1. COMPUTER SCIENCE
AN OVERVIEW

2. Q & A

3. Question: What can I do if I can’t understand the text?

4. College is quite different from high school, you have to learn by yourself ! Do not rely on teachers!
Learning method:
Look up the new words in the dictionary;
Use the library;
Discuss with other students;
Use the reference books;
Search related knowledge online.

7. Question: Are we learning English or Computer Science?

8. We learn both. But computer technology is more important!

9. Class Review

10. The Study of Algorithms
An algorithm is a set of steps that defines how a task is performed.
In the domain of computing machinery, algorithms are represented as programs within computers.

11. The Role of Abstraction
Abstraction - the distinction between the external properties of a component and the internal details of the component’s construction.
It is abstraction that allows us to ignore the internal details of a complex device and use it as a single, comprehensible unit.

12. Figure 0.6: The hierarchy of abstraction in the hardware of a typical personal computer

13. Vocabulary

14. Part I:
Machine Architecture

15. A major process in the development of a science is the construction of theories that are confirmed or rejected by experimentation.
In some cases these theories lie dormant for extended periods, waiting for technology to develop to the point that they can be tested.

16. Ch. 1 Data Storage Storage of bits. First class Main memory.
Mass storage.
Coding information for storage.
The binary system.
Storing integers.
Storing Fractions.
Communication errors.
First class
Second class

17. 1.1 Bits and Their Storage Bit (binary digit ):
is either one of two digits : 0 or 1
Here 0 or 1 is just a symbol
Unnecessarily has digital meaning

18. Boolean Operations AND (与） P AND Q both P and Q
P is a statement, and Q is other a statement, each has value True or False,
represented by 1, and 0 respectively .

19. Boolean Operations
OR P OR Q
at least one of P and Q is True
XOR P XOR Q
at least one of P and Q is True
But not both

20. Figure 1.1: The Boolean operations AND, OR, and XOR (exclusive or)

21. Gates are devices that produce the output of a Boolean operation when given the operation’s input values.
A flip-flop is a circuit that has one of two output values (i.e., 0 or 1), the output will flip or flop between two values under control of external stimuli.
A flip-flop is ideal for the storage of a bit within a computer (on a single wafer or chip). A flip-flop loses data when its power is turned off.

22. Figure 1.2: A pictorial representation of AND, OR, XOR, and NOT gates as well as their input and output values (continued)
copy to blackboard

23. Figure 1.2: A pictorial representation of AND, OR, XOR, and NOT gates as well as their input and output values

24. Figure 1.3: A simple flip-flop circuit

25. Figure 1.4: Setting the output of a flip-flop to 1 (continued)1

26. Figure 1.4: Setting the output of a flip-flop to 1 (continued)

27. Figure 1.4: Setting the output of a flip-flop to 1

28. Temporarily placing the value 1 on the lower input1

29. This output will persist after the input value returns to 01 1

30. A flip-flop is a circuit that produces an output value of 0 or 1 that remains constant until a temporary pulse from another circuit causes it to shift to the other value.

31. The significance of a flip-flop is that it is ideal for the storage of a bit within a computer. The value stored in it is the output value of the flip-flop. Other circuits can easily adjust this value by sending pulses to the flip-flop’s inputs.

32. Figure 1.5: Another way of constructing a flip-flop
First study it by yourself!

33. Figure 1.5: Another way of constructing a flip-flop1 1

34. Figure 1.5: Another way of constructing a flip-flop1 1 1 1

35. Representing Numeric Value
anBn+a(n-1)  Bn-1+…+a1 B1 +a0 B0
B is called base
n is called position quantity
an is called digit

36. （101）10=1 × 102＋0×101＋1×100
（101）2＝1×22＋0×21＋1×20 ＝ （5）10
（101）16＝1×162＋0×161＋1×160 ＝（257）10

37. The hexadecimal coding system
It is used to simplify the representation of long bit patterns of a stream. It takes advantage of the fact that bit patterns within a machine tend to have lengths in multiples of four.

38. Figure 1.6: The hexadecimal coding system
There’s a mistake in our textbook
(10)10=(A)16
(11)10=(B)16
(12)10=(C)16
(13)10=(D)16
(14)10=(E)16
(15)10=(F)16

39. The hexadecimal coding system
=>
A4C8 A 4 C 8
This is obtained by dividing the bit pattern into substrings of length four and then representing each substring by its hexadecimal equivalent.

