Representing text: ASCII and Unicode

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Apuntes de la lección

What is Character Encoding?

Character encoding is a convention that uses a numeric value to represent each character in a writing script.
It covers natural language symbols, plus control characters and whitespace.
The numeric values are called code points; together they form a code space or code page.
Encoded text can be stored, transmitted, and transformed by computers.

Early Character Encodings

Early codes (e.g., Morse code, Baudot code) could only represent a limited set of characters, often just upper-case letters, numerals, and basic punctuation.
Morse code (1840s) used four symbols (short signal, long signal, short space, long space) to create variable-length codes.
Baudot code (1870) was a five-bit encoding, later standardized as ITA2 in 1930.
Punch cards (late 19th century) encoded data by hole positions; later, alphabetic data used multiple punches per column.
IBM's BCD (binary-coded decimal) encodings were six-bit and used in early computers like the IBM 702.

ASCII: The American Standard Code for Information Interchange

ASCII is a widely used character encoding that maps each character to a 7-bit binary code (0–127).
It includes upper and lower case letters, digits, punctuation, and control characters.
ASCII can represent only 128 characters, which is enough for English but not for other languages.
Because it uses 7 bits, ASCII text takes 1 byte per character (with the 8th bit often unused or used for parity).

Limitations of ASCII

ASCII cannot represent characters from non-English languages (e.g., accented letters, Cyrillic, Arabic, Chinese).
It also cannot represent emoji or many special symbols.
To overcome this, various extended ASCII encodings (like ISO/IEC 8859) were created, but they were incompatible with each other.
This led to the need for a universal encoding system.

Unicode: A Universal Character Set

Unicode is a comprehensive encoding system that aims to represent every character from all writing systems, plus emoji and symbols.
Each character has a unique code point (e.g., U+0041 for 'A').
Unicode is extensible, meaning new characters can be added.
It has replaced most earlier encodings because it solves the compatibility problem.

Text becomes computer-readable by mapping each character to a code point and then to binary.

Unicode Encoding Forms: UTF-8 and UTF-16

UTF-8 is the most popular encoding on the World Wide Web (used by 98.9% of surveyed sites as of January 2026).
UTF-8 uses variable-length encoding: characters take 1 to 4 bytes; ASCII characters take 1 byte, so it is backward-compatible with ASCII.
UTF-16 uses 2 or 4 bytes per character and is common in application programs and operating systems.
Both UTF-8 and UTF-16 can represent all Unicode characters.

How Text Size Relates to Length

The file size of text depends on the encoding and the characters used.
In ASCII, each character is 1 byte, so size in bytes equals the number of characters.
In UTF-8, characters may be 1 to 4 bytes; for example, 'A' is 1 byte, 'é' is 2 bytes, and an emoji is 4 bytes.
In UTF-16, most characters are 2 bytes, but some (like emoji) are 4 bytes.
Thus, the same text can have different byte sizes in different encodings.

Why Unicode Matters

Unicode allows computers to handle multiple languages and scripts in a consistent way.
It enables global communication and software that works worldwide.
It supports emoji and other symbols, making digital text more expressive.
Without Unicode, text would be garbled when moving between systems using different encodings.

Unicode covers the world writing systems and emoji in one standard, where ASCII covers only basic Latin.

Diapositivas

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Preguntas de práctica

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1.What does ASCII stand for?
Easy
- AAmerican Standard Code for Information Interchange
- BAmerican System for Computer and Internet Interchange
- CAutomated Standard Code for Information Interchange
- DAmerican Standard Computer Interface Interchange
2.Which character encoding system is the most popular on the World Wide Web as of January 2026?
Easy
- AASCII
- BUTF-8
- CUTF-16
- DEBCDIC
3.ASCII can represent characters from all written languages in the world.
Easy
True or false?
4.Unicode is an extensible encoding system that has replaced most earlier character encodings.
Easy
True or false?
5.Why is Unicode preferred over ASCII for representing text in modern applications?
Medium
- AUnicode is faster to process than ASCII.
- BUnicode uses fewer bits per character.
- CUnicode can represent characters from many different languages and scripts.
- DUnicode is simpler and easier to implement.
6.Which of the following are examples of character encoding systems? (Select all that apply)
Medium
- AMorse code
- BBaudot code
- CPunch card
- DASCII
- EUnicode
7.ASCII was designed to represent all characters in all human languages.
Easy
True or false?
8.Match each character encoding system to its correct description.
Easy
- ASCII
- Unicode
- Baudot code
- An early 5-bit code used in telegraphy
- A 7-bit code for English characters
- An extensible system covering most world scripts

