Definitions of Multiprocessors in Computing

Definitions of Multi mainframe computers in ComputingA multi actionor dirty dog be defined as the computer which dos two or more impact units to a lower place the integrated control. Multi-processing is also defined as the way of using two or more than two CPUs within a champion computer. As we both in all know that there are central processing units inside the computers, the multi processors, as the name indicates, have the ability to support more than cardinal processor at a like time. Usually in multi-processing the processors are organized in the parallel form and hence a large number of the proceedings can be brought at the uniform time i.e. multi-processing helps in executing the alike instructions a number of time at a particular time. Some former(a) related comment of the multi processors are that multi-processing is the sharing of the execution process by the interconnectedness of more than one microprocessor using tightly or loosely couples technology. Usuall y multi-processing tasks carries two coincidental steps. One is the performing the task of editing and the other is the handling the info processing. A multi-processor device comprising, all over a wizard semiconductor chip a plurality of processors including a first group of processors and a twinkling group of processors a first stack to which the first group of processors is join a second bus to which the second group of processors is coupled a first immaterial bus interface to which the first bus is coupled and a second external bus interface to which the second bus is coupled. The term multiprocessing is also used to refer to a computer that has many independent processing elements. The processing elements are almost full computers in their own right. The main difference is that they have been freed from the encumbrance of communication with peripherals.MULTIPROCESSORS IN THE TERMS OF ARCHITECTUREThe processors are unremarkably made up of the small and medium scale IC s which usually contains a less or large number of the transistors. The multi processors involves a computer architecture close to common multiprocessor systems today use an SMP architecture. In the case of multi-core processors, the SMP architecture applies to the cores, treating them as separate processors. SMP systems allow any processor to run for on any task no matter where the info for that task are located in stock with proper run system support, SMP systems can easily move tasks in the midst of processors to balance the workload efficiently.Benefits change magnitude processing powerScale resource use to application requirementsAdditional operating system responsibilitiesAll processors remain busybodiedEven distri preciselyion of processes throughout the systemAll processors work on consistent copies of shared dataExecution of related processes synchronizedMutual exception enforcedMultiprocessing is a type of processing in which two or more processors work together t o process more than one plan simultaneously. Multi processor systems have more than one processor thats why known as multi processor systems.In multiprocessor system there is one master processor and other are the Slave. If one processor fails then master can assign the task to other slave processor. But if sea captain will be fail than entire system will fail. Central part of Multiprocessor is the Master. All of them share the hard disk and Memory and other store devices.Examples of multiprocessors1. Quad-Processor Pentium ProSMP, bus interconnection.4 x 200 MHz Intel Pentium Pro processors.8 + 8 Kb L1 cache per processor.512 Kb L2 cache per processor.Snoopy cache coherence.Compaq, HP, IBM, NetPower.Windows NT, Solaris, Linux, etc.2. SGI inception 2000NUMA, hypercube interconnection.Up to 128 (64 x 2) MIPS R 10000 processors.32 + 32 Kb L1 cache per processor.4 Mb L2 cache per processor.Distributed directory-based cache coherence.Automatic page migration/replication.SGI IRIX wi th P wanderClassifications of multiprocessor architectureNature of data pathInterconnection schemeHow processors share resourcesMessage-Passing ArchitecturesSeparate book of facts quadruplet for each processor.Processors run via message passing.B) Shared-Memory ArchitecturesSingle address space shared by all processors.Processors communicate by retentivity read/write.SMP or NUMA.Cache coherence is important issue.1. Classifying Sequential and Parallel Architectures(DATA PATH) catamenia sequence of bytesData streamInstruction streamFlynns classificationsMISD multiprocessing MISD multiprocessing offers mainly the advantage of redundancy, since multiple processing units perform the same tasks on the same data, reducing the chances of incorrect results if one of the units fails. MISD architectures may involve comparisons mingled with processing units to detect failures. Apart from the redundant and fail-safe character of this type of multiprocessing, it has few advantages, and it is truly expensive. It does not improve performance. It can be implemented in a way that is transparent to software. It is used inarray processorsand is implemented in fault tolerant machines.MIMD multiprocessing MIMD multiprocessing