备份：AS 计算机课程术语及其解释

AS 计算机课程术语及其解释

AS computer science key terms and their explanations
说明

1. 本文列出了AS计算机学科中的术语及其解释，由选修AS计算机科目的全体学生共同写作完成。This document lists the terms used in AS computer science. The explanation of each term is given by the students who take the AS computer science subject.

2. 本文档为多人协作在线文档。严谨随意删除该文档中的内容。严禁恶意删除文档中的内容。违规者将被取消查阅该文档的权限。如果您对文档中的内容有疑问或者发现了错误，建议以批注的形式进行反馈。This document is an online collaborative editing document. You must NOT delete the contents of the document. Add comments on the content that you think is wrong or not good enough. You will be removed from the group of viewers if you delete some contents of this document deliberately.

3. 协作编写本文的目的是增加大家对计算机学科中术语的理解以及使用英文对其进行解释和描述的能力，进而提高在国际考试中应对解释性/描述性题目的能力，最终取得优异的成绩。The purpose of the document is to improve the understanding of terms of computer science and the ability to explain/describe the terms in English, eventually benefits all editors’ performance on the CIE examinations.

4. 编辑本文档时，请注意保持格式与全文格式保持一致。Keep the format and style consistent when you add/append contents to this document, so that it is readable.

5. 严禁在文档中输入任何和主题无关的内容，违反者将被取消查阅该文档的权限。Any contents that is not computer science related would be removed and the one who input the conent will be removed from the group.

6. 本着人人为我，我为人人的精神，管理员将根据大家对文档内容贡献的多少和贡献的质量周期性地进行考评。贡献排名靠前的将予以表扬并记录在校宝中；贡献很少的或者没有共贡献的同学将被取消查阅该文档的权限。 Everyone is encouraged to add/append terms and their explainations to this document. Those who contributes the most will be recorded in the SchoolPal system. Those who contributes nothing or ver few will be remove from the group of viewers.

7. 本文为多人协作完成，仅限于在对本文编辑做出共享的人群中进行分享。严禁私自拷贝并分享给非协作人员。This document is edited collaboratively and can ONLY shared with the group members. You must NOT copy this document and share it with others.

词条示例

1. Pixel
   1.1. a pixel is a basic element of a picture/bitmap.
   1.2. a pixel has a color.
   1.3. the color of a pixel consists of 3 primay colors: Red, Green and Blue .

2. Bitmap
   2.1. a bitmap is a image made up of pixels.
   2.2. the pixels are arranged as a matrix (in rows and columns).
   2.3. the number of columns times the number of rows is referred to as the resolution of the bitmap.
   2.4. the number of bits used to represent the color of each pixel is referred to as the color depth.
   2.5. Unscalable.

3. Denary numbers
   3.1. We count using a base-10 number systems
   3.2. Written using one of the symbols between 0 to 9 for each denary digit.

4. Binary numbers
   4.1. Written using one and zero.
   4.2. If we add 1 to a binary number, we get the number 1 higher than the number. Same as in other number systems.

5. Hexadecimal numbers
   5.1. Written using one of the symbols between 0 to 9 and A to F.
   5.2. A to F represents denary numbers 10 to 15.

6. Bits
   6.1. Digits in binary numbers.
   6.2. The abbreviation is ‘b’.

7. Nibbles
   7.1. A group of four bits in a unit.
   7.2. Two nibbles can be represented by two hexadecimal numbers.

8. Bytes
   8.1. A group of eight bits in a unit.
   8.2. The abbreviation is ‘B’.

9. Decimal prefix
   9.1. A kilobyte (kB) is 1000 bytes.
   9.2. A Megabyte (MB) is 1000 kilobytes.
   9.3. A Gigabyte (GB) is 1000 Megabytes.
   9.4. A Terabyte (TB) is 1000 Gigabytes.

10. Binary prefix
    10.1. A kibibyte (KiB) is 1024 bytes.
    10.2. A mebibyte (MiB) is 1024 kibibytes.
    10.3. A Gigibyte (GiB) is 1024 Mebibytes.
    10.4. A Tebibyte (TiB) is 1024 Gigibytes.