Más preguntas

9.Arrange these character encoding developments in chronological order (earliest to latest).
Medium
- Morse code
- Baudot code
- ASCII
- Unicode
10.Which of the following are character encoding systems? (Select all that apply)
Easy
- AMorse code
- BBaudot code
- CPunch cards
- DASCII
- EUnicode
11.The numerical values that make up a character encoding are known as code points.
Easy
True or false?
12.The Baudot code is a seven-bit encoding scheme.
Easy
True or false?
13.Match each encoding or code to its characteristic bit length or type.
Medium
- Baudot code
- ASCII
- Unicode
- 5-bit
- 7-bit
- Variable-length or 16/32-bit
14.Put these steps in the correct order for how character encoding works:
Medium
- A character is assigned a code point
- The code point is stored as binary data
- The binary data is transmitted or stored
- The binary data is decoded back to the character
15.Which of the following are limitations of early character encodings like ASCII? (Select all that apply)
Medium
- AThey could only represent a subset of characters used in languages
- BThey often restricted to upper case letters, numerals and limited punctuation
- CThey could not represent emoji or many world scripts
- DThey were all variable-length codes
16.Morse code uses a system of four symbols: short signal, long signal, short space, and long space.
Easy
True or false?
17.According to the source, which encoding uses a five-bit code?
Medium
- AMorse code
- BBaudot code
- CASCII
- DUTF-8
18.The Baudot code was standardized as International Telegraph Alphabet No. 2 (ITA2) in 1930.
Easy
True or false?
19.Which of the following is NOT listed as a common example of a character encoding system in the source?
Medium
- AMorse code
- BBaudot code
- CEBCDIC
- DUnicode
20.The most popular character encoding on the World Wide Web is UTF-16.
Easy
True or false?
21.As of January 2026, what percentage of surveyed websites use UTF-8?
Medium
- A89.8%
- B98.9%
- C99.8%
- D88.9%
22.What is the primary reason that early character encodings like ASCII could not represent all world languages?
Easy
- AThey used variable-length codes that were too slow to decode.
- BThey only used a limited number of bits, restricting the number of possible characters.
- CThey were designed only for telegraphy, not for computers.
- DThey used symbols instead of binary numbers.
23.Match each encoding system to its characteristic bit length or type.
Medium
- Morse code
- Baudot code
- EBCDIC
- Variable-length symbols
- Five-bit code
- Eight-bit code
24.Character encoding is a convention of using a numeric value to represent each character of a writing script.
Easy
True or false?
25.A character set can only include natural language symbols, not control characters or whitespace.
Easy
True or false?
26.Early character encodings could represent all characters used in all languages.
Easy
True or false?
27.Which of the following is NOT an example of a character encoding system listed in the source?
Easy
- AMorse code
- BBaudot code
- CASCII
- DHTML
28.Match each character encoding system to its characteristic bit length or type.
Medium
- Morse code
- Baudot code
- EBCDIC
- Variable-length code
- Five-bit code
- Eight-bit code
29.Arrange these character encoding systems in chronological order of their introduction (earliest to latest).
Medium
- Morse code
- Baudot code
- ASCII
- EBCDIC
30.Match each encoding system to its correct description.
Medium
- Morse code
- Baudot code
- EBCDIC
- Uses four symbols: short signal, long signal, short space, long space
- Five-bit code created by Émile Baudot
- Eight-bit code developed for IBM System/360
31.Put the following steps in the correct order for how character encoding works.
Medium
- Each character is assigned a numeric code point.
- The code point is stored as binary data.
- A character set defines the available characters.
- The binary data is decoded back to the character when needed.
32.The most popular character encoding on the World Wide Web is UTF-8, used in 98.9% of surveyed websites as of January 2026.
Medium
True or false?
33.The Baudot code uses a fixed length of 5 bits per character, and it can represent up to 32 distinct characters.
Medium
True or false?
34.Which of the following character encodings uses a variable-length scheme?
Medium
- AASCII
- BBaudot code
- CUTF-8
- DEBCDIC
35.The Baudot code uses a fixed length of 5 bits per character.
Easy
True or false?
36.Which of the following is a limitation of the Baudot code that caused compatibility issues?
Medium
- AIt used variable-length codes.
- BIt could not represent digits.
- CIt suffered from shortcomings and was often modified by manufacturers, causing compatibility issues.
- DIt was not standardized.
37.Why were six-bit BCD encodings sufficient for IBM's early electronic computers?
Medium
- ABecause the punched card code was limited to digits, upper-case English letters, and a few special characters.
- BBecause six bits can represent all Unicode characters.
- CBecause they needed to encode lower-case letters and many symbols.
- DBecause they used variable-length codes.
38.Which of the following is NOT a common example of a character encoding system?
Easy
- AMorse code
- BBaudot code
- CASCII
- DHTML
39.A character set can include control characters and whitespace, not just natural language symbols.
Easy
True or false?
40.Which of the following is a five-bit encoding created by Émile Baudot?
Easy
- AMorse code
- BBaudot code
- CASCII
- DUnicode
41.What is the term for the numerical value that represents a character in a character encoding system?
Easy
42.Complete the sentence about character encoding.
Easy
The numerical values that make up a character encoding are known as ____.
43.Fill in the blanks with the correct encoding systems.
Medium
Two common examples of character encoding systems are ____ and ____.
44.Name one limitation of ASCII that led to the development of Unicode.
Medium
45.Complete the sentence using the correct term from the source.
Easy
The numerical values that make up a character encoding are known as ____.
46.Name the character encoding that uses a 5-bit code and was created by Émile Baudot.
Easy
47.According to the source, what percentage of surveyed websites use UTF-8 as of January 2026?
Medium
48.How many bits are used in the Baudot code?
Easy
49.What is the name of the encoding system developed in 1963 for the IBM System/360 that featured a larger character set including lower case letters?
Medium
50.In Morse code, how many distinct symbols are used to represent characters?
Medium
51.Who created the Baudot code?
Easy
52.What is the name of the encoding system that has replaced most earlier character encodings?
Easy
53.Explain how the character 'A' might be represented in ASCII and why Unicode is more flexible.
Medium
54.Explain why Unicode has replaced most earlier character encodings.
Hard
55.Describe how punch card data encoding evolved from Hollerith's initial design to later alphabetic representation, and explain why six-bit BCD codes were sufficient at that time.
Hard
56.Explain why Unicode is preferred over ASCII for representing text in modern applications.
Medium
57.Explain why early character encodings like ASCII could not represent all world languages, and how Unicode addresses this limitation.
Hard
58.According to the source, what percentage of surveyed websites use UTF-8 as of January 2026?
Medium
- A89 %
- B98.9 %
- C108.8 %
- D118.7 %
59.How many bits are used in the Baudot code?
Easy
- A7 bits
- B5 bits
- C6 bits
- D4 bits
60.In Morse code, how many distinct symbols are used to represent characters?
Medium
- A4 symbols
- B6 symbols
- C3 symbols
- D5 symbols

