bus structure

bus structure - Buses and Bus Structures Computer...

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Computer Engineering Buses and Bus Structures
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Computer Engineering BUSES • With increasing complexity of computer systems, buses are becoming one of the most important architectural elements: – Determine system performance – Impact functional diversity, modularity of design What do they do?
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Computer Engineering What do they do? Computer system consists of modules: – Processor, main memory, terminal, disk connected together through a bus! Basically set of wires that connect computer system modules/multi-processors for: • data transfers • communications
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Computer Engineering Examples of Use - Processor uses it to fetch data/instructions from main memory or store back - DMA controller uses system bus to transfer large blocks of data between main memory and disk
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Computer Engineering Types of Buses Local Buses • provide dedicated connections between CPU, RAM, ROM. . Backplane Buses - • connections between system elements (boards). Several processor independent standards exist.
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Computer Engineering Types of Buses • Computer system consists of number of modules which differ in: – transfer rates – data format – Timing characteristics • Communication requirements between components may be satisfied by dedicated , or non- dedicated bus. • What is a dedicated bus?
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Computer Engineering Dedicated Buses • Provide communication between specified pairs of devices. Advantages - since have a few, allow the exploitation of parallelism simple protocols designed to perform special functions Disadvantages - expensive less modular
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Computer Engineering Non-dedicated Buses • Several boards share the same address and data lines (wires). – This requires added address and data strobes. Advantages - – Simpler and less expensive Disadvantages - – lower throughput (all traffic goes through 1 bus) – requirement for arbitration (competition for bus)
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Computer Engineering Latency and Throughput • The delay through a non-dedicated, backplane bus increases with the number of boards included in the system. – Each transaction has to wait to get access to the bus - this is known as communication latency – The maximum throughput of the bus is independent of the number of modules attached. Thus the available throughput per module decreases .
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Computer Engineering Multiple Buses • Problem: – A single bus is a bottleneck in a computer system. ..
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Computer Engineering Multiple Buses • Solution: – Use a combination of backplane and local buses. .. CPU Memory I/O Interface CPU Memory I/O Interface Local Bus Local Bus
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Computer Engineering Local Buses • Performance of each module depends on communication latency of bus • Bus protocol: – tend to be simple, dedicated protocol (exploits parallelism), – non-standard, dedicated to a particular CPU architecture.
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Computer Engineering Backplane Buses • Allow communications over larger distances between many modules. .. • Bus protocol:
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This note was uploaded on 11/22/2010 for the course ECSE ECSE 322 taught by Professor Lowther during the Winter '04 term at McGill.

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bus structure - Buses and Bus Structures Computer...

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