11. Signed integers
    11.1. Consisted of the binary numbers for the value with a bit to define the sign.
    11.2. The very first bit will be the sign instead of being the place value, which 0 to represent + and 1 to represent -.
    11.3. There are two other formats of signed integers, which is one’s complement and two’s complement.

12. One’s complement
    12.1. binary numbers obtained by subtracting each digit from 1.

13. Two’s complement
    13.1. The one’s complement of binary numbers, plus 1. 13.2. There is only one representation of zero, which is 0000. 13.3. Adding using two’s complements is normal but can lead to an overflow error.
    13.4. Two’s complement forms are self-complement.
    13.5. Any number 0 can be added to a positive number without changing the value, and any number 1 can be added to a negative number without changing the value.
    13.6. Subtraction can be converted to addition.

14. Overflow
    14.1. A condition when the result of a calculation is too large to fit into the number of bits defined for storage.

15. ASCII
    15.1. American Standard Code for Information Interchange.
    15.2. Non-printing or control characters are introduced to assist in data transmission or for data handling at a computer terminal.
    15.3. A code that uses seven bits in a byte.
    15.4. The majority of the codes are for characters of English text which are available on a standard keyboard.
    15.5. These include upper and lower letters, punctuation marks, denary digits, and arithmetic symbols.

16. Extended ASCII code
    16.1. A code that uses all eight bits in a byte.

17. Unicode
    17.1. developed in tandem with the ‘Universal character set’ scheme, standardized as ISO/IEC 10646. 17.2. The aim is to be able to represent any possible text.
    17.3. Each code is represented in one to four bytes.
    17.4. backward compatible with ASCII.
    17.5. variable width character encoding.

18. BCD
    18.1. Binary Coded Decimal.
    18.2. A form of binary representation where each denary digit is converted individually into binary, rather than the whole number being converted as a large number.
    18.3. It’s useful in applications that require single denary digits to be stored or transmitted.
    18.4. Since it only uses a nibble, there are two types of BCD: one BCD code in one byte, the rest digit filled with 0, or two BCD digits per byte, known as packed BCD.

19. Image
    19.1. Can be stored in a computer system for the eventual purpose of displaying the image on a screen or for presenting it on paper usually as a component of a document.
    19.2. Such an image can be created by using an appropriate graphic package, known as vector graphics.
    19.3. Alternatively, when an image already exists independently of the computer system, it can be captured by a scanner or camera into an image, known as a bitmap image.

20. Vector graphics
    20.1. An image is created by a drawing package or a CAD package.
    20.2. Each component is an individual drawing object.
    20.3. A vector graphics file contains a drawing list.
    20.4. The list contains a command for each object included in the image.
    20.5. Each command has a list of attributes.
    20.6. Each attribute defines a property of the object.
    20.7. Scalable.

21. CAD
    21.1. Computer-Aided Design.

22. Pixel
    22.1. The smallest identifiable component of bitmap.
    22.2. Each pixel has a color.

23. Image resolution
    23.1. The number of pixels is defined by the product of the width and height values.

24. Color depth
    24.1. The number of bits used to represent color.

25. Screen resolution
    25.1. The product of width and height values for the number of pixels that a screen can display.

26. Pixelation
    26.1. When a bitmap or a section of a bitmap is displayed at such a large size that individual pixels, the small single-colored square that comprise the bitmap are visible.

27. Analog signal
    27.1. A continuous signal which represents physical measurements.

28. Digital signal
    28.1. Generated by digital modulation.

29. Sampling rate
    29.1. The number of times per second data is recorded.

30. Sampling resolution
    30.1. The level of detail is recorded, and it’s determined by the number of bits that are used to store each sample.

31. Compression
    31.1. Can be used to reduce file size, use less storage and make the faster transmission.
    31.2. There are two types of compression: lossless and lossy.

32. Lossless compression
    32.1. No data was lost.
    32.2. Original data can be restored.
    32.3. The quality of the file is not affected.
    32.4. text or data must use lossless compression.
    32.5. Two examples are RLE and Huffman coding.

