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56-598: A multi-core processor implements multiprocessing in a single physical package. Designers may couple cores in a multi-core device tightly or loosely. For example, cores may or may not share caches , and they may implement message passing or shared-memory inter-core communication methods. Common network topologies used to interconnect cores include bus , ring , two-dimensional mesh , and crossbar . Homogeneous multi-core systems include only identical cores; heterogeneous multi-core systems have cores that are not identical (e.g. big.LITTLE have heterogeneous cores that share

112-404: A big.LITTLE core includes a high-performance core (called 'big') and a low-power core (called 'LITTLE'). There is also a trend towards improving energy-efficiency by focusing on performance-per-watt with advanced fine-grain or ultra fine-grain power management and dynamic voltage and frequency scaling (i.e. laptop computers and portable media players ). Chips designed from the outset for

168-927: A multiprocessing system, all CPUs may be equal, or some may be reserved for special purposes. A combination of hardware and operating system software design considerations determine the symmetry (or lack thereof) in a given system. For example, hardware or software considerations may require that only one particular CPU respond to all hardware interrupts, whereas all other work in the system may be distributed equally among CPUs; or execution of kernel-mode code may be restricted to only one particular CPU, whereas user-mode code may be executed in any combination of processors. Multiprocessing systems are often easier to design if such restrictions are imposed, but they tend to be less efficient than systems in which all CPUs are utilized. Systems that treat all CPUs equally are called symmetric multiprocessing (SMP) systems. In systems where all CPUs are not equal, system resources may be divided in

224-411: A multiprocessor is a computer system having two or more processing units (multiple processors) each sharing main memory and peripherals, in order to simultaneously process programs. A 2009 textbook defined multiprocessor system similarly, but noting that the processors may share "some or all of the system’s memory and I/O facilities"; it also gave tightly coupled system as a synonymous term. At

280-423: A time-sharing system ). Multiprocessing however means true parallel execution of multiple processes using more than one processor. Multiprocessing doesn't necessarily mean that a single process or task uses more than one processor simultaneously; the term parallel processing is generally used to denote that scenario. Other authors prefer to refer to the operating system techniques as multiprogramming and reserve

336-456: A SIMD engine and Picochip with 300 processors on a single die, focused on communication applications. In heterogeneous computing , where a system uses more than one kind of processor or cores, multi-core solutions are becoming more common: Xilinx Zynq UltraScale+ MPSoC has a quad-core ARM Cortex-A53 and dual-core ARM Cortex-R5. Software solutions such as OpenAMP are being used to help with inter-processor communication. Mobile devices may use

392-450: A big factor in mobile devices that operate on batteries. Since each core in a multi-core CPU is generally more energy-efficient, the chip becomes more efficient than having a single large monolithic core. This allows higher performance with less energy. A challenge in this, however, is the additional overhead of writing parallel code. Maximizing the usage of the computing resources provided by multi-core processors requires adjustments both to

448-413: A combination of cores. Embedded computing operates in an area of processor technology distinct from that of "mainstream" PCs. The same technological drives towards multi-core apply here too. Indeed, in many cases the application is a "natural" fit for multi-core technologies, if the task can easily be partitioned between the different processors. In addition, embedded software is typically developed for

504-448: A given time period, since individual signals can be shorter and do not need to be repeated as often. Assuming that the die can physically fit into the package, multi-core CPU designs require much less printed circuit board (PCB) space than do multi-chip SMP designs. Also, a dual-core processor uses slightly less power than two coupled single-core processors, principally because of the decreased power required to drive signals external to

560-466: A high speed communication system ( Gigabit Ethernet is common). A Linux Beowulf cluster is an example of a loosely coupled system. Tightly coupled systems perform better and are physically smaller than loosely coupled systems, but have historically required greater initial investments and may depreciate rapidly; nodes in a loosely coupled system are usually inexpensive commodity computers and can be recycled as independent machines upon retirement from

616-513: A large number of cores (rather than having evolved from single core designs) are sometimes referred to as manycore designs, emphasising qualitative differences. The composition and balance of the cores in multi-core architecture show great variety. Some architectures use one core design repeated consistently ("homogeneous"), while others use a mixture of different cores, each optimized for a different, " heterogeneous " role. How multiple cores are implemented and integrated significantly affects both

