多核心cpu

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age, often a single integrated circuit (IC). A dual-core device contains only two independent microprocessors. In general, multi-core microprocessors allow a computing device to exhibit some form of thread-level parallelism (TLP) without including multiple microprocessors in separate physical packages. This form of TLP is often known as chip-level multiprocessing, or CMP. You also have to have the drives to utilize the second core in a game

There is some discrepancy in the semantics by which the terms "multi-core" and "dual-core" are defined. Most commonly they are used to refer to some sort of central processing unit (CPU), but are sometimes also applied to DSPs and SoCs. Additionally, some use these terms only to refer to multi-core microprocessors that are manufactured on the same integrated circuit die. These persons generally prefer to refer to separate microprocessor dies in the same package by another name, such as "multi-chip module", "double core", or even "twin core". This article uses both the terms "multi-core" and "dual-core" to reference microelectronic CPUs manufactured on the same integrated circuit, unless otherwise noted.-->

多核心，也叫多微处理器核心是将两个或更多的独立处理器封装在一起的方案，通常在一个集成电路（IC）中。双核心设备只有两个独立的微处理器。一般说来，多核心微处理器允许一个计算设备在不需要将多核心包括在独立物理封装时执行某些形式的线程级并行处理（Thread-Level Parallelism，TLP）这种形式的TLP通常被认为是芯片级别的多处理（Chip-level MultiProcessing，CMP）。在游戏中你必须要使用驱动程序来利用第二颗核心。

"多核心"、"双核心"的定义在字面使用中有一定差距。他们通常指某些种类的中央处理器（Central Processing Unit，CPU），但是某些时候也应用到DSP和SoC中。另外，某些情况中只适用于在同一个集成电路中的多核心微处理器。这些人将同一封装中集成的独立微处理器芯片称做“多处理模块”，“双核心”等。除非特别说明，本文将使用“多核心”指代在同一集成电路中集成的CPU。

目录

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商业化的例子

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开发动机

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技术压力

While CMOS manufacturing technology continues to improve, reducing the size of single gates, physical limits of semiconductor-based microelectronics become a major design concern. Some effects of these physical limitations can cause significant heat dissipation and data synchronization problems. The demand for more complex and capable microprocessors causes CPU designers to utilize various methods of increasing performance. Some ILP methods like superscalar pipelining are suitable for many applications, but are inefficient for others that tend to contain difficult-to-predict code. Many applications are better suited to TLP methods, and multiple independent CPUs is one common method used to increase 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 logical creation of multi-core CPUs.

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商业诱因

Several business motives drive the development of dual-core architectures. Since SMP designs have been long implemented using discrete CPUs, the issues regarding implementing the architecture and supporting it in software are well known. Additionally, utilizing a proven processing core design (e.g. Freescale's e700 core) without architectural changes reduces design risk significantly. Finally, the connotations of the terminology "dual-core" (and other multiples) lends itself to marketing efforts.

Additionally, for general-purpose processors, much of the motivation for multi-core processors comes from the increasing difficulty of improving processor performance by increasing the operating frequency (frequency-scaling). 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 the alternatives. An especially strong contender for established markets is to integrate more peripheral functions into the chip.

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优势

  • Proximity of multiple CPU cores on the same die have the advantage that the cache coherency circuitry can operate at a much higher clock rate than is possible if the signals have to travel off-chip, so combining equivalent CPUs on a single die significantly improves the performance of cache snoop operations.
  • Assuming that the die can fit into the package, physically, the multi-core CPU designs require much less Printed Circuit Board (PCB) space than multi-chip SMP designs.
  • A dual-core processor uses slightly less power than two coupled single-core processors, principally because of the increased power required to drive signals external to the chip and because the smaller silicon process geometry allows the cores to operate at lower voltages; 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.
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劣势

  • Multi-core processors do not need the operating system (OS) to support them, but instead adjustments to existing software are required to maximize the computing resources provided by multi-core processors. Also, the ability of multi-core processors to increase application performance depends on using threaded applications to optimize the use of resources.
  • Integration of a multi-core chip drives production yields down and they are more difficult to manage thermally than lower-density single-chip designs.
  • 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.
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软件影响

Most existing software is not ready to directly utilize the power of multicore processors since they are written in traditional sequential programming languages like C, C++ and FORTRAN, all of which have the limited scope of only one processor in mind.Template:Fact

Current software titles that fully utilize multi-core technologies include: Maya, Blender3D, Quake 3 & 4, Elder Scrolls: Oblivion, 3DS Max, Adobe Photoshop, Windows XP Professional, Windows 2003, Mac OS X, Linux, and many operating systems that are streamlined for server use.

Parallel programming is a must option for a single software to exploit multiple computation units(cores) simultaneously, often by multithread or multitask programming. Some existing parallel programming models such as OpenMP and MPI can be directly used on multi-core platforms. Other research efforts have been seen also, like Cray’s Chapel, Sun’s Fortress, and IBM’s X10.