40. 1.2 Main Memory Cells - a typical cell size is 8 or called byte.
A byte (B) consists of a grouping of eight binary digits ("bits"), and is typically considered the smallest addressable unit of data.
Address is used to identify individual cells in a main memory.

42. Random access memory (RAM)(随机存储器 ).
Read only memory (ROM)(只读存储器 ).
Most significant bit (MSB) and least significant bit (LSB).

43. If you want a larger playing field in real life, you have to add onto the field by acquiring more property. With RAM, you do this by adding additional memory. In most cases, this memory comes in the form of "RAM sticks," small rectangular cards studded with memory modules.

45. ROM is a type of unchangeable memory residing in chips on your mother board. ROM contains the bare minimum of instructions needed to start your computer. Because it's used for critical functions, it can't be removed short of ripping it out of the motherboard; adding to it is just as difficult.
Incidentally, the term "ROM" is also used, not entirely correctly, when referring to some kinds of storage media, that can't be modified, such as CD-ROMs.

46. Figure 1.7: The organization of a byte-size memory cell

47. Address is used to identify individual cells
in a main memory.

48. Figure 1.8: Memory cells arranged by address

49. 1.3 Mass Storage Secondary memory.
Storing large units of data (called files).
Mass storage systems are slow due to mechanical motion requirement.
On-line Vs. off-line operations.

50. Figure 1.9: Memory cells arranged by address
找一幅动画

51. Disk Device Terminology
Outer
Track
Inner
Arm
Head
Sector
Platter
Actuator
Several platters, with information recorded magnetically on both surfaces (usually)
Bits recorded in tracks, which in turn divided into sectors (e.g., 512 Bytes)
Actuator（致动器） moves head (end of arm,1/surface) over track (“seek”), select surface, wait for sector rotate under head, then read or write
“Cylinder”: all tracks under heads

52. Figure 1.10: CD storage format
靠激光照射反射

53. Figure 1.11: A magnetic tape storage mechanism

54. Figure 1.12: Logical records versus physical records on a disk

55. Seek Time :
the time required to move the read/write head from one track to another;
Rotation Delay: ( latency time )
half the time required for the disk to make a complete rotation.which is the average amount of time required for the desired data to rotate around to the r/w head once the head has been positioned over the rotated track.

56. Access Time
the sum of seek time and rotation delay.
Transfer Rate :
the rate at which data can be transferred to or from the disk.

57. 1.4 Representing Information as Bit Patterns
Representing Text
By means of code in which each of the symbols in the text is assigned a unique bit pattern.

58. Text Coding System
American Standard Code for Information Interchange (ASCII) - 8-bit codes.-APPENDIX A
International Standards Organization (ISO) - 16-bit codes. ( Unicode )
32-bit code

59. Figure 1.13: The message “Hello.” in ASCII

60. A practice:

61. Representing Numeric Value
Binary-decimal number conversion
Numeric Value :
anBn+a(n-1)  Bn-1+…+a1 B1 +a0 B0
B is called base
n is called position quantity
an is called digit

62. Figure 1.14: The base ten and binary systems

63. Figure 1.15: Decoding the binary representation 100101

65. Figure 1.16: An algorithm for finding the binary representation of a positive integer

66. Figure 1. 17: Applying the algorithm in Figure 1
Figure 1.17: Applying the algorithm in Figure 1.15 to obtain the binary representation of thirteen

67. Class practice：
Convert the following base ten representation to its equivalent binary form: 27

68. Representing Images

69. Representing Images – Two ways
I) Bit maps representation - Tag Image
An image is considered as to be a collection of dots ,each of which is called a pixel，short for “ picture element”
In its simple form, an image is represented as a long string of bits representing the rows of pixels in the image, where each bit is either 1 or 0 depending on whether the corresponding pixel in image is black or white.

70. II) Vector Representing
Each image is represented as a collection of lines and curves .Such description leaves the detail of how the lines and curves are drawn to the device.

71. Three-byte-per-pixel (P40)
Image types:
Format File (TIFF),
Graphic Interchange Format (GIF),
Joint Photographs Experts Group (JPEG).

72. Representing Sound
The most generic method of encoding audio information for computer storage and manipulation is to sample the amplitudeof the sound wave at regular intervals and record the series of values obtained.