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672-549: A master/slave multiprocessor system of microprocessors is the Tandy/Radio Shack TRS-80 Model 16 desktop computer which came out in February 1982 and ran the multi-user/multi-tasking Xenix operating system, Microsoft's version of UNIX (called TRS-XENIX). The Model 16 has two microprocessors: an 8-bit Zilog Z80 CPU running at 4 MHz, and a 16-bit Motorola 68000 CPU running at 6 MHz. When

728-476: A new abstraction for C++ parallelism called TBB . Other research efforts include the Codeplay Sieve System , Cray's Chapel , Sun's Fortress , and IBM's X10 . Multi-core processing has also affected the ability of modern computational software development. Developers programming in newer languages might find that their modern languages do not support multi-core functionality. This then requires

784-478: A number of ways, including asymmetric multiprocessing (ASMP), non-uniform memory access (NUMA) multiprocessing, and clustered multiprocessing. In a master/slave multiprocessor system, the master CPU is in control of the computer and the slave CPU(s) performs assigned tasks. The CPUs can be completely different in terms of speed and architecture. Some (or all) of the CPUs can share a common bus, each can also have

840-405: A perceived lack of motivation for writing consumer-level threaded applications because of the relative rarity of consumer-level demand for maximum use of computer hardware. Also, serial tasks like decoding the entropy encoding algorithms used in video codecs are impossible to parallelize because each result generated is used to help create the next result of the entropy decoding algorithm. Given

896-541: A private bus (for private resources), or they may be isolated except for a common communications pathway. Likewise, the CPUs can share common RAM and/or have private RAM that the other processor(s) cannot access. The roles of master and slave can change from one CPU to another. Two early examples of a mainframe master/slave multiprocessor are the Bull Gamma 60 and the Burroughs B5000 . An early example of

952-792: A single FPGA . Each "core" can be considered a " semiconductor intellectual property core " as well as a CPU core. While manufacturing technology improves, reducing the size of individual gates, physical limits of semiconductor -based microelectronics have become a major design concern. These physical limitations can cause significant heat dissipation and data synchronization problems. Various other methods are used to improve CPU performance. Some instruction-level parallelism (ILP) methods such as superscalar pipelining are suitable for many applications, but are inefficient for others that contain difficult-to-predict code. Many applications are better suited to thread-level parallelism (TLP) methods, and multiple independent CPUs are commonly used to increase

1008-453: A single die with a unified cache, hence any two working dual-core dies can be used, as opposed to producing four cores on a single die and requiring all four to work to produce a quad-core CPU. From an architectural point of view, ultimately, single CPU designs may make better use of the silicon surface area than multiprocessing cores, so a development commitment to this architecture may carry the risk of obsolescence. Finally, raw processing power

1064-445: A soft processor at all, only use a single soft processor. However, a few designers tile as many soft cores onto an FPGA as will fit. In those multi-core systems, rarely used resources can be shared between all the cores in a cluster. While many people put exactly one soft microprocessor on a FPGA, a sufficiently large FPGA can hold two or more soft microprocessors, resulting in a multi-core processor . The number of soft processors on

1120-564: A specific hardware release, making issues of software portability , legacy code or supporting independent developers less critical than is the case for PC or enterprise computing. As a result, it is easier for developers to adopt new technologies and as a result there is a greater variety of multi-core processing architectures and suppliers. As of 2010, multi-core network processors have become mainstream, with companies such as Freescale Semiconductor , Cavium Networks , Wintegra and Broadcom all manufacturing products with eight processors. For

1176-413: A system's overall TLP. A combination of increased available space (due to refined manufacturing processes) and the demand for increased TLP led to the development of multi-core CPUs. Several business motives drive the development of multi-core architectures. For decades, it was possible to improve performance of a CPU by shrinking the area of the integrated circuit (IC), which reduced the cost per device on

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1232-399: A variety of specialty cores to run modular software scheduled by a high-level applications programming interface. [...] Atsushi Hasegawa, a senior chief engineer at Renesas , generally agreed. He suggested the cellphone's use of many specialty cores working in concert is a good model for future multi-core designs. [...] Anant Agarwal , founder and chief executive of startup Tilera , took