Concurrency acquires a central role in true parallel application. The basic steps in designing parallel applications are:

Partitioning 
The partitioning stage of a design is intended to expose opportunities for parallel execution. Hence, the focus is on defining a large number of small tasks in order to yield what is termed a fine-grained decomposition of a problem.
Communication 
The tasks generated by a partition are intended to execute concurrently but cannot, in general, execute independently. The computation to be performed in one task will typically require data associated with another task. Data must then be transferred between tasks so as to allow computation to proceed. This information flow is specified in the communication phase of a design.
Agglomeration 
In the third stage, we move from the abstract toward the concrete. We revisit decisions made in the partitioning and communication phases with a view to obtaining an algorithm that will execute efficiently on some class of parallel computer. In particular, we consider whether it is useful to combine, or agglomerate, tasks identified by the partitioning phase, so as to provide a smaller number of tasks, each of greater size. We also determine whether it is worthwhile to replicate data and/or computation.
Mapping 
In the fourth and final stage of the parallel algorithm design process, we specify where each task is to execute. This mapping problem does not arise on uniprocessors or on shared-memory computers that provide automatic task scheduling.

On the other hand, on the server side, multicore 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.

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许可

Another issue is the question of software licensing for multi-core CPUs. Typically enterprise server software is licensed "per processor". In the past a CPU was a processor (and moreover most computers had only one CPU) and there was no ambiguity. Now there is the possibility of counting cores as processors and charging a customer for two licenses when they use a dual-core CPU. However, the trend seems to be counting dual-core chips as a single processor as Microsoft, Intel, and AMD support this view. Oracle counts AMD and Intel dual-core CPUs as a single processor but has other numbers for other types. IBM, HP and Microsoft count a multi-chip module as multiple processors. If multi-chip modules counted as one processor then CPU makers would have an incentive to make large expensive multi-chip modules so their customers saved on software licensing. So it seems that the industry is slowly heading towards counting each die (see Integrated circuit) as a processor, no matter how many cores each die has. Intel has released Paxville which is really a multi-chip module but Intel is calling it a dual-core. It is not clear yet how licensing will work for Paxville. This is an unresolved and thorny issue for software companies and customers.

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普遍误解

Many people commonly assume that the multithreading benefits of a dual-core processor will translate into a better user experience while multitasking. This is not generally true, as many user applications (such as word processing applications) spend most of their time in an idle state; a person can't switch contexts faster than a computer. The improvements in computer responsiveness are generally a function of the operating system and the application code; many applications are not pervasively multithreaded since coding multithreaded applications is generally considered to be very difficult.

随着近日英特尔、AMD推出各种双核CPU新品，“双核”概念在业内逐渐升温。有意思的是，虽然都是双核，英特尔和AMD确各谈各的。英特尔大谈双核到桌面，AMD则直取双核的服务器市场。这两个公司双核到底有什么不同呢？以下是关于双核技术的背景资料，供大家参考。

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AMD、Intel双核之争

最近逐渐热起来的“双核”概念，主要是指基于X86开放架构的双核技术。在这方面，起领导地位的厂商主要有AMD和Intel两家。其中，两家的思路又有不同。AMD从一开始设计时就考虑到了对多核心的支持。所有组件都直接连接到CPU，消除系统架构方面的挑战和瓶颈。两个处理器核心直接连接到同一个内核上，核心之间以芯片速度通信，进一步降低了处理器之间的延迟。而Intel采用多个核心共享前端总线的方式。专家认为，AMD的架构对于更容易实现双核以至多核，Intel的架构会遇到多个内核争用总线资源的瓶颈问题。

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AMD和Intel不同的体系结构

双核与双芯(Dual Core Vs. Dual CPU)

AMD和Intel的双核技术在物理结构上也有很大不同之处。AMD将两个内核做在一个Die(内核)上，通过直连架构连接起来，集成度更高。Intel则是采用两个独立的内核封装在一起，因此有人将Intel的方案称为“双芯”，认为AMD的方案才是真正的“双核”。

从用户端的角度来看，AMD的方案能够使双核CPU的管脚、功耗等指标跟单核CPU保持一致，从单核升级到双核，不需要更换电源、芯片组、散热系统和主板，只需要刷新BIOS软件即可，这对于主板厂商、计算机厂商和最终用户的投资保护是非常有利的。

客户可以利用其现有的90纳米基础设施，通过BIOS更改移植到基于双核心的系统。计算机厂商可以轻松地提供同一硬件的单核心与双核心版本，使那些既想提高性能又想保持IT环境稳定性的客户能够在不中断业务的情况下升级到双核心。在一个机架密度较高的环境中，通过在保持电源与基础设施投资不变的情况下移植到双核心，客户的系统性能将得到巨大的提升。在同样的系统占地空间上，通过使用双核心处理器，客户将获得更高水平的计算能力和性能。

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双核处理器的评价标准

性能和环保是双核处理器的评价标准。

推出双核处理器架构是2005年x86处理器市场的一件大事。经过去年的市场预热期后，2006年双核市场出现的一个明显现象，上游的芯片厂商进一步加强了双核的推广力度，无论是市场宣传和推广还是价格上，都有了进一步的动作。近期英特尔和AMD的“真假双核”之争，起到了市场宣传的作用，客观上加快了双核概念在消费者中的认知。

