for both steady state and transient behavior and is boundary- and initial-condition independent (BICI). One example of "temperature-aware" architecture is dynamic thermal management (DTM) in conjunction with reducing packaging cost.

The Important of Architecture of Computer

Introduction, Why do we have to understand the organization and architecture of the computer? Without the computer architecture and computer organization now then we would not be to use great computer at this time. The basic function of a computer i.e. data processing, data storage, data transfer and controlling the data.
In order for computer functions can be implemented with either then the neccessary mechanism of computer architecture and organization proper.

In explaining the system of computer, often required the difference between computer architectures with computer organization. Computer organization is the operational design whereas computer architecture is the theory behind operational design. Why computer organization and architecture of computer required? Because computer organizations need to be designed for implement the spesifications of computer architecture as well as the addition organization as a whole also review of the architecture in detail.

For an example : The designer of computer wants to add multiplication in a computer (e.g. a computer system only have addition and subtraction system)
• Whether a computer needs to have multiply instruction is an architecture design problem.
• Whether the instruction would be implemented by special multiplication unit or by a mechanism that uses repitition adder unit is an organizational problem.

Based on the above issues then organizational decision can be based on : Frequency of use multiplication instruction, relative speed of two approaches, price, physically size multiplication special unit.

Historically and still going on to this day, the difference between computer architecture and computer organization is essential. Many computer manufacturers offer a group of computers model that all models have the same architecture but differ in terms of organization. As a result, different models will have price and performance characteristics of different well as a computer architecture can be durable, however computer organization can be changed in accordance with technological developments.

For an example, The IBM system/370 architecture. This architecture was introduced for the first time in 1970 and includes a number of models. Users who have simple needs can purchase a model which is cheaper and slower, if then needs increased, then the model can be upgraded to the more expensive models and more quickly without need replace the previous software that has been used already. In a few years, IBM has made several new models using technology that has been enhanced to replace the old model. This new model offers better speed, lower prices or both to customers. This new model maintains the same architecture so that customers who have invested capital for software can be protected.

In the class of systems called microcomputers, the relationship between organization design and architecture is very close. Technology changes not only affect the organization but also on the results that occurred architectural better and richer.

Conclusions between computer architecture and computer organization is :

Computer architecture
1. Relating to the attributes that have direct impact on logical execution of a program.
2. Architecture can endure for years or architecture changes slowly
3. Examples of architecture attribute : instruction set, number of bits, I/O mechanisms, techniques for  addressing memory.


A computer system consists of a central processing unit (CPU) for processing data, main memory to store the data being processed and multiple input and output devices. There various components have to be connected to each other for the transfer of data. A computer bus is a subsystem of the computer that makes these transfers happen. In early computer systems all transfers used actual cables. Large bundles of wires were organized using 'bus bars,' which is where the term bus comes from.

Cables are still used in present-day computer systems, in particular to connect external devices. The most common type of connection is a Universal Serial Bus (USB). Many peripheral devices, such as printers and scanners, use a USB connection. Transfers between internal components of a computer can also use cables, but some types have been replaced by integrated electronic circuitry, such as those found on a motherboard.

The most critical connection of any computer system is the system bus. This is a single computer bus that controls the transfers between the CPU, the main memory, and the input/output devices.

How the System Bus Works

The system bus carries three types of information: address, data, and control. The addressinformation describes where data is located and where it needs to go during a particular operation. The data are the actual digital pieces of information that need to be transferred. The control information manages the flow of the address and data information, including the direction of the transfer and exactly how data needs to be routed through the computer system. Because of these three different types of information, the system bus actually consists of three buses, as illustrated in the figure below.

The general design of a single system bus
computer system bus

The system bus is like the internal transportation system of your computer. Consider the following example. You want to listen to some music that is residing on your hard disk drive as an MP3 file. So the MP3 file is the data. These data have to be transferred to the sound card and converted to an analog signal so you can listen to it on your speakers. So the address information is the location of the MP3 file on your hard disk and the location of your sound card. The control information manages how this transfer is going to take place - which direction and through which components. All of this is managed by the brains of your computer (the CPU), but the system bus makes the actual transfers happen.

Hope so its use full and enough Material for You. :-)

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Good stuff. Would use again.

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