Apuntes de repaso

## Representing Text: ASCII and Unicode ### Character Encoding Basics - **Character encoding** is a convention that uses a numeric value (a **code point**) to represent each character in a writing script. - Code points collectively form a **code space** or **code page**. - Encodings can include letters, digits, punctuation, control characters, whitespace, and symbols from constructed languages. - Encoded text can be stored, transmitted, and processed by computers. ### ASCII - **ASCII** (American Standard Code for Information Interchange) is a character encoding that uses **7 bits** to represent **128 characters** (0–127). - It includes upper and lower case English letters, digits, punctuation, and control characters. - **Limitation**: ASCII can only represent a limited set of characters (mainly English), so it cannot handle other scripts (e.g., Greek, Arabic) or emoji. ### Unicode - **Unicode** is a modern, extensible encoding system that aims to represent every character from all writing systems, plus symbols and emoji. - It uses **code points** that can be encoded in different ways, such as **UTF-8** and **UTF-16**. - **UTF-8** is the most popular encoding on the World Wide Web (used by 98.9% of surveyed websites as of January 2026). - UTF-8 uses **variable-length** encoding: common characters (like ASCII) use 1 byte, while others use 2, 3, or 4 bytes. ### Text Size in Bytes - The size of text in bytes depends on the encoding and the characters used. - For example, in UTF-8: - 'A' (ASCII) = 1 byte - 'é' (Latin-1) = 2 bytes - '中' (CJK) = 3 bytes - Emoji (e.g., 😀) = 4 bytes - So, the number of bytes is not always equal to the number of characters. ### Key Takeaway - ASCII is limited to 128 characters; Unicode (especially UTF-8) supports virtually all scripts and symbols, making it the standard for modern computing and the web.

