ASCII vs. Unicode: 4 Key Differences You Must Know

Its original development goal was partly similar to that of Unicode. ASCII was intended to serve as a common computer code that united the different computer models, which, until its introduction, encoded characters using varying proprietary systems.

ASCII was proposed by Bob Bemer, a computer scientist associated with IBM, in 1961. The system was approved in 1963 as the American standard. However, it did not enjoy wide acceptance immediately.

The original version of ASCII used seven-digit binary numbers, allowing it to represent 128 different characters. For instance, the binary sequence 1010000 represented an uppercase P.

With time, ASCII was exposed to further development, with revisions issued in 1965, 1967, 1968, 1977, and 1986.

ASCII relied on the underlying concept of bytes, or binary code arranged in groups of eight. Therefore, ASCII is generally embedded in eight-bit fields that consist of seven information bits and one parity bit for either checking errors or representing special symbols.

In 1981, IBM introduced extended ASCII. This eight-bit code was created for the first IBM PC and soon became the accepted standard for personal computers.

Extended ASCII features 32 code combinations for control and machine commands, another group for uppercase letters and some punctuation, another for numerals and other punctuation, and another for lowercase letters.

With the eight-bit system, ASCII could increase the number of characters represented to 256. This allowed all special characters and characters from some other languages to be represented.

However, even extended ASCII proved insufficient for supporting every written language, especially Asian languages that include thousands of characters in their scripts. It was this limitation that gave rise to the need for Unicode.

Unicode was created to encode the underlying characters and graphemes of various languages rather than all the variations in the character glyphs.

Its goal has been to transcend the constraints of ASCII and other traditional character encodings, like the ones defined by the ISO/IEC 8859 standard. This is because while these encodings were widely used in different countries, they were mostly incompatible with each other.

The origins of Unicode began in 1987 when personnel from Xerox and Apple began exploring the practicalities of establishing a universally accepted character set.

Unicode’s original 16-bit design was created assuming that it would be used only to encode the characters in contemporary use.

With time, the Unicode working group grew and onboarded members from more organizations, including Microsoft and Sun Microsystems. A large part of the mapping work for existing character encoding standards had been completed by 1991.

In the same year, the Unicode Consortium was incorporated in California. The first edition of the Unicode standard was published in October 1991. Less than a year later, in June 1992, the second volume was published, covering Han ideographs.

A surrogate character mechanism was added to Unicode 2.0 in 1996. This enhanced the Unicode codespace to more than a million code points, enabling numerous historical scripts and obscure or obsolete characters to be encoded.

ASCII and other older character encoding systems enable monolingual and, in certain instances, bilingual computer processing. However, Unicode goes a few steps ahead and offers support for multilingual processing, thus allowing arbitrary scripts from several distinct languages to be combined at the same time.

The representation of characters in ASCII is limited to the English language. It supports letters, numbers, and some common punctuation and symbols.

ASCII uses either 7 bits or 8 bits to represent various characters, which allows it to use less memory space than Unicode. The original version can only encode 128 characters using a 7-bit range, including non-printing control characters.

ASCII is a proper subset of Unicode, which means that Unicode includes all the characters that can be encoded in ASCII, plus many more. So, while ASCII is useful for representing characters in the English language, Unicode is capable of representing a much wider range of characters in other languages and scripts.

The term Unicode stands for “universal character encoding.” It is standardized by the international IT industry to be used to encode and represent characters in computers.

One of the key advantages of Unicode is its ability to represent a large number of characters and symbols, including mathematical formulas, historical scripts, and even emojis. This is possible because Unicode uses four different encoding formats, known as UTF-7, UTF-8, UTF-16, and UTF-32. These formats use 7, 8, 16, and 32 bits, respectively.

While these formats allow Unicode to represent a much wider range of characters than ASCII, it also means that Unicode consumes more memory. However, this is not a constraint for memory-rich modern-day IT infrastructure.

The latest version of Unicode encrypts 161 written scripts, including 94 modern and 67 historical or ancient scripts. Naturally, this makes it a superset of ASCII, meaning that all the characters in the ASCII character set are also included in the Unicode character set.

7-bit

ASCII was created as the national encoding standard for the US. Soon, other nations understood the need for their own versions of the standard — those that included letters and symbols from their local languages.

This led to the creation of ISO 646, a standard similar to ASCII but featuring extensions for various non-English characters.

ISO 646 provided numerous code points for “national use” characters. These characters were designed for adaptation per each country’s needs. However, it took four years for the International Organization for Standardization to accept the international recommendation.

This delay led to certain incompatibilities once other countries started creating their own assignments for the provided code points. While codes indicating the national variant being used were provided, they were seldom used in practice.