73. Figure 1. 18: The sound wave represented by the sequence 0, 1. 5, 2

74. Homework
P26 1,4,5,6,7
P29 1,2,3
P42 5,6,7,8,10

75. Rules Copy the questions Write in neat words Hand in on next class
If you don’t know the answer, try some research.

76. Vocabulary

77. COMPUTER SCIENCE
AN OVERVIEW

78. Vocabulary

79. Q & A

80. I feel the contents are very discrete, I don’t know how to grasp them.

81. Your advice is welcomed!
We are doing an overview, we have to deal with almost all topics in computer science.
I will try to connect them as close as I can.
Your advice is welcomed!

82. Class Review

83. Bits and Their Storage Bit (binary digit ):
is either one of two digits : 0 or 1
Here 0 or 1 is just a symbol
Unnecessarily has digital meaning

84. Figure 1.1: The Boolean operations AND, OR, and XOR (exclusive or)

85. Figure 1.2: A pictorial representation of AND, OR, XOR, and NOT gates as well as their input and output values (continued)
用抽象的符号来表示这些运算电路

86. Figure 1.2: A pictorial representation of AND, OR, XOR, and NOT gates as well as their input and output values

87. Figure 1.3: A simple flip-flop circuit
计算机里面存储0，1
A flip-flop is a circuit that produces an output value of 0 or 1 that remains constant until a temporary pulse from another circuit causes it to shift to the other value.

88. Representing Numeric Value
anBn+a(n-1)  Bn-1+…+a1 B1 +a0 B0
B is called base
n is called position quantity
an is called digit

89. （101）10=1 × 102＋0×101＋1×100
（101）2＝1×22＋0×21＋1×20 ＝ （5）10
（101）16＝1×162＋0×161＋1×160 ＝（257）10

90. Figure 1.6: The hexadecimal coding system
多位存储的简化表示

91. The hexadecimal coding system
=>
A4C8 A 4 C 8
This is obtained by dividing the bit pattern into substrings of length four and then representing each substring by its hexadecimal equivalent.

92. Main Memory Storage Type
Cell- a typical cell size is 8 or called byte.
A byte (B) consists of a grouping of eight binary digits ("bits"), and is typically considered the smallest addressable unit of data.
Address is used to identify individual cells in a main memory.
计算机里面怎么存储

93. Figure 1.8: Memory cells arranged by address

94. Figure 1.7: The organization of a byte-size memory cell

95. Measuring Memory Capacity
1 Byte ＝ 8 Bit
1 KB（kilobyte）＝ 1024 (which is 210)Byte
1 MB（megabyte）＝ 1024 KB
1 GB（gigabyte）＝ 1024 MB
1 TB（terabyte）＝ 1024 GB

96. Main Memory Random access memory (RAM) Read only memory (ROM)
Most significant bit (MSB) and least significant bit (LSB).
存储在哪里

97. Mass Storage Secondary memory.
Storing large units of data (called files).
Mass storage systems are slow due to mechanical motion requirement.
On-line Vs. off-line operations.

98. What’s Inside A Disk Drive?

99. 1.4 Representing Information as Bit Patterns
Representing Text
Representing Image
Representing Sound

100. Representing Text in ASCII

101. Representing Images
Bit maps representation
Vector Representing

102. Representing Sound

103. 1.5 Binary System Binary addition. Fractions in binary.
Radix point (same as decimal point in decimal notation).

104. （101）10=1 × 102＋0×101＋1×100
（101）2＝1×22＋0×21＋1×20 ＝ （5）10
（101）16＝1×162＋0×161＋1×160 ＝（257）10

105. Figure 1.19: The binary addition facts

106. Practice:

107. Fractions in Binary
Radix point (same as decimal point in decimal notation).

108. Figure 1.20: Decoding the binary representation 101.101
黑板画图表示

110. Practice:
Convert the following binary representation to its equivalent base ten form:

111. Transform the fraction 0.875 to binary
Example
Transform the fraction to binary
Solution
Write the fraction at the left corner. Multiply the number continuously by 2 and extract the integer part as the binary digit. Stop when the number is 0.0.
    0.0

112. Transform the fraction 0.4 to a binary of 6 bits.
Example
Transform the fraction 0.4 to a binary of 6 bits.
Solution
Write the fraction at the left corner. Multiply the number continuously by 2 and extract the integer part as the binary digit. You can never get the exact binary representation. Stop when you have 6 bits.
0.4       1.6

113. 1.6 Storing Integers Excess notation Two’s complement notation
Addition in two’s complement notation.
Overflow problem.
Memory size Vs. accuracy of number representation.

114. Two’s Complement Notation
In two’s complement system , there is a convenient relationship between the patterns representing positive and negative values of the same magnitude.
They are identical when read from right to left up to and including the first 1.From then on,the patterns are complements of one another.