Character encoding: A convention of using a numeric value to represent each character of a writing script.
Code point: The numerical value that represents a character in a character encoding.
Code space / code page: The collective set of code points in a character encoding.
ASCII: American Standard Code for Information Interchange; a 7-bit character encoding that represents 128 characters, including English letters, digits, and punctuation.
Unicode: A well-defined and extensible encoding system that has replaced most earlier character encodings, supporting a vast range of characters from world scripts, symbols, and emoji.
UTF-8: A variable-length Unicode encoding that uses 1 to 4 bytes per character; the most popular encoding on the World Wide Web.
UTF-16: A Unicode encoding that uses 2 or 4 bytes per character; commonly used in application programs and operating systems.

Tarjetas

What is a character set in computing?

A character set is a collection of characters (letters, digits, symbols, control characters) that a computer can represent, each mapped to a unique numeric code.

What is a code point?

A code point is the numeric value assigned to a character in a character encoding, such as 65 for 'A' in ASCII.

What does ASCII stand for?

ASCII stands for American Standard Code for Information Interchange.

How many bits does ASCII use to represent each character?

ASCII uses 7 bits per character, allowing 128 different characters (2⁷ = 128).

What is the range of ASCII code points?

ASCII code points range from 0 to 127, covering English letters, digits, punctuation, and control characters.

What is a major limitation of ASCII?

ASCII can only represent 128 characters, which is insufficient for languages with non-Latin scripts (e.g., Chinese, Arabic) and many symbols like emoji.

What is Unicode?

Unicode is a comprehensive character encoding standard that assigns a unique code point to virtually every character in all human languages, including emoji and historical scripts.

What are UTF-8 and UTF-16?

UTF-8 and UTF-16 are Unicode transformation formats that encode Unicode code points into binary. UTF-8 uses variable-length encoding (1-4 bytes), while UTF-16 uses 2 or 4 bytes per character.

Which Unicode encoding is most popular on the web?

UTF-8 is the most popular, used by 98.9% of surveyed websites as of January 2026.

How does the size of text in bytes relate to its length in Unicode?

In UTF-8, the number of bytes per character varies: ASCII characters use 1 byte, but characters from other scripts may use 2-4 bytes, so byte size is not always equal to character count.

What is a control character?

A control character is a non-printable character in a character set that performs a function, such as newline, tab, or carriage return.

What is a code space or code page?

A code space (or code page) is the complete set of code points defined by a character encoding, such as 0-127 for ASCII.

What was the Baudot code?

The Baudot code is an early 5-bit character encoding invented by Émile Baudot in 1870, used in telegraphy, and later standardized as ITA2.

What is EBCDIC?

EBCDIC (Extended Binary-Coded Decimal Interchange Code) is an 8-bit character encoding developed by IBM in 1963 for the System/360, supporting more characters than earlier 6-bit codes.

Why were early character encodings limited?

Early encodings were limited by hardware constraints, often using only 5 or 6 bits, which could represent only a small set of characters like uppercase letters and digits.

What is the difference between ASCII and Unicode?

ASCII is a 7-bit encoding for 128 characters, while Unicode is a comprehensive standard with over a million code points, supporting many scripts and symbols. ASCII is a subset of Unicode.

How many characters can Unicode represent?

Unicode can represent over 1.1 million code points, though not all are assigned yet.

What is a variable-length encoding?

A variable-length encoding uses different numbers of bits or bytes for different characters, like UTF-8 which uses 1-4 bytes per character, to save space for common characters.

What is the purpose of character encoding?

Character encoding allows computers to store, transmit, and process text by mapping each character to a numeric code that can be represented in binary.

What is the ASCII code for the letter 'A'?

The ASCII code for 'A' is 65 in decimal, or 1000001 in binary.

How many bits are in a byte?

A byte consists of 8 bits.

Why is UTF-8 popular on the web?

UTF-8 is backward-compatible with ASCII, uses less space for common Latin characters, and can represent all Unicode characters, making it efficient and widely supported.

What is a character encoding?

A character encoding is a convention that maps each character in a character set to a numeric value (code point) so that text can be stored and processed digitally.

What is the difference between a character set and a character encoding?

A character set is the collection of characters and their code points, while a character encoding is the scheme for representing those code points in binary (e.g., UTF-8).

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