工程力學(xué)專業(yè)英語翻譯PPT課件

1、.,1,Translation The concepts of stress and strain can be illustrated in an elementary way by considering the extension of a prismatic bar. As shown in Fig. 1, a prismatic bar is one that has constant cross section throughout its length and a straight axis. In this illustration the bar is assumed to

2、be loaded at its ends by axial forces P that produce a uniform stretching, or tension, of the bar.,應(yīng)力和應(yīng)變的概念可以通過考慮一根矩形梁的拉伸的簡單方法來舉例說明。如圖1所示，這根矩形梁可以看作是由遍及長度方向的連續(xù)橫截面所組成，這些橫截面垂直于它的軸向。在這個(gè)例子中，這根矩形梁被假定在它兩端施加了一對(duì)使它發(fā)生均勻拉伸的軸向力P。,.,2,By making an artificial cut (section mm) through the bar at right angles to its

3、 axis, we can isolate part of the bar as a free body see Fig.1(b). At the left-hand end the tensile force P is applied, and at the other end there are forces representing the action of the removed portion of the bar upon the part that remains. These forces will be continuously distributed over the p

4、art cross section, analogous to the continuous distribution of hydrostatic pressure over a submerged surface.,假設(shè)在梁的軸向上做一個(gè)垂直截面（截面mm），可以分離出一部分自由的梁見圖1(b)。在該梁的左端，有拉力P，而在另一端有相應(yīng)的力可以替代梁的分離部分對(duì)它的作用。這些力連續(xù)分布在橫截面上，類似于在水平面下的靜水壓力的連續(xù)分布。,.,3,The intensity of force, that is, the force per unit area, is called the st

5、ress and is commonly denoted by the Greek letter . Assuming that the stress has a uniform distribution over the cross section see Fig.1(b), we can readily see that its resultant is equal to the intensity times the cross-sectional area A of the bar. Furthermore, from the equilibrium of the body shown

6、 in Fig.1(b), we can also see that this resultant must be equal in magnitude and opposite in direction to the force P. Hence, we obtain = P/A. (1),力的強(qiáng)度，也就是說單位面積上的力，被稱為應(yīng)力，通常用希臘字母來表示。假定應(yīng)力在橫截面上均勻分布見圖1 ( b )，那么我們可以很容易的看出它的合力等于強(qiáng)度乘以梁的橫截面積A。而且，從圖1上顯示的物體的平衡來看，我們可以發(fā)現(xiàn)這個(gè)合力是跟拉力P在數(shù)值上相等，方向相反的。因此，我們得到方程（1） = P/A。,

7、.,4,Eq.(1) can be regarded as the equation for the uniform stress in a prismatic bar. This equation shown that stress has units of force divided by area. When the bar is being stretched by the force P , as shown in the figure, the resulting stress is a tensile stress; if the forces are reversed in d

8、irection, causing the bar to be compressed, they are called compressive stress.,方程(1) 用于求解在梁中均勻分布的應(yīng)力問題。它表示了應(yīng)力的單位是力除以面積。正如我們?cè)趫D1中所看到的，當(dāng)梁被力P拉伸的時(shí)候，生成的應(yīng)力是拉應(yīng)力；如果力的方向被顛倒，導(dǎo)致梁被壓縮時(shí)，產(chǎn)生的應(yīng)力被稱為壓應(yīng)力。,.,5,A necessary condition for Eq.(1) to be valid is that the stress must be uniform over the cross section of the ba

9、r. This condition will be realized if the axial force P acts through the centroid of the cross section. When the load P does not act at the centroid, bending of the bar will result, and a more complicated analysis is necessary. At present, however, it is assumed that all axial forces are applied at

10、the centroid of the cross section unless specifically stated to the contrary. Also, unless stated otherwise, it is generally assumed that the weight of the object itself is neglected, as was done when discussing the bar in Fig.1.,方程(1) 成立的必要條件是應(yīng)力在梁的橫截面上是均勻分布的。如果軸向力P通過橫截面的形心，那么這個(gè)條件是可以實(shí)現(xiàn)的。如果軸向力P不通過橫截面

11、的形心，則會(huì)導(dǎo)致梁的彎曲，必須經(jīng)過更復(fù)雜的分析。然而，目前除非特定說明，都假定所有的軸向力都通過橫截面的形心。同樣，除非是另外說明，一般我們不考慮物體自重，正如我們?cè)趫D1中討論的梁一樣。,.,6,The total elongation of a bar carrying an axial force will be denoted by the Greek letter see Fig.1(a), and the elongation per unit length, or strain, is then determined by the equation =/L (2). Where L

