ASCII vs. Unicode: A full tutorial

By Eyal Katz March 29, 2023

The encoding scheme you choose as a developer can have far-reaching consequences for your application’s functionality, security, and performance–in other words, it could be the difference between a seamless user experience and a catastrophic data failure. 

ASCII is a popular choice, with over 95% of all websites using it, and Unicode is quickly gaining ground for many applications on over 60% of websites. This article focuses on these two, even though there are many other encoding options to consider.

Whether you’re developing a website, mobile app, or software, choosing the right scheme for your use case is essential. Let’s demystify the worlds of ASCII and Unicode encoding to ensure your next project is successful.

Encoding in Web Development

Encoding schemes define how characters and symbols are represented in digital form, which impacts how data is stored, processed, and transmitted. That’s why developers need to choose an encoding scheme that best fits the specific requirements of their use case, be it a software, website, or mobile app.

Encoding should not be confused with encryption or hashing. Encryption is converting data into code to protect it from unauthorized access. For example, encryption secures sensitive information such as passwords, credit card numbers, and personal data. On the other hand, hashing is a one-way function that converts data into a fixed-length string of characters. For example, hashing is commonly used to store passwords securely in a database.

What is ASCII?


Although still widely used, ASCII (American Standard Code for Information Interchange) was developed in the 1960s as the first major character encoding standard for data processing. It is used to represent numbers (0-9), the English alphabet (A-Z) in uppercase and lowercase, and some symbols (including punctuation marks).

Despite its popularity, ASCII has some limitations. A major one is that it can only be used to encode characters in the English language, making it impractical for languages that use different alphabets and characters, such as Hebrew, Arabic, Hindi, Japanese, and Chinese.

Still, as we’ll see, ASCII is supported by most modern computer systems and is the basis for many other character encoding standards, including Unicode.

How Does ASCII Work?

ASCII uses 7 bits to represent a total of 128 characters. With the widespread use of 8-bit computers, an extended ASCII table was developed that uses 8 bits to represent 256 characters.Each character is assigned a unique numerical value (an ASCII code) ranging from 0 to 127. For example, the ASCII code for the letter “A” is 65, while the ASCII code for the number “1” is 49.

ASCII 7 bits

When data is encoded using ASCII, each character in the text is converted into its corresponding ASCII code, which is then stored as a sequence of binary digits (0s and 1s). This binary representation of the data can be transmitted from one computer to another, where it can be decoded back into the original text.

ASCII Decoding

Pros of ASCII

  • Universal acceptance: ASCII is a widely recognized and universally accepted standard for encoding text data, making it ideal for data communication and exchange between computer systems and applications.
  • Simplifies communication: ASCII allows developers to design interfaces that both humans and computers can understand, making it easier to communicate between different systems.
  • Efficient for programming: ASCII is a simple and efficient encoding standard, making it ideal for programming. It uses a limited number of characters, which helps to simplify specific tasks, and its 7-bit encoding allows for quick and efficient data processing.
  • Legacy support: ASCII has been around for several decades and is still widely used, which means that many older systems and applications still rely on ASCII, making it a valuable tool for developers who need to work with older systems.
  • Low resource usage: ASCII requires fewer bits to represent each character, requiring less storage and bandwidth for data transmission, making it ideal for applications that use limited resources.
  • Robustness: ASCII is a robust encoding standard that is less prone to errors and data corruption than other encoding standards, which makes it a reliable option for developers who need to ensure the accuracy and reliability of their data.

Cons of ASCII

  • Limited character set: the inability to encode characters beyond the English alphabet can lead to problems encoding data in other languages, leading to data corruption or loss.
  • Outdated: ASCII was created at a time when the use of computers was not widespread, and as such, it needs to consider the increasing number of languages and characters used in modern computing. This means that it may not be suitable for use in modern applications that need to support a wide range of characters and languages.
  • Vulnerability to data corruption: ASCII uses a 7-bit encoding system, which makes it vulnerable to data corruption. For example, suppose one of the bits in an ASCII-encoded character is lost or changed. In that case, the receiving system may not correctly interpret the character, leading to data corruption or loss.