115. Figure 1.21: Two’s complement notation systems

116. Figure 1. 22: Coding the value -6 in two’s
Figure 1.22: Coding the value -6 in two’s complement notation using four bits

117. Representing negative numbers in two’s complement

118. Class practice
Convert the base ten form －16 to two‘s complement representation using patterns of length eight.
First, we convert its positive part to binary form using patterns of length eight.
Second, we have two ways:
1) invert each bit and add 1.
2) copy the bits from right to left until a 1 has been copied and invert the remaining bits.

119. Class practice
Convert the two's complement representation to its equivalent base ten form.
First, we get that it’s a negative value.
Second, we try to find it’s positive counterpart.

120. Figure 1.23: Addition problems converted to two’s complement notation

121. Summary of Two’s Complement

123. Example of Overflow：
5＋4： 0101＋0100 ＝ 1001
The hospital example (P49)

124. Note that the difference between an excess system and a two’s complement system is that the sign bits are reversed.
What’s the difference between an excess system and a two’s complement system?

125. Figure 1.24: An excess eight conversion table

127. Figure 1. 25: An excess notation system using bit
Figure 1.25: An excess notation system using bit patterns of length three

128. 1.7 Storing Fractions

129. 1.7 Storing Fractions Floating Point Notation Exponent Field
Mantissa Field

130. Figure 1.26: Floating-point notation components

131. Example:
Suppose one byte contains bit pattern , we get mantissa 1011,and put radix point on its left side ,then we obtain
The exponent field is 110,it means 2 (three bit excess method ),so, we move radix point two places to right,and get result It is 2 ¾.

132. Attention: ( Normalized Form )
When we fill the mantissa field , the rule is to copy the bit pattern appearing in the binary representation from left to right ,starting with the leftmost 1.
Storing 3/8, which is .011 in binary notation, in this case ,the mantissa will be 1100, it will not be 0110

133. Class practice Convert the following value into floating-point format:
23/4
First get its binary representation, both its integer part and fraction part.
Second, when we fill the mantissa field , copy the bit pattern appearing in the binary representation from left to right ,starting with the leftmost 1.
Answer:
Third, use three bit excess method to get the exponent field(+2).

134. Truncation Errors
also called Round off Error
1. use longer mantissa field
(usually, 32bits are used to store floating point value )
2. Non-terminating expansion, like to express 1/3 in decimal point notation

135. Figure 1.27: Coding the value 2 5/8

136. Q & A

137. Question 1: When I’m given a string of binary numbers, how do I know it’s in what notation?

138. Question2: When are these different notations are used?

139. Question 3: I still don’t understand the conversion between base ten form and floating-point notation.

140. Question 4 about the content in page 55

141. Class Review

142. Practice
Decode the following bit pattern using the floating-point format.

143. Practice Encode the following values into the floating-point format.
-31/2

144. 1.8 Data Compression
Run length encoding
Relative encoding
Frequency-dependent encoding
Variable length code Huffman code
Adaptive dictionary encoding
Lempel-Ziv encoding

145. Figure 1.28: Decompressing xyxxyzy (5, 4, x) using LZ77

146. 1.9 Communication Errors
How can you make sure the information you receive is correct???
Coding techniques for error detection and correction.
Parity bits.
Error-correcting codes.

147. Parity Bits
Odd parity
Even Parity
Checkbyte
Hamming Distance

148. Figure 1.29: The ASCII codes for the letters A and F adjusted for odd parity

149. Figure 1.30: An error-correcting code

150. Figure 1.31: Decoding the pattern 010100 using the code in Figure 1.30

151. Assignments: Page42 4, Page46 1，2，3，4, 5
Write down your student number on the cover.
Write down the steps.
Write down in neat words, with neat cover
Hand in your homework next Wednesday.
View the chapter review problems by yourself.

152. Q & A

153. Q1. I still don’t understand the Hamming Distance

154. Q2. Where’s the previous content stored in the cell number after exchanged with another one?

155. Q3. Can we have the vocabulary?

156. Q4. Why the other class is slower?

157. Related Readings
1.5
1.6
1.7 P52-P54
1.9 P62 Figure 1.29, Figure 1.30, Figure 1.31

158. The content you need to grasp:
A) Bits And Their Representation; Main Memory; Representing Information as Bit Patterns;
B) Storing Integer;；Storing Fractions;
C) Data Compression；The Binary System;