architecture is suitable for a wide variety of tasks in which completely independent and parallel execution of instructions touching different sets of data can be put to productive use. For this reason, and because it is easy to implement, MIMD predominates in multiprocessing.Processing is divided into multiplethreads, each with its own hardware processor state, within a single software-defined process or within multiple processes. Insofar as a system has multiple threads awaiting dispatch (either system or user threads), this architecture makes good use of hardware resources.MIMD does raise issues of deadlock and resource contention, however, since threads may collide in their admission price to resources in an unpredictable way that is demanding to m anage efficiently. MIMD requires special coding in the operating system of a computer but does not require application changes unless the programs themselves use multiple threads (MIMD is transparent to single-threaded programs under most operating systems, if the programs do not voluntarily relinquish control to the OS). Both system and user software may charter to use software constructs such assemaphores(also called locksorgates) to prevent one thread from interfering with another if they should happen to cross paths in referencing the same data. This gating or locking process increases code complexity, lowers performance, and greatly increases the amount of testing required, although not usually enough to negate the advantages of multiprocessing.Similar conflicts can arise at the hardware level between processors (cache contention and corruption, for example), and must usually be resolved in hardware, or with a combination of software and hardware (e.g.,cache-clear instructions ).SISD multiprocessing In asingle instruction stream, single data streamcomputer one processor sequentially processes instructions, each instruction processes one data item.SIMD multiprocessing In asingle instruction stream, multiple data streamcomputer one processor handles a stream of instructions, each one of which can perform calculations in parallel on multiple data locations. SIMD multiprocessing is well suited toparallel or vector processing, in which a very large set of data can be divided into parts that are individually subjected to identical but independent operations. A single instruction stream directs the operation of multiple processing units to perform the same manipulations simultaneously on potentially large amounts of data. For received types of computing applications, this type of architecture can produce enormous increases in performance, in terms of the elapsed time required to complete a wedded task. However, a drawback to this architecture is that a large p art of the system falls idle when programs or system tasks are executed that cannot be divided into units that can be processed in parallel.2. Interconnection schemeDescribes how the systems components, such as processors and memory modules, are connectedConsists of nodes (components or switches) and links (connections)Parameters used to evaluate interconnection schemesNode degreeBisection widthNetwork diameterCost of the interconnection schemeShared busSingle communication path between all nodesContention can build up for shared busFast for small multiprocessorsForm supernodes by connecting several components with a shared bus use a more scalable interconnection scheme to connect supernodesDual-processor Intel PentiumShared bus multiprocessor organization.Crossbar-switch intercellular substanceSeparate path from every processor to every memory module (or from every to every other node when nodes consist of both processors and memory modules)High fault tolerance, performance and cos tSun UltraSPARC-IIICrossbar-s witch ground substance multiprocessor organization.Hypercuben -dimensional hypercube has 2 nodes in which each node is n connected to n neighbor nodesFaster, more fault tolerant, but more expensive than a 2-D mesh networkn CUBE (up to 8192 processors)Multistage networkSwitch nodes act as hubs routing messages between nodesCheaper, less fault tolerant, worse performance compared to a crossbar-switch matrixIBM POWER4COUPLING of PROCESSORSTightly coupled systemsProcessors share most resources including memoryCommunicate over shared buses using shared carnal memoryTasks and/or processors communicate in a bluely synchronized fashionCommunicates through a common shared memoryShared memory systemLoosely coupled systemsProcessors do not share most resourcesMost communication through explicit messages or shared virtual memory (although not shared physical memory)Tasks or processors do not communicate in a synchronized fashionCommunicates by message passing pa cketsOverhead for data exchange is highDistributed memory systemComparison between themLoosely coupled systems more flexible, fault tolerant, scalableTightly coupled systems more efficient, less burden to operating system programmersMultiprocessor Operating System OrganizationsClassify systems based on how processors share operating system responsibilitiesTypesMaster/slaveSeparate kernelsSymmetrical organization1) Master/slave organizationMaster processor