1288-508: Is a significant ongoing topic of research. Cointegration of multiprocessor applications provides flexibility in network architecture design. Adaptability within parallel models is an additional feature of systems utilizing these protocols. In the consumer market, dual-core processors (that is, microprocessors with two units) started becoming commonplace on personal computers in the late 2000s. Quad-core processors were also being adopted in that era for higher-end systems before becoming standard. In

1344-420: Is described by Amdahl's law . In the best case, so-called embarrassingly parallel problems may realize speedup factors near the number of cores, or even more if the problem is split up enough to fit within each core's cache(s), avoiding use of much slower main-system memory. Most applications, however, are not accelerated as much unless programmers invest effort in refactoring . The parallelization of software

1400-629: Is not the only constraint on system performance. Two processing cores sharing the same system bus and memory bandwidth limits the real-world performance advantage. The trend in processor development has been towards an ever-increasing number of cores, as processors with hundreds or even thousands of cores become theoretically possible. In addition, multi-core chips mixed with simultaneous multithreading , memory-on-chip, and special-purpose "heterogeneous" (or asymmetric) cores promise further performance and efficiency gains, especially in processing multimedia, recognition and networking applications. For example,

1456-475: The ARM big.LITTLE architecture. The research and development of multicore processors often compares many options, and benchmarks are developed to help such evaluations. Existing benchmarks include SPLASH-2, PARSEC, and COSMIC for heterogeneous systems. Multiprocessing Multiprocessing is the use of two or more central processing units (CPUs) within a single computer system . The term also refers to

1512-492: The operating system (OS) support and to existing application software. Also, the ability of multi-core processors to increase application performance depends on the use of multiple threads within applications. Integration of a multi-core chip can lower the chip production yields. They are also more difficult to manage thermally than lower-density single-core designs. Intel has partially countered this first problem by creating its quad-core designs by combining two dual-core ones on

1568-425: The operating system level, multiprocessing is sometimes used to refer to the execution of multiple concurrent processes in a system, with each process running on a separate CPU or core, as opposed to a single process at any one instant. When used with this definition, multiprocessing is sometimes contrasted with multitasking , which may use just a single processor but switch it in time slices between tasks (i.e.

1624-730: The same integrated circuit die ; separate microprocessor dies in the same package are generally referred to by another name, such as multi-chip module . This article uses the terms "multi-core" and "dual-core" for CPUs manufactured on the same integrated circuit, unless otherwise noted. In contrast to multi-core systems, the term multi-CPU refers to multiple physically separate processing-units (which often contain special circuitry to facilitate communication between each other). The terms many-core and massively multi-core are sometimes used to describe multi-core architectures with an especially high number of cores (tens to thousands). Some systems use many soft microprocessor cores placed on

1680-466: The 68000 CPU. The Z-80 can be used to do other tasks. The earlier TRS-80 Model II , which was released in 1979, could also be considered a multiprocessor system as it had both a Z-80 CPU and an Intel 8021 microcontroller in the keyboard. The 8021 made the Model II the first desktop computer system with a separate detachable lightweight keyboard connected with by a single thin flexible wire, and likely

1736-506: The IC. Alternatively, for the same circuit area, more transistors could be used in the design, which increased functionality, especially for complex instruction set computing (CISC) architectures. Clock rates also increased by orders of magnitude in the decades of the late 20th century, from several megahertz in the 1980s to several gigahertz in the early 2000s. As the rate of clock speed improvements slowed, increased use of parallel computing in

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1792-665: The Xeon processors via a common pipe and the Opteron processors via independent pathways to the system RAM . Chip multiprocessors, also known as multi-core computing, involves more than one processor placed on a single chip and can be thought of the most extreme form of tightly coupled multiprocessing. Mainframe systems with multiple processors are often tightly coupled. Loosely coupled multiprocessor systems (often referred to as clusters ) are based on multiple standalone relatively low processor count commodity computers interconnected via

1848-411: The ability of a system to support more than one processor or the ability to allocate tasks between them. There are many variations on this basic theme, and the definition of multiprocessing can vary with context, mostly as a function of how CPUs are defined ( multiple cores on one die , multiple dies in one package , multiple packages in one system unit , etc.). According to some on-line dictionaries,

