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This 2 page Class Notes was uploaded by Yue YU on Sunday October 11, 2015. The Class Notes belongs to CE3340.002 at University of Texas at Dallas taught by Richard Goodrum in Fall 2015. Since its upload, it has received 34 views. For similar materials see Coumputer Architecture in ComputerScienence at University of Texas at Dallas.
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Date Created: 10/11/15
Design for Moore s Law Te one constant for computer designers is rapid change which is driven largely by Moore s Law It states that integrated circuit resources double every 18 24 months Moore s Law resulted from a 1965 prediction of such growth in IC capacity made by Gordon Moore one of the founders of Intel As computer designs can take years the resources available per chip can easily double or quadruple between the start and fnish of the project Like a skeet shooter computer architects must anticipate where the technology will be when the design fnishes rather than design for where it starts We use an up and to the right Moore s Law graph to represent designing for rapid change Use Abstraction to Simplify Design Both computer architects and programmers had to invent techniques to make themselves more productive for otherwise design time would lengthen as dramatically as resources grew by Moore s Law A major productivity technique for hardware and sofware is to use abstractions to represent the design at diferent levels of representation lowerlevel details are hidden to ofer a simpler model at higher levels We ll use the abstract painting icon to represent this second great idea Make the Common Case Fast Making the common case fast will tend to enhance performance better than optimizing the rare case Ironically the common case is ofen simpler than the rare case and hence is ofen easier to enhance Tis common sense advice implies that you know what the common case is which is only possible with careful experimentation and measurement see Section 16 We use a sports car as the icon for making the common case fast as the most common trip has one or two passengers and it s surely easier to make a fast sports car than a fast minivan Performance via Parallelism Since the dawn of computing computer architects have ofered designs that get more performance by performing operations in parallel We ll see many examples of parallelism in this book We use multiple jet engines of a plane as our icon for parallel performance Performance via Pipelining A particular pattern of parallelism is so prevalent in computer architecture that it merits its own name pipelining For example before fre engines a bucket brigade would respond to a fre which many cowboy movies show in response to a dastardly act by the villain Te townsfolk form a human chain to carry a water source to fre as they could much more quickly move buckets up the chain instead of individuals running back and forth Our pipeline icon is a sequence of pipes with each section representing one stage of the pipeline Performance via Prediction Following the saying that it can be better to ask for forgiveness than to ask for permission the fnal great idea is prediction In some cases it can be faster on average to guess and start working rather than wait until you know for sure assuming that the mechanism to recover from a misprediction is not too expensive and your prediction is relatively accurate We use the fortuneteller s crystal ball as our prediction icon Hierarchy of Memories Programmers want memory to be fast large and cheap as memory speed ofen shapes performance capacity limits the size of problems that can be solved and the cost of memory today is ofen the majority of computer cost Architects have found that they can address these conficting demands with a hierarchy of memories with the fastest smallest and most expensive memory per bit at the top of the hierarchy and the slowest largest and cheapest per bit at the bottom As we shall see in Chapter 5 caches give the programmer the illusion that main memory is nearly as fast as the top of the hierarchy and nearly as big and cheap as the bottom of the hierarchy We use a layered triangle icon to represent the memory hierarchy Te shape indicates speed cost and size the closer to the top the faster and more expensive per bit the memory the wider the base of the layer the bigger the memory Dependability via Redundancy Computers not only need to be fast they need to be dependable Since any physical device can fail we make systems dependable by including redundant components that can take over when a failure occurs and to help detect failures We use the tractortrailer as our icon since the dual tires on each side of its rear axels allow the truck to continue driving even when one tire fails Presumably the truck driver heads immediately to a repair facility so the fat tire can be fxed thereby restoring redundancy
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