12、 is the total length of the bar. Note that the strain is a non-dimensional quantity. It can be obtained accurately from Eq.(2) as long as the strain is uniform throughout the length of the bar. If the bar is in tension, the strain is a tensile strain, representing an elongation or stretching of the

13、material; if the bar is in compression, the strain is a compressive strain, which means that adjacent cross section of the bar move closer to one another.,在軸向力作用下，梁的總伸長用希臘字母來表示見圖1(a)，單位伸長量或者說應(yīng)變將由方程(2)決定，這里L(fēng)是指梁的總長度。注意，這里應(yīng)變是一個(gè)無量綱量，只要應(yīng)變?cè)诹旱拈L度上各處是均勻的，那么它可以通過方程(2)精確獲得。如果梁被拉伸，那么得到拉應(yīng)變，表現(xiàn)為材料的延長或者拉伸；如果梁被壓縮，那么

14、得到壓應(yīng)變，意味著梁的橫截面將彼此更加靠近。,.,7,When a material exhibits a linear relationship between stress and strain, it is said to be linear elastic. This is an extremely important property of many solid materials, including most metals, plastics, wood, concrete, and ceramics. The linear relationship between stress

15、 and strain for a bar in tension can be expressed by the simple equation =E (3) in which E is a constant of proportionality known as the modulus of elasticity for the material.,當(dāng)一種材料的應(yīng)力與應(yīng)變表現(xiàn)出線性關(guān)系時(shí)，我們稱這種材料為線彈性材料。這是許多固體材料的一個(gè)極其重要的性質(zhì)，這些材料包括大多數(shù)金屬，塑料，木材，混凝土和陶瓷。對(duì)于被拉伸的梁來說，這種應(yīng)力與應(yīng)變之間的線性關(guān)系可以用簡單方程(3) = E 來表示，這里

16、E是一個(gè)已知的比例常數(shù)，即該材料的彈性模量。,.,8,Note that E has the same units as stress. The modulus of elasticity is sometimes called Youngs modulus, after the English scientist Thomas Young (1773-1829) who studied the elastic behavior of bars. For most materials the modulus of elasticity in compression is the same as

17、 in tension.,注意，彈性模量的單位跟應(yīng)力的單位相同。在研究梁的彈性行為的英國科學(xué)家Thomas Young (1773-1829)出現(xiàn)之后，彈性模量有時(shí)也被稱為楊氏模量。對(duì)大多數(shù)材料而言，壓縮和拉伸時(shí)的彈性模量是一樣的。,.,9,Translation,The relationship between stress and strain in a particular material is determined by means of a tensile test. A specimen of the material, usually in the form of a roun

18、d bar, is placed in a testing machine and subjected to tension. The force on the bar and the elongation of the bar are measured as the load is increased. The stress in the bar is found by dividing the force by the cross-sectional area, and the strain is found by dividing the elongation by the length

19、 along which the elongation occurs. In this manner a complete stress-strain diagram can be obtained for the material.,一種材料的應(yīng)力-應(yīng)變關(guān)系可以通過一個(gè)拉伸測試來確定。材料的樣品通常做成圓棒狀，放置在測試儀器上然后施加拉力。隨著載荷的增加，圓棒受的力和伸長量可以被測定。圓棒的應(yīng)力可以通過力除以橫截面積得到，應(yīng)變則通過伸長量除以圓棒的長度得到。這樣，我們就得到了這種材料完整的應(yīng)力-應(yīng)變圖表。,.,10,The typical shape of the stress-strain

20、 diagram for structural steel is shown in Fig. 1, where the axial strains are plotted on the horizontal axis and the corresponding stresses are given by the ordinates to the curve OABCDE. From O to A the stress and the strain are directly proportional to one another and the diagram is linear. Beyond

21、 point A the linear relationship between stress and strain no longer exists, hence the stress at A is called the proportional limit.,圖1是結(jié)構(gòu)鋼的經(jīng)典應(yīng)力-應(yīng)變圖，圖中橫坐標(biāo)表示軸向的應(yīng)變，跟通過縱坐標(biāo)表示的相應(yīng)的應(yīng)力一起形成曲線OABCDE。從O到A這一段，應(yīng)力和應(yīng)變彼此成正比關(guān)系，圖形是成線性的。超過A點(diǎn)以后，應(yīng)力和應(yīng)變的線性關(guān)系不再存在，因此A點(diǎn)的應(yīng)力被稱為比例極限。,.,11,With an increase in loading, the strain