33. RLE
    33.1. Run-Length Encoding.
    33.2. A form of lossless data compression.
    33.3. Runs of data, namely the sequences in which the same data value occurs in many consecutive data elements, are stored as a single data value and count, rather than as the original run.
    33.4. For example: GGGRRRRRBBBBBBBB -> 3G5R8B

34. Huffman coding
    34.1. A form of lossless data compression.
    34.2. Assign variable-length codes to input characters, lengths of the assigned codes are based on the frequencies of corresponding characters.
    34.3. The most frequent character gets the smallest code and the least frequent character gets the largest code.

35. Lossy compression
    35.1. Some data are lost.
    35.2. Original data can never be restored.
    35.3. The quality of the file is reduced.

36. LAN
    36.1. Local Area Network.
    36.2. A network connecting computers in a single room, in a single building, or on a single site.
    36.3. Spans a small geographical area.
    36.4. Network connected by hubs and switches.
    36.5. A LAN is not necessarily connected to the internet.

37. WAN
    37.1. Wide Area Network.
    37.2. A network connecting computers on different sites, possibly a thousand kilometers apart.
    37.3. Created when LANs are connected.

38. Client-server model
    38.1. A distributed application structure that partitions tasks or workloads between servers and clients.

39. Server
    39.1. The provider of a resource or service.

40. Client
    40.1. The requesters of a resource or service.

41. P2P
    41.1. peer-to-peer
    41.2. No central device (server).
    41.3. Each peer has some parts of the files.
    41.4. Each peer can both act as a client and a server.
    41.4.1. Each peer can request file parts from others.
    41.4.2. Each peer can provide downloading of file parts for others.

42. Leach
    42.1. Any peer that downloads files without uploading anything in exchange.

43. Elements of communication
    43.1. A sender.
    43.2. A receiver.
    43.3. A transmission medium.
    43.4. A message.
    43.5. A protocol.

44. Protocol
    44.1. A set of rules must be agreed upon by the sender and the receiver for any communication transmitted over a network.

45. Data transmission
    45.1. The process of sending digital or analog data over a communication medium to one or more computing, network, communication, or electronic devices.
    45.2. There are three modes: simplex, half-duplex, and full-duplex.

46. Simplex
    46.1. Data is transmitted only in one direction; from the sender to the receiver.
    46.2. For example: TV receiving a broadcast.

47. Half-duplex
    47.1. Data is transmitted in both directions, but not at the same time.
    47.2. For example: walkie-talkie radio where you can only speak when the other doesn’t.

48. Full-duplex
    48.1. Data is transmitted in both directions at the same time.

49. Datacasting
    49.1. There are three types: unicast, multicast, and broadcast.

50. Unicast
    1.1. An illustration of unicast.
    50.1. Where a piece of information is sent from one point to another point.
    Multicast
    50.2. An illustration of multicast.
    50.3. Where a piece of information is sent from one or more points to a set of other points.

51. Broadcast
    51.1. An illustration of broadcast.
    51.2. Where a piece of information is sent from one point to all other points.

52. Network topology
    52.1. The arrangement of the devices of a communication network.
    52.2. There are five types that we need to remember: point-to-point, bus, mesh, star, and hybrid topology.

53. Point-to-point topology
    53.1. Two devices are connected to each other directly.

54. Bus topology
    54.1. An illustration of bus topology.
    54.2. Each end-system is connect by tap to main cable (bus).
    54.3. The end of the main cable is the terminator.
    54.4. If one end-system fails, the other are not affected.
    54.5. Relatively less expensive.
    54.6. Easy to set-up.

55. Mesh topology
    55.1. An illustration of full mesh topology.
    55.2. An illustration of partial mesh topology.
    55.3. Each end-system is connected to the other end-systems.
    55.4. All devices are interconnected with each other.
    55.5. The failure of one end-system leave the others unaffected.
    55.6. Relatively expensive.
    55.7. Hard to set-up.

56. Star topology
    56.1. Most common network topology.
    56.2. It has a centralized device (switch).
    56.3. Each end-system is connected to the central device directly.
    56.4. Any communication between two end-system must pass through the central device.
    56.5. A failure of any end-system leave the other unaffected.
    56.6. Less expensive compared to mesh topology.
    56.7. If the centralized device fails, the whole network fails.
    56.8. Expensive compared to bus topology.
    56.9. A star topology can use a hub/switch/router as the central device

57. Hybrid topology
    57.1. Combines two or more of the network topologies.
    57.2. Scalable.
    57.3. Complex.
    57.4. Hard to maintain.
    57.5. Relatively expensive.

