计算机英语CPU.docx

1、计算机英语CPUCentral processing unitDie of an Intel 80486DX2 microprocessor (actual size: 126.75mm) in its packaging.The central processing unit (CPU) is the portion of a computer system that carries out the instructions of a computer program, and is the primary element carrying out the computers functio

2、ns. The central processing unit carries out each instruction of the program in sequence, to perform the basic arithmetical, logical, and input/output operations of the system. This term has been in use in the computer industry at least since the early 1960s.1 The form, design and implementation of C

3、PUs have changed dramatically since the earliest examples, but their fundamental operation remains much the same.Early CPUs were custom-designed as a part of a larger, sometimes one-of-a-kind, computer. However, this costly method of designing custom CPUs for a particular application has largely giv

4、en way to the development of mass-produced processors that are made for one or many purposes. This standardization trend generally began in the era of discrete transistor mainframes and minicomputers and has rapidly accelerated with the popularization of the integrated circuit (IC). The IC has allow

5、ed increasingly complex CPUs to be designed and manufactured to tolerances on the order of nanometers. Both the miniaturization and standardization of CPUs have increased the presence of these digital devices in modern life far beyond the limited application of dedicated computing machines. Modern m

6、icroprocessors appear in everything from automobiles to cell phones and childrens toys.Contentshide 1 History o 1.1 Discrete transistor and integrated circuit CPUs o 1.2 Microprocessors 2 Operation 3 Design and implementation o 3.1 Integer range o 3.2 Clock rate o 3.3 Parallelism 3.3.1 Instruction l

7、evel parallelism 3.3.2 Thread-level parallelism 3.3.3 Data parallelism 4 Performance 5 See also 6 Notes 7 References 8 External links HistoryMain article: History of general purpose CPUsEDVAC, one of the first electronic stored program computers.Computers such as the ENIAC had to be physically rewir

8、ed in order to perform different tasks, which caused these machines to be called fixed-program computers. Since the term CPU is generally defined as a software (computer program) execution device, the earliest devices that could rightly be called CPUs came with the advent of the stored-program compu

9、ter.The idea of a stored-program computer was already present in the design of J. Presper Eckert and John William Mauchlys ENIAC, but was initially omitted so the machine could be finished sooner. On June 30, 1945, before ENIAC was completed, mathematician John von Neumann distributed the paper enti

10、tled First Draft of a Report on the EDVAC. It outlined the design of a stored-program computer that would eventually be completed in August 1949.2 EDVAC was designed to perform a certain number of instructions (or operations) of various types. These instructions could be combined to create useful pr

11、ograms for the EDVAC to run. Significantly, the programs written for EDVAC were stored in high-speed computer memory rather than specified by the physical wiring of the computer. This overcame a severe limitation of ENIAC, which was the considerable time and effort required to reconfigure the comput

12、er to perform a new task. With von Neumanns design, the program, or software, that EDVAC ran could be changed simply by changing the contents of the computers memory.While von Neumann is most often credited with the design of the stored-program computer because of his design of EDVAC, others before

13、him, such as Konrad Zuse, had suggested and implemented similar ideas. The so-called Harvard architecture of the Harvard Mark I, which was completed before EDVAC, also utilized a stored-program design using punched paper tape rather than electronic memory. The key difference between the von Neumann

14、and Harvard architectures is that the latter separates the storage and treatment of CPU instructions and data, while the former uses the same memory space for both. Most modern CPUs are primarily von Neumann in design, but elements of the Harvard architecture are commonly seen as well.As a digital d

15、evice, a CPU is limited to a set of discrete states, and requires some kind of switching elements to differentiate between and change states. Prior to commercial development of the transistor, electrical relays and vacuum tubes (thermionic valves) were commonly used as switching elements. Although t

16、hese had distinct speed advantages over earlier, purely mechanical designs, they were unreliable for various reasons. For example, building direct current sequential logic circuits out of relays requires additional hardware to cope with the problem of contact bounce. While vacuum tubes do not suffer

