Example Suppose it takes 4. 5 microseconds，also written 4. 5 s，to transfer some information across the bus from one component to another. (a)How many seconds are required for the transfer?(b)How many transfers can take place during one minute?[2]

　　(a)A time of 4. 5 s is 4. 5 × 10-6 from Table 1-1 or 0. 000 0045 s.(b)Because there

　　are 60 seconds in one minute，the number of times the transfer can occur is(60 s)/(0. 000 004 5 s/transfer)or 13 300 000 transfers. Note that since the original value was given with two significant figures，the result should not be given to more than two or three significant figures.

　　Table 1-1 shows that in the metric system the prefix kilo-is 1 000 and mega-is 1 000 000. But in computer science，a kilo-is 210 or 1024.The different between 1 000 and 1 024 is less than 3%，so you can think of a computer science kilo-as being about 1 000 even though it is a little more. The same applies to mega-and giga-，as in Table 1-2. This time，the approximation is a little worse，but for mega-it is still within 5%.

　　Table 1-2 Computer science values of the large prefixes

　　Prefix Computer science value

　　giga- 230 = 1 073 741 824

　　mega- 220 = 1 048 576

　　kilo- 210 = 1 024

　　NOTES

　　[1] 總線不僅僅是一組線纜，它還包括一些邏輯電路。此處是一種形象說(shuō)法，有關(guān)總線的概念請(qǐng)見本章1. 6節(jié)。

　　[2] 因?yàn)闆]有給出總線寬度，故每次傳送可以理解為每秒鐘或每分鐘所傳送的字節(jié)數(shù)、字?jǐn)?shù)等。

　　KEYWORDS

　　computer 計(jì)算機(jī) input device 輸入設(shè)備

　　information processing 信息處理 output device 輸出設(shè)備

　　hardware 硬件 main memory 主存儲(chǔ)器

　　software 軟件 central processing unit(CPU)中央處理器

　　program 程序 bus 總線

　　general-purpose machine 通用(計(jì)算)機(jī) microcomputer 微型計(jì)算機(jī)

　　special-purpose machine 專用(計(jì)算)機(jī) minicomputer 小型計(jì)算機(jī)

　　instruction 指令 mainframe 主機(jī)，特大型機(jī)

　　set of instruction 指令集，指令系統(tǒng)

　　EXERCISES

　　1. Multiple choices.

　　(1)When we store a problem into a computer， is necessary.

　　a. space b. time

　　c. input device d. output device

　　(2)Early computer solved problems.

　　a. control b. business applications

　　c. engineering d. mathematical

　　(3)We can use prefix micro to express .

　　a. time metric b. space metric

　　c. both time and space metrics d. 10-6

　　(4)We can say a bus is simply .

　　a. a group of wires b. a wire

　　c. a 8-bit bus d. a 16-bit bus

　　(5)A computer system user generally more cares for .

　　a. physical size of the computer

　　b. storage size

　　c. speed of computation

　　d. efficiency of the computer

　　(6)According to the physical size of computers we can classify the computers into

　　.

　　a. microcomputer b. minicomputer

　　c. mainframe d. supercomputer

　　(7)Prefix“mega”used for computer science is .

　　a. larger than 106 b. smaller than 106

　　c. equal to 220 d. 1 048 576

　　(8)The basic hardware components of any computer include .

　　a. CPU b. main memory

　　c. input devices d. output devices

　　2. Fill in the blank with appropriate words or phrases found behind this exercise.

　　(1)A computer system solves a problem by .

　　(2)The amount of effective work of a computer can be indicated by directly. (3)Computer systems consist of .

　　(4)Computer that can solve only one kind of problem is a .

　　(5)Computer that can solve many different kinds of problems is a .

　　(6) instruct the hardware.

　　(7) is difficult and expensive to change.

　　(8)We usually show the computer components in a .

　　a. general-purpose machine

　　b. hardware

　　c. accepting input，processing problem，and producing output

　　d. block diagram

　　e. software

　　f. storage size

　　g. special-purpose machine

　　h. hardware and software

　　翻譯:

　　【例】假設(shè)在總線上從一個(gè)部件向另一個(gè)部件傳送某個(gè)信息需要4. 5微秒，也寫成4.5 s。

　　(a)傳送需要多少秒鐘?

　　(b)1分鐘能傳送多少次?

　　解：(a)如表1-1所示，4. 5 s是4. 5× 10-6s，即0. 000 004 5秒;

　　(b)由于1分鐘有60秒，所以傳送次數(shù)是60s/0.000 004 5s，即13 300 000。請(qǐng)注意，由于原始數(shù)只有兩位有效值，所以結(jié)果也不應(yīng)超過兩位或三位有效數(shù)。

　　表1-1表明在量度系統(tǒng)中，詞頭kilo為1000， mega為1 000 000。但在計(jì)算機(jī)科學(xué)中， kilo為210 或1024。1000與1024之間的誤差不到3%，因而可以認(rèn)為計(jì)算機(jī)科學(xué)中kilo大約為1000，雖然它稍小一些。對(duì)于mega和giga的情形也是如此，如表1-2所示。這時(shí)，近似程度稍差一些，但對(duì)mega而言，仍在5%以內(nèi)。

　　答案:

　　1.(1)a，c

　　(2)c，d

　　(3)a，d

　　(4)a，c，d

　　(5)b，c，d

　　(6)a，b，c，d

　　(7)c，d

　　(8)a，b，c，d

　　2.(1)c

　　(2)f

　　(3)h

　　(4)g

　　(5)a

　　(6)e

　　(7)b

　　(8)d

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