1904-647: The ability to run different operating systems or OS versions on different systems. Merging data from multiple threads or processes may incur significant overhead due to conflict resolution , data consistency , versioning, and synchronization. Soft microprocessor A soft microprocessor (also called softcore microprocessor or a soft processor ) is a microprocessor core that can be wholly implemented using logic synthesis . It can be implemented via different semiconductor devices containing programmable logic (e.g., FPGA , CPLD ), including both high-end and commodity variations. Most systems, if they use

1960-662: The alternatives. An especially strong contender for established markets is the further integration of peripheral functions into the chip. The proximity of multiple CPU cores on the same die allows the cache coherency circuitry to operate at a much higher clock rate than what is possible if the signals have to travel off-chip. Combining equivalent CPUs on a single die significantly improves the performance of cache snoop (alternative: Bus snooping ) operations. Put simply, this means that signals between different CPUs travel shorter distances, and therefore those signals degrade less. These higher-quality signals allow more data to be sent in

2016-511: The bus level. These CPUs may have access to a central shared memory (SMP or UMA ), or may participate in a memory hierarchy with both local and shared memory (SM)( NUMA ). The IBM p690 Regatta is an example of a high end SMP system. Intel Xeon processors dominated the multiprocessor market for business PCs and were the only major x86 option until the release of AMD 's Opteron range of processors in 2004. Both ranges of processors had their own onboard cache but provided access to shared memory;

2072-535: The chip. Furthermore, the cores share some circuitry, like the L2 cache and the interface to the front-side bus (FSB). In terms of competing technologies for the available silicon die area, multi-core design can make use of proven CPU core library designs and produce a product with lower risk of design error than devising a new wider-core design. Also, adding more cache suffers from diminishing returns. Multi-core chips also allow higher performance at lower energy. This can be

2128-451: The cluster. Power consumption is also a consideration. Tightly coupled systems tend to be much more energy-efficient than clusters. This is because a considerable reduction in power consumption can be realized by designing components to work together from the beginning in tightly coupled systems, whereas loosely coupled systems use components that were not necessarily intended specifically for use in such systems. Loosely coupled systems have

2184-429: The count can go over 10 million (and in one case up to 20 million processing elements total in addition to host processors). The improvement in performance gained by the use of a multi-core processor depends very much on the software algorithms used and their implementation. In particular, possible gains are limited by the fraction of the software that can run in parallel simultaneously on multiple cores; this effect

2240-503: The developer's programming skills and the consumer's expectations of apps and interactivity versus the device. A device advertised as being octa-core will only have independent cores if advertised as True Octa-core , or similar styling, as opposed to being merely two sets of quad-cores each with fixed clock speeds. The article "CPU designers debate multi-core future" by Rick Merritt, EE Times 2008, includes these comments: Chuck Moore [...] suggested computers should be like cellphones, using

2296-741: The first keyboard to use a dedicated microcontroller, both attributes that would later be copied years later by Apple and IBM. In multiprocessing, the processors can be used to execute a single sequence of instructions in multiple contexts ( single instruction, multiple data or SIMD, often used in vector processing ), multiple sequences of instructions in a single context ( multiple instruction, single data or MISD, used for redundancy in fail-safe systems and sometimes applied to describe pipelined processors or hyper-threading ), or multiple sequences of instructions in multiple contexts ( multiple instruction, multiple data or MIMD). Tightly coupled multiprocessor systems contain multiple CPUs that are connected at

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2352-455: The form of multi-core processors has been pursued to improve overall processing performance. Multiple cores were used on the same CPU chip, which could then lead to better sales of CPU chips with two or more cores. For example, Intel has produced a 48-core processor for research in cloud computing; each core has an x86 architecture. Since computer manufacturers have long implemented symmetric multiprocessing (SMP) designs using discrete CPUs,

2408-416: The increasing emphasis on multi-core chip design, stemming from the grave thermal and power consumption problems posed by any further significant increase in processor clock speeds, the extent to which software can be multithreaded to take advantage of these new chips is likely to be the single greatest constraint on computer performance in the future. If developers are unable to design software to fully exploit

2464-457: The issues regarding implementing multi-core processor architecture and supporting it with software are well known. Additionally: In order to continue delivering regular performance improvements for general-purpose processors, manufacturers such as Intel and AMD have turned to multi-core designs, sacrificing lower manufacturing-costs for higher performance in some applications and systems. Multi-core architectures are being developed, but so are

