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。此處是一種形象說法,有關(guān)總線的概念請見本章1. 6節(jié)。
[2] 因為沒有給出總線寬度,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(計算)機(jī) microcomputer 微型計算機(jī)
special-purpose machine 專用(計算)機(jī) minicomputer 小型計算機(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)在總線上從一個部件向另一個部件傳送某個信息需要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)為計算機(jī)科學(xué)中kilo大約為1000,雖然它稍小一些。對于mega和giga的情形也是如此,如表1-2所示。這時,近似程度稍差一些,但對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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