executes the operating systemSlaves execute only user processorsHardware asymmetryLow fault tolerance fair for computationally intensive jobs2) Separate kernels organizationEach processor executes its own operating systemSome world-widely shared operating system dataLoosely coupledCatastrophic failure unlikely, but failure of one processor results in termination of processes on that processorLittle contention over resourcesExample Tandem system3) Symmetrical organizationOperating system manages a pool of identical processorsHigh a mount of resource sharing hire for mutual exclusionHighest degree of fault tolerance of any organizationSome contention for resourcesExample BBN ButterflyMemory Access ArchitecturesCan associate multiprocessors based on how processors share memoryGoal Fast memory access from all processors to all memoryContention in large systems makes this aery1) Uniform memory access (UMA) multiprocessorAll processors share all memoryAccess to any memory page is nearly the same for all processors and all memory modules (disregarding cache hits)Typically uses shared bus or crossbar-switch matrixAlso called symmetric multiprocessing (SMP)Small multiprocessors (typically two to eight processors)2) Nonuniform memory access (NUMA) multiprocessorEach node contains a few processors and a portion of system memory, which is local to that nodeAccess to local memory faster than access to global memory (rest of memory)to a greater extent scalable than UMA (fewer bus collisions)3) Cache-only memory architect ure (COMA) multiprocessorPhysically interconnected as a NUMA isLocal memory vs. global memoryMain memory is viewed as a cache and called an attraction memory (AM)Allows system to migrate data to node that most often accesses it at granularity of a memory line (more efficient than a memory page)Reduces the number of cache misses serviced remotelyOverheadDuplicated data itemsComplex protocol to crack all updates are received at all processors4) No-remote-memory-access (NORMA) multiprocessorDoes not share physical memorySome implement the illusion of shared physical memory shared virtual memory (SVM)Loosely coupledCommunication through explicit messagesDistributed systemsNot networked systemFeatures of the multiprocessorsMany multiprocessors share one address spaceThey conceptually share memory.Sometimes it is often implemented just like a multicomputerIn it the communication is implicit. It reads and writes access to the shared memories.Usually the multi processors are characterized by the complex behaviour.The MPU handles high-level tasks, including axis profile generation, host/controller communication, user-program execution, and safety event handling.Advanced real time algorithm and special filter executionDigital encoder input up to 20 million counts per secondAnalog Sin-Cos encoder input and interpolation up to a multiplication factor of 65,536Fast, high-rate Position grammatical case Generator (PEG) to trigger external devicesFast position registration (Mark) to capture position on input eventHigh resolution analog or PWM command generation to the driveHigh Speed Synchronous Interface channel (HSSI) to manage fast communication with remote axes or I/O expansion modulesAdvantages of Multiprocessor SystemsSome advantages of multiprocessor system are as followsReduced Cost Multiple processors share the same resources. Separate power supply or fuss board for each chip is not required. This reduces the cost.Increased Reliability The reliability of system is also increased. The failure of one processor does not affect the other processors though it will slow down the machine. Several mechanisms are required to achieve increased reliability. If a processor fails, a job running on that processor also fails. The system must be able to reschedule the failed job or to alert the user that the job was not successfully completed.More work As we increase the number of processors then it means that more work can be done in less time. Id more than one processor cooperates on a task then they will take less time to complete it.If we divide functions among several processors, then if one processor fails then it will not affect the system or we can say it will not halt the system, but it will effect on the work speed. Suppose I have five processors and one of them fails due to some reasons then each of the remaining four processors will share the work of failed processor. So it means that system will not fail but definitely failed processor will eff ect on its speed.If you pay attention on the matter of which save much money among multi-processor systems and multiple single-processor systems then you will know that multiprocessor systems save moremoneythan multiple single-processor systems because they can share power supplies, memory and peripherals.Increased Throughput An increase in the number of processes completes the work in less time. It is important to note that doubling the number of processors does not halve the time to complete a job. It is due to the overhead in communication between processors and contention for shared resources etc.ReferenceBOOKS ReferredMorris Mano, Computer System Architecture, Prentice Hall, 2007