22、 increases more rapidly than the stress, until at point B a considerable elongation begins to occur with no appreciable increase in the tensile force. This phenomenon is known as yielding of the material, and the stress at point B is called the yield point or yield stress. In the region BC the mater

23、ial is said to have become plastic, and the bar may actually elongate plastically by an amount which is 10 or 15 times the elongation which occurs up to the proportional limit.,隨著載荷的增加，應(yīng)變的增長比應(yīng)力更快，直到B點(diǎn)一個(gè)顯著的伸長開始出現(xiàn)，而拉力的增加并不明顯。這就是眾所周知的材料的屈服現(xiàn)象，B點(diǎn)的應(yīng)力被稱為屈服點(diǎn)或者屈服應(yīng)力。在區(qū)域BC中，材料被認(rèn)為是塑性的，事實(shí)上桿的塑性伸長是達(dá)到比例極限時(shí)伸長的10到15倍

24、。,.,12,At point C the material begins to strain harden and to offer additional resistance to increase in load. Thus, with further elongation the stress increases, and it reaches its maximum value, or ultimate stress, at point D. Beyond this point further stretching of the bar is accompanied by a red

25、uction in the load, and fracture of the specimen finally occurs at point E on the diagram.,材料在C點(diǎn)出現(xiàn)應(yīng)變強(qiáng)化，對(duì)載荷的增加產(chǎn)生了額外的阻力。這樣，隨著進(jìn)一步的伸長，應(yīng)力隨之增加，直到D點(diǎn)，應(yīng)力達(dá)到最大值即極限應(yīng)力。超過D點(diǎn)以后，進(jìn)一步的伸長伴隨著載荷的減少，最后在圖表的E點(diǎn)處，樣品發(fā)生斷裂。,.,13,During elongation of the bar a lateral contraction occurs, resulting in a decrease in the cross-sect

26、ional area of the bar. This phenomenon has no effect on the stress-strain diagram up to about point C, but beyond that point the decease in area will have a noticeable effect upon the calculated value of stress. A pronounced necking of the bar occurs (see Fig.2), and if the actual cross-sectional ar

27、ea at the narrow part of the neck is used in calculating , it will be found that the true stress-strain curve follows the dashed line CE. Whereas the total load the bar can carry does indeed diminish after the ultimate stress is reached (line DE), this reduction is due to the decrease in area and no

28、t to a loss in strength of the material itself.,在伸長過程中，圓棒發(fā)生了一個(gè)橫向的收縮，導(dǎo)致了圓棒橫截面積的減少。直到C點(diǎn)為止，這個(gè)現(xiàn)象對(duì)應(yīng)力-應(yīng)變圖都沒有影響，但是超出C點(diǎn)以后，面積的減少對(duì)應(yīng)力的計(jì)算有著顯著的影響。圓棒發(fā)生了一個(gè)明顯的頸縮(見圖2)，如果在計(jì)算時(shí)使用頸縮處狹窄的真實(shí)橫截面積，我們發(fā)現(xiàn)真實(shí)應(yīng)力-應(yīng)變曲線將沿著虛線CE進(jìn)行。然而，當(dāng)達(dá)到極限應(yīng)力時(shí)(線段DE)，圓棒的總載荷可能真正的減少，這個(gè)減少歸功于面積的減少而不是材料本身強(qiáng)度的損失。,.,14,The material actually withstands an increa

29、se in stress up to the point of failure. For most practical purposes, however, the conventional stress-strain curve OABCDE, based upon the original cross-sectional area of the specimen, provides satisfactory information for design purposes.,直到失效點(diǎn)為止，材料一直承受應(yīng)力的增加。然而，對(duì)大多數(shù)實(shí)際目的而言，建立在樣品的原始橫截面積上的傳統(tǒng)應(yīng)力-應(yīng)變曲線OA

30、BCDE給設(shè)計(jì)用途提供了令人滿意的信息。,.,15,The diagram in Fig.1 has been drawn to show the general characteristics of the stress-strain curve. There is an initial region on the stress-strain curve in which the material behaves both elastically and linearly. The region from O to A on the stress-strain diagram for ste