17、 from contact bounce, they must heat up before becoming fully operational, and they eventually cease to function due to slow contamination of their cathodes that occurs in the course of normal operation. If a tubes vacuum seal leaks, as sometimes happens, cathode contamination is accelerated. Usuall

18、y, when a tube failed, the CPU would have to be diagnosed to locate the failed component so it could be replaced. Therefore, early electronic (vacuum tube based) computers were generally faster but less reliable than electromechanical (relay based) computers.Tube computers like EDVAC tended to avera

19、ge eight hours between failures, whereas relay computers like the (slower, but earlier) Harvard Mark I failed very rarely.1 In the end, tube based CPUs became dominant because the significant speed advantages afforded generally outweighed the reliability problems. Most of these early synchronous CPU

20、s ran at low clock rates compared to modern microelectronic designs (see below for a discussion of clock rate). Clock signal frequencies ranging from 100 kHz to 4MHz were very common at this time, limited largely by the speed of the switching devices they were built with.Discrete transistor and inte

21、grated circuit CPUsCPU, core memory, and external bus interface of a DEC PDP-8/I. made of medium-scale integrated circuitsThe design complexity of CPUs increased as various technologies facilitated building smaller and more reliable electronic devices. The first such improvement came with the advent

22、 of the transistor. Transistorized CPUs during the 1950s and 1960s no longer had to be built out of bulky, unreliable, and fragile switching elements like vacuum tubes and electrical relays. With this improvement more complex and reliable CPUs were built onto one or several printed circuit boards co

23、ntaining discrete (individual) components.During this period, a method of manufacturing many transistors in a compact space gained popularity. The integrated circuit (IC) allowed a large number of transistors to be manufactured on a single semiconductor-based die, or chip. At first only very basic n

24、on-specialized digital circuits such as NOR gates were miniaturized into ICs. CPUs based upon these building block ICs are generally referred to as small-scale integration (SSI) devices. SSI ICs, such as the ones used in the Apollo guidance computer, usually contained transistor counts numbering in

25、multiples of ten. To build an entire CPU out of SSI ICs required thousands of individual chips, but still consumed much less space and power than earlier discrete transistor designs. As microelectronic technology advanced, an increasing number of transistors were placed on ICs, thus decreasing the q

26、uantity of individual ICs needed for a complete CPU. MSI and LSI (medium- and large-scale integration) ICs increased transistor counts to hundreds, and then thousands.In 1964 IBM introduced its System/360 computer architecture which was used in a series of computers that could run the same programs

27、with different speed and performance. This was significant at a time when most electronic computers were incompatible with one another, even those made by the same manufacturer. To facilitate this improvement, IBM utilized the concept of a microprogram (often called microcode), which still sees wide

28、spread usage in modern CPUs.3 The System/360 architecture was so popular that it dominated the mainframe computer market for decades and left a legacy that is still continued by similar modern computers like the IBM zSeries. In the same year (1964), Digital Equipment Corporation (DEC) introduced ano

29、ther influential computer aimed at the scientific and research markets, the PDP-8. DEC would later introduce the extremely popular PDP-11 line that originally was built with SSI ICs but was eventually implemented with LSI components once these became practical. In stark contrast with its SSI and MSI

30、 predecessors, the first LSI implementation of the PDP-11 contained a CPU composed of only four LSI integrated circuits.4Transistor-based computers had several distinct advantages over their predecessors. Aside from facilitating increased reliability and lower power consumption, transistors also all

31、owed CPUs to operate at much higher speeds because of the short switching time of a transistor in comparison to a tube or relay. Thanks to both the increased reliability as well as the dramatically increased speed of the switching elements (which were almost exclusively transistors by this time), CP

32、U clock rates in the tens of megahertz were obtained during this period. Additionally while discrete transistor and IC CPUs were in heavy usage, new high-performance designs like SIMD (Single Instruction Multiple Data) vector processors began to appear. These early experimental designs later gave rise to the era of specialized supercomputers like those made by Cray Inc.MicroprocessorsThe die from an Intel 8742Intel 80486DX2 microprocessor in a ceramic PGA package.The introduction of the microprocessor in the 1970s significantly affected t