2520-441: The late 2010s, hexa-core (six cores) started entering the mainstream and since the early 2020s has overtaken quad-core in many spaces. The terms multi-core and dual-core most commonly refer to some sort of central processing unit (CPU), but are sometimes also applied to digital signal processors (DSP) and system on a chip (SoC). The terms are generally used only to refer to multi-core microprocessors that are manufactured on

2576-496: The operating system of the network device. In digital signal processing the same trend applies: Texas Instruments has the three-core TMS320C6488 and four-core TMS320C5441, Freescale the four-core MSC8144 and six-core MSC8156 (and both have stated they are working on eight-core successors). Newer entries include the Storm-1 family from Stream Processors, Inc with 40 and 80 general purpose ALUs per chip, all programmable in C as

2632-408: The opposing view. He said multi-core chips need to be homogeneous collections of general-purpose cores to keep the software model simple. An outdated version of an anti-virus application may create a new thread for a scan process, while its GUI thread waits for commands from the user (e.g. cancel the scan). In such cases, a multi-core architecture is of little benefit for the application itself due to

2688-418: The other hand, on the server side , multi-core processors are ideal because they allow many users to connect to a site simultaneously and have independent threads of execution. This allows for Web servers and application servers that have much better throughput . Vendors may license some software "per processor". This can give rise to ambiguity, because a "processor" may consist either of a single core or of

2744-487: The problem, for example using a coordination language and program building blocks (programming libraries or higher-order functions). Each block can have a different native implementation for each processor type. Users simply program using these abstractions and an intelligent compiler chooses the best implementation based on the context. Managing concurrency acquires a central role in developing parallel applications. The basic steps in designing parallel applications are: On

2800-734: The resources provided by multiple cores, then they will ultimately reach an insurmountable performance ceiling. The telecommunications market had been one of the first that needed a new design of parallel datapath packet processing because there was a very quick adoption of these multiple-core processors for the datapath and the control plane. These MPUs are going to replace the traditional Network Processors that were based on proprietary microcode or picocode . Parallel programming techniques can benefit from multiple cores directly. Some existing parallel programming models such as Cilk Plus , OpenMP , OpenHMPP , FastFlow , Skandium, MPI , and Erlang can be used on multi-core platforms. Intel introduced

2856-586: The same instruction set , while AMD Accelerated Processing Units have cores that do not share the same instruction set). Just as with single-processor systems, cores in multi-core systems may implement architectures such as VLIW , superscalar , vector , or multithreading . Multi-core processors are widely used across many application domains, including general-purpose , embedded , network , digital signal processing (DSP), and graphics (GPU). Core count goes up to even dozens, and for specialized chips over 10,000, and in supercomputers (i.e. clusters of chips)

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2912-462: The single thread doing all the heavy lifting and the inability to balance the work evenly across multiple cores. Programming truly multithreaded code often requires complex co-ordination of threads and can easily introduce subtle and difficult-to-find bugs due to the interweaving of processing on data shared between threads (see thread-safety ). Consequently, such code is much more difficult to debug than single-threaded code when it breaks. There has been

2968-404: The system developer, a key challenge is how to exploit all the cores in these devices to achieve maximum networking performance at the system level, despite the performance limitations inherent in a symmetric multiprocessing (SMP) operating system. Companies such as 6WIND provide portable packet processing software designed so that the networking data plane runs in a fast path environment outside

3024-502: The system is booted, the Z-80 is the master and the Xenix boot process initializes the slave 68000, and then transfers control to the 68000, whereupon the CPUs change roles and the Z-80 becomes a slave processor responsible for all I/O operations including disk, communications, printer and network, as well as the keyboard and integrated monitor, while the operating system and applications run on

3080-489: The term multiprocessing for the hardware aspect of having more than one processor. The remainder of this article discusses multiprocessing only in this hardware sense. In Flynn's taxonomy , multiprocessors as defined above are MIMD machines. As the term "multiprocessor" normally refers to tightly coupled systems in which all processors share memory, multiprocessors are not the entire class of MIMD machines, which also contains message passing multicomputer systems. In

3136-462: The use of numerical libraries to access code written in languages like C and Fortran , which perform math computations faster than newer languages like C# . Intel's MKL and AMD's ACML are written in these native languages and take advantage of multi-core processing. Balancing the application workload across processors can be problematic, especially if they have different performance characteristics. There are different conceptual models to deal with

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