31、el is an example. The presence of a pronounced yield point followed by large plastic strains is somewhat unique to steel, which is the most common structural metal in use today. Aluminium alloys exhibit a more gradual transition from the linear to the nonlinear region.,圖1顯示了應(yīng)力-應(yīng)變曲線的一般特征，在這個(gè)曲線上有一個(gè)體現(xiàn)材

32、料的彈性和線性的初始區(qū)域。鋼的應(yīng)力-應(yīng)變曲線上從O點(diǎn)到A點(diǎn)的這個(gè)區(qū)域就是一個(gè)例子。緊隨大塑性應(yīng)變之后的顯著的屈服點(diǎn)現(xiàn)象是目前最常用的結(jié)構(gòu)金屬鋼的一點(diǎn)獨(dú)特的性質(zhì)。鋁合金則展示出了從線性到非線性區(qū)域的更平緩的轉(zhuǎn)變。,.,16,Both steel and many aluminium alloys will undergo large strain before failure and are therefore classified as ductile. On the other hand, materials that are brittle fail at relatively low v

33、alues of strain. Examples include ceramics, cast iron, concrete, certain metallic alloys, and glass.,鋼和許多鋁合金在失效之前都會(huì)出現(xiàn)大的應(yīng)變，因此可以被分類為韌性材料。另一方面，許多材料在相當(dāng)小的應(yīng)變時(shí)也會(huì)出現(xiàn)破裂失效，例如陶瓷，鑄鐵，混凝土，某些金屬合金和玻璃。,.,17,Translation When a structure is subjected to dynamic loading, the whole or part of it is accelerated with the r

34、esult that inertia forces are introduced. Due to the influence of inertia forces, the stresses vary during and after loading so that a particular state of stress exists only at a corresponding instant during the process. In many cases, however, when the loads are gradually applied or change slowly,

35、the dynamic effect is insignificant and can be neglected. With suddenly applied loads the effect of inertia forces must be taken into account and in extreme cases such as impact or resonance vibration, the dynamic effect predominates.,當(dāng)一個(gè)結(jié)構(gòu)被施加動(dòng)載荷時(shí)，它的整體或者部分會(huì)由于慣性力的引入而被加速。由于慣性力的影響，在加載過程中和加載后的應(yīng)力變化很大，以至于

36、在過程中每一個(gè)瞬間只對(duì)應(yīng)一個(gè)特別的應(yīng)力狀態(tài)。然而，在許多情況下，當(dāng)載荷是緩慢增加或者變化很小時(shí)，動(dòng)態(tài)影響是無關(guān)緊要的或者是可以被忽略的。但是在突然加載時(shí)，慣性力的影響必須被考慮，而且在一些特殊的情況下例如沖擊或者共振時(shí)，動(dòng)態(tài)作用是主要的影響因素。,.,18,As mentioned previously, the dynamic effect, i.e., the influence of inertia forces on the process of stress development in a body, depends on the dynamic loading condition

37、s. Three groups of typical phenomena can be distinguished. There are (1) quasi-static states of stress, (2) vibrations, and (3) stress waves. The limits between these groups are not clearly defined, however, and frequently the phenomena associated with more than one groups can occur in the same dyna

38、mic event.,正如前面所提到的一樣，動(dòng)力學(xué)的影響也就是在一個(gè)物體中，根據(jù)動(dòng)態(tài)加載的條件，慣性力對(duì)應(yīng)力發(fā)展過程的影響。這些影響可以區(qū)分為三種典型的現(xiàn)象。它們是應(yīng)力的準(zhǔn)靜態(tài)狀態(tài)， 振動(dòng)和應(yīng)力波。然而，三種現(xiàn)象的界限并沒有被清楚的說明，因此常常在同一個(gè)動(dòng)力學(xué)事件中有超過一種以上的現(xiàn)象發(fā)生。,.,19,The dynamic response of a body depends not only on the magnitude of the forces acting but also, to a decisive extent, on their rate of change. Thus,

39、 while stress waves are produced by the change of forces, the frequency of these waves is determined by their rate of change. If the change of forces is due to the impact of a striking body, this means that the response of the body struck depends on the time of contact between the two bodies.,一個(gè)物體的動(dòng)

