multiprocessor system of this form will allow processes and resources such as

Multiprocessor system of this form will allow

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multiprocessor system of this form will allow processes and resources — such asmemory — to be shared dynamically among the various processors and can lowerthe workload variance among the processors. Such a system must be writtencarefully, as we shall see in Chapter 5 and Chapter 6.The definition of multiprocessorhas evolved over time and now includesmulticore systems, in which multiple computing cores reside on a single chip.Multicore systems can be more efficient than multiple chips with single coresbecause on-chip communication is faster than between-chip communication.
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1.3 Computer-System Architecture17Figure 1.8Symmetric multiprocessing architecture.In addition, one chip with multiple cores uses significantly less power than multiplesingle-core chips, an important issue for mobile devices as well as laptops.In Figure 1.9, we show a dual-core design with two cores on the same pro-cessorchip. In this design, each core has its own register set, as well as its own local cache,often known as a level 1, or L1, cache. Notice, too, that a level 2 (L2) cache is localto the chip but is shared by the two processing cores. Most archi-tectures adopt thisapproach, combining local and shared caches, where local, lower-level caches aregenerally smaller and faster than higher-level sharedFigure 1.9A dual-core design with two cores on the same chip.
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18Chapter 1 IntroductionDEFINITIONS OF COMPUTER SYSTEM COMPONENTSCPU— The hardware that executes instructions.Processor— A physical chip that contains one or moreCPUs.Core— The basic computation unit of theCPU.Multicore— Including multiple computing cores on the sameCPU.Multiprocessor— Including multiple processors.Although virtually all systems are now multicore, we use the general termCPU when referring to a single computational unit of a computer system andcore as well asmulticore when specifically referring to one or more cores onaCPU.caches. Aside from architectural considerations, such as cache, memory, and buscontention, a multicore processor with Ncores appears to the operating sys-tem as Nstandard CPUs. This characteristic puts pressure on operating-system designers —and application programmers — to make efficient use of these pro-cessing cores, anissue we pursue in Chapter 4. Virtually all modern operating systems — includingWindows, macOS, and Linux, as well as Android and iOSmobile systems — supportmulticore SMPsystems.Adding additional CPUs to a multiprocessor system will increase comput-ingpower; however, as suggested earlier, the concept does not scale very well, and oncewe add too many CPUs, contention for the system bus becomes a bottleneck andperformance begins to degrade. An alternative approach isinstead to provide each CPU(or group of CPUs) with its own local memory that isaccessed via a small, fast local bus. The CPUs are connected by a sharedsysteminterconnect, so that allCPUs share one physical address space. Thisapproach —known as
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