Insecurity: ASCII is also vulnerable to security issues, such as character substitution attacks, where a malicious actor replaces characters in the data to alter its meaning or cause harm. This is a particularly serious issue in applications that transmit sensitive information, such as financial transactions or medical records.

Unicode Table

Unicode is a computing industry standard introduced to address the limitations of character encoding systems such as ASCII. It provides a standardized, universal character set that covers various characters in different scripts and languages, including Latin, Greek, Cyrillic, Hebrew, Arabic, Hindi, Chinese, and many more.

Unicode contains over 100,000 characters, making it possible to encode text in any written language used today. Using several encoding formats known as UTF (Unicode Transformation Format), Unicode can represent characters as binary data that computers can process. UTF-8 is the most widely used encoding format for web content.

Unicode has become the standard for character encoding in the computing industry, and its widespread use has helped to eliminate data exchange problems between systems that use different encoding systems. In addition, it allows developers to create user-friendly interfaces that can be used by people speaking different languages, and it helps to simplify tasks related to data processing and information management.

How does Unicode work?

Unicode assigns a unique number, called a code point, to each character in the universal character set. These code points represent the characters in binary form using one of the encoding formats specified by Unicode, such as UTF-8, UTF-16, or UTF-32.

When text is stored in a computer system, the code points for each character are first assigned and then encoded into a binary form using one of the Unicode encoding formats. The encoding format determines the number of bytes used to represent each character and affects the storage space required and the processing speed.

When text is displayed, the binary representation of the code points is decoded back into characters, which can then be displayed on the screen. The process of encoding and decoding ensures that the text is stored and transmitted accurately, regardless of the platforms, applications, or languages involved.

Pros of Unicode

  • It can represent more characters than ASCII, including symbols, emojis, and characters from different scripts and languages
  • Enables internationalization and localization, making it easier to develop applications for a global audience
  • Better compatibility with modern computer systems and devices
  • It offers consistency in encoding and representation, reducing the chances of compatibility issues
ASCII vs Unicode Characters

Cons of Unicode

  • Complexity in implementation compared to ASCII
  • Increased memory requirements compared to ASCII, as Unicode characters require more bytes to be stored
  • Potentially slow performance in certain applications or systems that require high-speed encoding and decoding
  • Unicode is vulnerable to Unicode encoding attacks, which exploit flaws in the decoding mechanism implemented on applications when decoding Unicode data format. Attackers use this technique to encode characters in the URL to bypass application filters, accessing restricted resources on the Web server or force browsing to protected pages. This may also lead to privilege escalation, arbitrary code execution, data modification, and denial of service.

Some legacy systems may not fully support Unicode, leading to compatibility issues and the need for conversion and migration to newer systems.

Unicode compatibility Issues

The verdict: Things every developer should know about text encodings

Here are some factors to consider when choosing between ASCII and Unicode for your specific use case:

  • Language support: If your project requires support for multiple languages, especially those that use characters not included in the ASCII character set, Unicode is the better choice.
  • Storage requirements: If storage space is a concern, ASCII might be a better choice as it requires less scalability than Unicode.
  • Data transmission: If the data is transmitted through electronic communication channels, such as text messages, ASCII might be a better choice because it uses less bandwidth than Unicode.
  • Compatibility with existing systems: consider what systems your project will need to integrate with since ASCII is widely supported by older, legacy systems, and Unicode is commonly used in modern systems.
ASCII vs Unicode pros and cons

Plans: when considering the project’s future, remember that Unicode is the standard for modern computing and can represent a wider range of characters than ASCII. To put things in perspective, take the booming popularity of emojis, used by 92% of people online, according to the Unicode Consortium. Unicode can give you the flexibility to accommodate these types of trends if user experience is top of mind for you.

A Short History of the Emoji

Build and ship software without worry

When selecting the right encoding system for your DevOps project, it is critical to consider language support, storage requirements, data transmission, compatibility, security and plans. But don’t let security be an after-thought. Matching early encoding decisions with automated security solutions could improve results, code safety, and long-term trust. For example, a solution like Spectral can help developers detect hard-coded secrets and prevent source code leakage, a common problem associated with encoding. To code confidently while protecting your company from expensive mistakes, learn more and get started with a free account today.

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