40、態(tài)響應(yīng)不但跟作用力的數(shù)值有關(guān)，起決定因素的還是這些力變化的頻率。因此，當(dāng)力的變化產(chǎn)生應(yīng)力波時(shí)，這些波的頻率已經(jīng)由產(chǎn)生它們的力的變化率所確定了。如果這些力的變化是由于一個(gè)物體的沖擊，那就意味著這個(gè)被撞擊物體的響應(yīng)決定于這兩個(gè)物體的接觸時(shí)間。,.,20,When the forces acting on a body change slowly so that the frequency is very low, the length of the wave is usually great compared with the dimensions of the body. In such ext

41、reme cases, the stress distribution is independent of the rate of the forces. Although the stresses vary in magnitude during the process, their distribution remains the same throughout and is identical with that under corresponding static loading. The external forces acting on the body are in equili

42、brium throughout the event and all stresses vanish when these forces cease to act. Problems in which the behavior follows this pattern are called quasi-static.,當(dāng)作用在物體上的力變化很慢導(dǎo)致頻率很低時(shí)，波長通常要大于物體本身的尺寸。在這樣極端的情況下，應(yīng)力的分布與力的變化率無關(guān)。盡管在加載過程中，應(yīng)力大小有變化，但是在整個(gè)過程中它們的分布和在相應(yīng)靜載荷作用下的情況相同。作用在物體上的外力在過程中保持均衡，而且當(dāng)外力停止作用時(shí)，應(yīng)力消失。

43、我們把變化過程遵循上述形式的問題稱為準(zhǔn)靜態(tài)問題。,.,21,When the frequency of the loading cycle is of the same order as the resonance frequency of the body, the stress waves and their reflections cause vibrations, e.g., longitudinal or flexural vibrations. Due to inertia forces the stress distribution will differ to some ext

44、ent from that in comparable static or quasi-static cases and the external forces are not in equilibrium throughout the event.,當(dāng)循環(huán)加載的頻率與物體本身的共振頻率一致時(shí)，應(yīng)力波和它們的反射波可以引起振動(dòng)，例如，縱向的或者橫向的振動(dòng)。由于慣性力的存在，應(yīng)力的分布在一定程度上不同于靜態(tài)或者準(zhǔn)靜態(tài)的情況，外力在加載過程中也不是均衡的。,.,22,If the rate of change of the forces acting on a body corresponds w

45、ith a high frequency, i.e., with the generation of waves which are short compared with the dimensions of the body, the effect of stress waves predominates. In such cases the stress distribution differs greatly from that produced under static or quasi-static conditions.,如果作用在物體上的外力的變化率，對(duì)應(yīng)于一個(gè)高的頻率，也就是說

46、，產(chǎn)生的波長小于物體本身的尺寸時(shí)，那么應(yīng)力波的效果就很明顯。在這樣的情況下，應(yīng)力的分布在很大程度上不同于在靜態(tài)或者準(zhǔn)靜態(tài)條件下的分布。,.,23,一個(gè)經(jīng)常遇到的問題是，在動(dòng)態(tài)條件下，包括帶有一個(gè)缺口或者別的不規(guī)則形狀的物體的應(yīng)力波或者振動(dòng)，應(yīng)力集中因子的確定。在這樣的情況下，問題的解決方法取決于波長和缺口的相關(guān)尺寸。如果缺口的尺寸小于波長，那么在缺口附近應(yīng)力的分布類似于相對(duì)應(yīng)靜載下的分布。因此，這樣加載在物體相應(yīng)的一小部分的模型上也會(huì)產(chǎn)生同樣的應(yīng)力分布。,A problem frequently encountered is that of determining the stress con

47、centration factor under dynamic conditions involving stress waves or vibrations at a notch or other irregularity in the shape of a body. In such cases the procedure to be adopted depends on the relative dimensions of the wavelength and the notch. If the dimensions of the notch are small compared wit

48、h the wavelength, the stress distribution in the neighborhood of the notch will be similar to that under comparable static loading. Such loading applied to a model of the relevant small part of the body will therefore produce the same stress distribution.,.,24,When the length of a stress wave is of

49、the same order or smaller than the dimensions of a body or, for instance, of a notch in it, dynamic methods must be applied. This is also true in the case of vibrations. Since the stress concentration factor depends on the length of the stress wave involved, it is obvious that there is no generally