58. NIC
    58.1. Network Interface Card.
    58.2. Used to connect your computer to a network.
    58.3. Has a MAC address, which is the MAC address of your computer.
    58.4. The MAC address is given by the manufacturer.

59. Hub
    59.1. Connects multiple computers or other network devices.
    59.2. No intelligence on where to send information and broadcasts all network.
    59.3. Detect basic network errors.

60. Switch
    60.1. Operates in the data-link layer but has no access to the network layer.

61. ARP
    61.1. Address Resolution Protocol

62. WiFi
    62.1. A term used to describe the wireless ethernet.
    62.2. WiFi uses radio frequency transmission.

63. Router
    63.1. A router forwards packets to their destination.
    63.2. A router examinates the header of each packet.
    63.3. The destination IP address and the routing table are used to decide the next hop.
    63.4. A router sends the packet on its next hop.

64. Computational thinking
    64.1. The mental skill to apply fundamental concepts and reasoning, derived from computing and computer science, to solve problems in all areas.
    64.2. Allow us to take a complex problem, understand what the problem is and develop possible solutions.
    64.3. Four cornerstones: decomposition, pattern recognition, abstraction, and algorithms.

65. Decomposition
    65.1. Breaking down a complex problem or system into smaller, more manageable parts.

66. Pattern recognition
    66.1. Looking for similarities among and within problems.

67. Abstraction
    67.1. Focusing on the important information only, ignoring irrelevant detail.

68. Algorithms
    68.1. Developing a step-by-step solution to the problem.
    68.2. The rules to follow to solve the problem.

69. Construct
    69.1. Four types: assignment, sequence, selection, and repetition.

70. Variables
    70.1. A storage location for a data value that has an identifier.

71. Embeded system
    71.1. An embeded system is a computer system that isn put into another device/system.
    71.2. It as a microcontroller/microprocessor.
    71.3. it is used for special purpose, not for general purpose. this means that it is desinged to perform a specific function.
    71.4. moden family appliances use embeded system.

72. The five stages in the program development life cycle:
    72.1. Analysis
    72.2. Design
    72.3. Coding
    72.4. Testing
    72.5. Maintenance

73. types of error
    73.1. syntax error: an error in which a program statement does not follow the rules of the language
    73.2. logic error: an error in the logic of the solution that causes it not to behave as intended
    73.3. run-time error: an error that causes program execution to crash or freeze

74. Testing method
    74.1. stub testing:
    74.1.1. stubs are computer programs that act as temporary replacement for a called basion module and give the same output as the actual product or software.
    74.1.2. stub testing: stubs are used to test programs before all the facilities have been implemented.
    74.2. black-tox testing: comparing expected result with actural results when a program is run
    74.3. white-box testing: testing every path throught the program code
    74.4. dry-run/walk through: the process of checking the execution of an algorithm or pgoram by recording variable values in a trace table.
    74.5. integration testing: software oftern consists of many modules, sometimes written by differenct programmers. each individual module might has passed all the tests, but when modules are joined together into one program, it is vital that the whole program is tested. This is know as integration testing.
    74.6. alpha testing: software will be tested in-house by software testers before being released to custormes.
    74.7. acceptance testing: this is for bespoke software. the customer will check that it meets the requirements and works as expected.
    74.8. beta testing:
    74.8.1. this is for the software for general sale.
    74.8.2. A version is released to a limited audience of potential users, known as ‘beta testers’.
    74.8.3. The beta testers will use the software and test it in their own environments.
    74.8.4. the users will feedback to the software house any problem they have found, sot that the software house can correct any reported faults.

75. data integrity: a requirement for data to be accurate and upto date

76. data privacy: a requirement for data to be available only to autherized users.

77. date security: a requirement for data to be availabe for use when needed, ensuers that only authourized users have access to the system and data can be recoved if lost of corrupted.