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] 总线不仅仅是一组线缆，它还包括一些逻辑电路。此处是一种形象说法，有关总线的概念请见本章1. 6节。
[2] 因为没有给出总线宽度，故每次传送可以理解为每秒钟或每分钟所传送的字节数、字数等。
KEYWORDS
computer 计算机 input device 输入设备
information processing 信息处理 output device 输出设备
hardware 硬件 main memory 主存储器
software 软件 central processing unit(CPU)中央处理器
program 程序 bus 总线
general-purpose machine 通用(计算)机 microcomputer 微型计算机
special-purpose machine 专用(计算)机 minicomputer 小型计算机
instruction 指令 mainframe 主机，特大型机
set of instruction 指令集，指令系统
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
翻译:
【例】假设在总线上从一个部件向另一个部件传送某个信息需要4. 5微秒，也写成4.5 s。
(a)传送需要多少秒钟?
(b)1分钟能传送多少次?
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分钟有60秒，所以传送次数是60s/0.000 004 5s，即13 300 000。请注意，由于原始数只有两位有效值，所以结果也不应超过两位或三位有效数。
表1-1表明在量度系统中，词头kilo为1000， mega为1 000 000。但在计算机科学中， kilo为210 或1024。1000与1024之间的误差不到3%，因而可以认为计算机科学中kilo大约为1000，虽然它稍小一些。对于mega和giga的情形也是如此，如表1-2所示。这时，近似程度稍差一些，但对mega而言，仍在5%以内。
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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