50、applicable dynamic factor of stress concentration.,當(dāng)一個(gè)應(yīng)力波的波長等于或者小于一個(gè)物體的本身尺寸，或者具體來說它等于或者小于物體上的一個(gè)缺口的尺寸時(shí)候，我們必須采用動(dòng)力學(xué)方法。在振動(dòng)情況下，同樣如此。由于應(yīng)力集中因子與應(yīng)力波本身的波長有關(guān)，因此很明顯，沒有普遍適用的應(yīng)力集中動(dòng)態(tài)因子。,.,25,The modern digital computer can be defined as an electronic device for high speed automatic information processing. This powe

51、rful computational device can receive the information provided by the user, operate upon it, and produce new information. For a better understanding of this process of acquisition, processing, and delivering of information, we should identify the basic components of a computer, and analyze their fun

52、ctions. These components are shown in Fig.1 in a schematic manner.,現(xiàn)代數(shù)字計(jì)算機(jī)可以被定義為一臺(tái)自動(dòng)高速處理信息的電子裝置。這個(gè)功能強(qiáng)大的計(jì)算裝置可以接收用戶提供的信息，并對(duì)它進(jìn)行處理，然后產(chǎn)生新的信息。為了更好的了解信息的獲得、處理以及傳遞的過程，我們應(yīng)該了解一臺(tái)計(jì)算機(jī)的基本組成，并且分析它們的功能。這些組成顯示在示意圖1中。,Translation,.,26,The information supplied by the user is received by the input unit or reader. The u

53、ser does not give that information in a completely arbitrary manner, but will have to follow some specific rules, to allow for its interpretation. The physical media used to register information is known as information support. Examples of common information support are punched cards, punched paper

54、tapes, magnetic disks, etc. For each type of information support there is a type of input unit which can assimilate it.,用戶提供的信息通過輸入單元或者讀取設(shè)備來接收。但是考慮到它的編譯方式，用戶不能用完全任意的形式提供信息，而是必須要遵從一些特殊的規(guī)則。用來記錄信息的物理介質(zhì)被稱為信息載體。常用的信息載體有打孔卡片，打孔紙帶，磁盤等等。對(duì)于每一類信息載體來說，都有一種與之對(duì)應(yīng)用來接收信息的輸入單元。,.,27,The user supplied the computer wi

55、th information which is composed of data and instructions. The set of instructions given to the computer, defining the operations required to achieve the solution is known as a program or computer program. Program and data are not, in general, read simultaneously or intermixed. The program is normal

56、ly read first. Then the computer operates according to the instructions included in the program which indicates to the computer when and how to read the data. This process is normally called execution or processing of the program.,用戶提供給計(jì)算機(jī)由數(shù)據(jù)和指令組成的信息。這套給計(jì)算機(jī)的指令，定義了解決問題的必要操作，也就是眾所周知的程序或者計(jì)算機(jī)程序。一般來說，程序和

57、數(shù)據(jù)不是同時(shí)或者混和讀取的。通常程序先被讀取，然后計(jì)算機(jī)依照被包含在程序中指示該何時(shí)以及如何讀數(shù)據(jù)的指令進(jìn)行操作。 這個(gè)過程通常被稱為執(zhí)行或者處理程序。,.,28,The information which enters the computer is immediately transferred to the computer memory. A computer can have several memories, including a primary memory, which will always exist, and one or more secondary memories

58、, which may or may not exist. The function of a memory is to store information for short or long periods of time. The primary memory can be considered as to heat of the computer, since all the information that it receives or generates, must pass through the primary memory.,輸入計(jì)算機(jī)的信息立刻被傳遞到計(jì)算機(jī)的存儲(chǔ)器里。一臺(tái)計(jì)

59、算機(jī)可能有幾個(gè)存儲(chǔ)器，包括一個(gè)總是存在的主存儲(chǔ)器和一個(gè)或者多個(gè)可能存在也可能不存在的二級(jí)存儲(chǔ)器。存儲(chǔ)器的功能是短期或者長期儲(chǔ)存信息。由于計(jì)算機(jī)接收或者產(chǎn)生的所有信息都必須通過主存儲(chǔ)器，所以主存儲(chǔ)器被認(rèn)為是計(jì)算機(jī)的“心臟”。,.,29,The primary memory can be conceived as a large collection of small cells which are normally called memory positions. Each memory position is identified by a number, called memory address. The information read or generated by the computer is subdivided into information units, called words. A word is further subdivided into characters. The number of characters in a word defines the word length. The content of a memory position is a word, which can be put into or taken from th