Subsequently, a major challenge faced by programmers from different countries was using one code point to represent different characters. For instance, programmers from Germany, France, and Sweden would use different code points for the same accented letters. This made interoperability difficult.

To address this issue, trigraphs were created in ANSI C (the standard for the C programming language). However, even they saw limited adoption due to late introduction and inconsistent implementation. As a result, users would see symbols such as brackets in the middle of words.

8-bit

With time, computers evolved from 12-bit, 18-bit, and 36-bit systems to 8-bit, 16-bit, 32-bit, and 64-bit systems. Soon, the 8-bit byte became the standard for storing characters in memory.

This allowed for the development of extended ASCII, which supported additional characters beyond the original 128 in the 7-bit version. Extended character sets were earmarked for different regions and systems.

For instance, ISCII was established for India and VISCII for Vietnam. These encodings were sometimes referred to as ASCII, but true ASCII is the standard as strictly defined by the American National Standards Institute.

However, even extended ASCII was not truly universal. Early personal computers would feature unique 8-bit character sets that would often replace control characters with graphics. For instance, Commodore International would use the PETSCII code based on an earlier version of ASCII.

ISO/IEC 8859

The printable characters provided for by ASCII were only enough to facilitate information exchange in modern English. Other languages with Latin alphabets require additional symbols not provided for in ASCII.

ISO/IEC 8859, derived from the Multinational Character Set (MCS), was introduced to address this issue — it utilized the eighth bit in 8-bit bytes to support another 96 printable characters.

The ISO/IEC 8859 standard became a popular character encoding standard. It saw extensions like Windows-1252 for adding typographic punctuation marks for text printing. However, since 2008, Unicode UTF-8 has become more common.

Compared to ASCII, which uses only one byte to represent a single character, Unicode uses up to four bytes. This gives it the capability to support a wide variety of encoding systems.

The three main encoding variants of Unicode are UTF-8, UTF-16, and UTF-32. Among them, UTF-8 is the default encoding variant for several programming languages.

UCS

The Universal Coded Character Set (UCS) is a standard collection of Unicode characters as defined by ISO/IEC 10646. While UCS-2 uses two bytes for character storage, UCS-4 uses four.

UTF

UTF stands for UCS Transformation Format. Unicode is split into four encoding variants — UTF-7, UTF-8, UTF-16, and UTF-32, which are the different Unicode standards. The number after UTF showcases the bits used to represent one character in that variant.

• UTF-7 uses 7 bits for each character shown. Its original purpose was the representation of ASCII characters in an email that leveraged Unicode encoding.

• UTF-8 is the most widely used variant of Unicode encoding. In UTF-8, one byte is used for regular English characters, while two are used for Middle Eastern and Latin characters and three for Asian characters. Four bytes may be used for representing certain additional characters. As the first 128 characters of UTF-8 are mapped to the same values as ASCII, it can be said that UTF-8 is backward compatible with ASCII.

• UTF-16 is an extension of UCS-2, using two bytes to represent 65,536 characters. Additionally, UTF-16 supports four bytes for characters up to one million.

• Finally, UTF-32 is a multibyte encoding variant representing its characters using 4 bytes.

This standard allowed developers to create globally applicable interfaces for humans and computers to understand each other.

Simply put, it works by coding data strings as ASCII characters and enabling their interpretation and display as readable plain text for humans and data for computers.

The design of the ASCII character set is also useful for programmers looking to simplify certain tasks. For instance, ASCII character codes make it easy to convert text from lowercase to uppercase and vice versa — all it takes is changing one bit.

And even though ASCII has been replaced by Unicode in most major applications, making it technically obsolete, the first 128 characters of UTF-8 use the same encoding as ASCII. In a way, ASCII continues to play an important role in one of the most popular encoding mediums in use today.

Before the existence of Unicode, programmers from across the world had developed many encodings, each for specific languages and purposes.

As the encoding landscape continued to sprawl out, interpreting inputs, sorting, storage, and display became a challenge.

Additionally, programs could handle either a single encoding at one time and switch among available options or convert between internal and external encodings.

These barriers among encoding standards meant data loss every time text was transferred from one machine to another.

Programs that contained both the data and the code for performing conversions among a subset of traditional encodings existed; however, they were heavy on memory use.

There was a clear lack of a central, authoritative source of precise definitions of encodings. The need for an encoding solution independent of all the various character sets and their encodings was felt.

Addressing all these challenges has been one of the most important achievements of Unicode.

This universal standard offers a central character set that can cater to all present-day languages.

It is built to ensure seamless interoperability with ASCII and ISO-8859-1, the two most popular character sets before it.

Unicode is the preferred standard for the internet, especially XML and HTML. It is also seeing adoption for email.

Finally, and most importantly, it is expandable — any characters not covered today can be added in the future.