从处理器对双核的实现方式来说，可使用两个核心直连，共用缓存，也可利用多芯片封装技术，直接将两颗芯片封装在一起，从这个角度说，双核心直连来得更彻底些。但无论是多芯片封装技术还是直连核心，是用户看不到的。如果说双核判断有标准的话，那就是更好的性能，更加环保的能耗。用户需要的是性能好、能耗低、稳定安全的处理器平台。纵观处理器的发展方向，从浮点运算到多媒体处理能力的加强，从主频提升到降低电压，这些处理器技术革新无不是从更加良好的性能和更加环保的特征进化。对于新出现的双核处理器，也应该本着性能和环保来评价其优越性。所以，比较的本质是什么样的处理器能够通过更好的性能和更加环保的特征，将产品本身和用户使用体验带入一个新的阶段。

双核处理器的争论实际上是双方对双核进行的市场宣传，客观上加快了双核概念在消费者中的认知。双核处理器的评价标准应该从用户的角度出发而不是单纯的技术，性能和环保因素是评价双核处理器的标准。

摘自：易观往 www.analysys.com.cn

为什么IBM、HP等厂商的双核产品无法实现普及呢，因为它们相当昂贵的，从来没得到广泛应用。比如拥有128MB L3缓存的双核心IBM Power4处理器的尺寸为115x115mm，生产成本相当高。因此，我们不能将IBM Power4和HP PA8800之类双核心处理器称为AMD即将发布的双核心处理器的前辈。

目前，x86双核处理器的应用环境已经颇为成熟，大多数操作系统已经支持并行处理，目前大多数新或即将发布的应用软件都对并行技术提供了支持，因此双核处理器一旦上市，系统性能的提升将能得到迅速的提升。因此，目前整个软件市场其实已经为多核心处理器架构提供了充分的准备。

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多核处理器的创新意义

1去 x86多核处理器标志着计算技术的一次重大飞跃。这一重要进步发生之际，正是企业和消费者面对飞速增长的数字资料和互联网的全球化趋势，开始要求处理器提供更多便利和优势之时。多核处理器，较之当前的单核处理器，能带来更多的性能和生产力优势，因而最终将成为一种广泛普及的计算模式。多核处理器还将在推动PC安全性和虚拟技术方面起到关键作用，虚拟技术的发展能够提供更好的保护、更高的资源使用率和更可观的商业计算市场价值。普通消费者也将比以往拥有更多的途径获得更高性能，从而提高他们家用PC和数字媒体计算系统的使用。

在单一处理器上安置两个或更多强大的计算核心的创举开拓了一个全新的充满可能性的世界。多核心处理器可以为战胜今天的处理器设计挑战提供一种立竿见影、经济有效的技术――降低随着单核心处理器的频率(即“时钟速度”)的不断上升而增高的热量和功耗。多核心处理器有助于为将来更加先进的软件提供卓越的性能。现有的操作系统(例如MS Windows、Linux和Solaris)都能够受益于多核心处理器。在将来市场需求进一步提升时，多核心处理器可以为合理地提高性能提供一个理想的平台。因此，下一代软件应用程序将会利用多核处理器进行开发。无论这些应用是否能帮助专业动画制作公司更快更节省地生产出更逼真的电影，或开创出突破性的方式生产出更自然更富灵感的PC机，使用多核处理器的硬件所具有的普遍实用性都将永远地改变这个计算世界。

虽然双核甚至多核芯片有机会成为处理器发展史上最重要的改进之一。需要指出的是，双核处理器面临的最大挑战之一就是处理器能耗的极限!性能增强了，能量消耗却不能增加。根据著名的汤氏硬件网站得到的文件显示，代号Smithfield的CPU热设计功耗高达130瓦，比现在的Prescott处理器再提升13%。由于今天的能耗已经处于一个相当高的水平，我们需要避免将CPU作成一个“小型核电厂”，所以双核甚至多核处理器的能耗问题将是考验AMD与Intel的重要问题之一。

关于多核处理器，从全球范围内看，AMD在对客户的理解和对输出最符合客户需求的产品方面的理念走在Intel的前面，从上世纪九十年代起就一直计划着这一重大进展，它第一个宣布了在单处理器上安置多个核心的想法。


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备注

  1. Template:Note Digital signal processors, DSPs, have utilized dual-core architectures for much longer than high-end general purpose processors. A typical example of a DSP-specific implementation would be a combination of a RISC CPU and a DSP MPU. This allows for the design of products that require a general purpose processor for user interfaces and a DSP for real-time data processing; this type of design is suited to e.g. mobile phones.
  2. Template:Note Two types of operating systems are able to utilize a dual-CPU multiprocessor: partitioned multiprocessing and symmetric multiprocessing (SMP). In a partitioned architecture, each CPU boots into separate segments of physical memory and operate independently; in an SMP OS, processors work in a shared space, executing threads within the OS independently.
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参见

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外部链接

取自"http://wiki.ccw.com.cn/%E5%A4%9A%E6%A0%B8%E5%BF%83cpu"