What s the difference between ASCII and Unicode

Question

What s the exact difference between Unicode and ASCII   ASCII has a total of 128 characters  256 in the extended set    Is there any size specification for Unicode characters

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ASCII and Unicode are two character encodings. Basically, they are standards on how to represent difference characters in binary so that they can be written, stored, transmitted, and read in digital media. The main difference between the two is in the way they encode the character and the number of bits that they use for each. ASCII originally used seven bits to encode each character. This was later increased to eight with Extended ASCII to address the apparent inadequacy of the original. In contrast, Unicode uses a variable bit encoding program where you can choose between 32, 16, and 8-bit encodings. Using more bits lets you use more characters at the expense of larger files while fewer bits give you a limited choice but you save a lot of space. Using fewer bits (i.e. UTF-8 or ASCII) would probably be best if you are encoding a large document in English.

One of the main reasons why Unicode was the problem arose from the many non-standard extended ASCII programs. Unless you are using the prevalent page, which is used by Microsoft and most other software companies, then you are likely to encounter problems with your characters appearing as boxes. Unicode virtually eliminates this problem as all the character code points were standardized.

Another major advantage of Unicode is that at its maximum it can accommodate a huge number of characters. Because of this, Unicode currently contains most written languages and still has room for even more. This includes typical left-to-right scripts like English and even right-to-left scripts like Arabic. Chinese, Japanese, and the many other variants are also represented within Unicode. So Unicode won’t be replaced anytime soon.

In order to maintain compatibility with the older ASCII, which was already in widespread use at the time, Unicode was designed in such a way that the first eight bits matched that of the most popular ASCII page. So if you open an ASCII encoded file with Unicode, you still get the correct characters encoded in the file. This facilitated the adoption of Unicode as it lessened the impact of adopting a new encoding standard for those who were already using ASCII.

Summary:

1.ASCII uses an 8-bit encoding while Unicode uses a variable bit encoding.
2.Unicode is standardized while ASCII isn’t.
3.Unicode represents most written languages in the world while ASCII does not.
4.ASCII has its equivalent within Unicode.

Taken From: http://www.differencebetween.net/technology/software-technology/difference-between-unicode-and-ascii/#ixzz4zEjnxPhs

User · Answer

java provides support for Unicode i e it supports all world wide alphabets  Hence the size of char in java is 2 bytes  And range is 0 to 65535

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Storage     Given numbers are only for storing 1 character    ASCII   27 bits  1 byte    Extended ASCII   28 bits  1 byte    UTF-8   minimum 28  maximum 232 bits  min 1  max 4 bytes    UTF-16   minimum 216  maximum 232 bits  min 2  max 4 bytes    UTF-32   232 bits  4 bytes      Usage  as of Feb 2020

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Beyond how UTF is a superset of ASCII  another good difference to know between ASCII and UTF is in terms of disk file encoding and data representation and storage in random memory   Programs know that given data should be understood as an ASCII or UTF string either by detecting special byte order mark codes at the start of the data  or by assuming from programmer intent that the data is text and then checking it for patterns that indicate it is in one text encoding or another   Using the conventional prefix notation of 0x for hexadecimal data  basic good reference is that ASCII text starts with byte values 0x00 to 0x7F representing one of the possible ASCII character values   UTF text is normally indicated by starting with the bytes 0xEF 0xBB 0xBF for UTF8   For UTF16  start bytes 0xFE 0xFF  or 0xFF 0xFE are used  with the endian-ness order of the text bytes indicated by the order of the start bytes   The simple presence of byte values that are not in the ASCII range of possible byte values also indicates that data is probably UTF   There are other byte order marks that use different codes to indicate data should be interpreted as text encoded in a certain encoding standard

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ASCII defines 128 characters  which map to the numbers 0 ndash 127  Unicode defines  less than  221 characters  which  similarly  map to numbers 0 ndash 221  though not all numbers are currently assigned  and some are reserved    Unicode is a superset of ASCII  and the numbers 0 ndash 127 have the same meaning in ASCII as they have in Unicode  For example  the number 65 means  Latin capital  A     Because Unicode characters don t generally fit into one 8-bit byte  there are numerous ways of storing Unicode characters in byte sequences  such as UTF-32 and UTF-8

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ASCII defines 128 characters  as Unicode contains a repertoire of more than 120 000 characters

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Understanding why ASCII and Unicode were created in the first place helped me understand the differences between the two  ASCII  Origins As stated in the other answers  ASCII uses 7 bits to represent a character  By using 7 bits  we can have a maximum of 2 7    128  distinct combinations   Which means that we can represent 128 characters maximum   Wait  7 bits  But why not 1 byte  8 bits   The last bit  8th  is used for avoiding errors as parity bit  This was relevant years ago   Most ASCII characters are printable characters of the alphabet such as abc  ABC  123    amp    etc  The others are control characters such as carriage return  line feed  tab  etc  See below the binary representation of a few characters in ASCII  0100101 - gt     Percent Sign - 37  1000001 - gt  A  Capital letter A - 65  1000010 - gt  B  Capital letter B - 66  1000011 - gt  C  Capital letter C - 67  0001101 - gt  Carriage Return  13   See the full ASCII table over here  ASCII was meant for English only   What  Why English only  So many languages out there  Because the center of the computer industry was in the USA at that time  As a consequence  they didn t need to support accents or other marks such as                 etc   aka diacritics    ASCII Extended Some clever people started using the 8th bit  the bit used for parity  to encode more characters to support their language  to support  quot    quot   in French  for example   Just using one extra bit doubled the size of the original ASCII table to map up to 256 characters  2 8   256 characters   And not 2 7 as before  128   10000010 - gt      e with acute accent - 130  10100000 - gt      a with acute accent - 160   The name for this  quot ASCII extended to 8 bits and not 7 bits as before quot  could be just referred as  quot extended ASCII quot  or  quot 8-bit ASCII quot   As  Tom pointed out in his comment below there is no such thing as  quot extended ASCII quot  yet this is an easy way to refer to this 8th-bit trick  There are many variations of the 8-bit ASCII table  for example  the ISO 8859-1  also called ISO Latin-1  Unicode  The Rise ASCII Extended solves the problem for languages that are based on the Latin alphabet    what about the others needing a completely different alphabet  Greek  Russian  Chinese and the likes  We would have needed an entirely new character set    that s the rational behind Unicode  Unicode doesn t contain every character from every language  but it sure contains a gigantic amount of characters  see this table   You cannot save text to your hard drive as  quot Unicode quot   Unicode is an abstract representation of the text  You need to  quot encode quot  this abstract representation  That s where an encoding comes into play  Encodings  UTF-8 vs UTF-16 vs UTF-32 This answer does a pretty good job at explaining the basics   UTF-8 and UTF-16 are variable length encodings  In UTF-8  a character may occupy a minimum of 8 bits  In UTF-16  a character length starts with 16 bits  UTF-32 is a fixed length encoding of 32 bits   UTF-8 uses the ASCII set for the first 128 characters  That s handy because it means ASCII text is also valid in UTF-8  Mnemonics   UTF-8  minimum 8 bits  UTF-16  minimum 16 bits  UTF-32  minimum and maximum 32 bits   Note   Why 2 7    This is obvious for some  but just in case  We have seven slots available filled with either 0 or 1  Binary Code   Each can have two combinations  If we have seven spots  we have 2   2   2   2   2   2   2   2 7   128 combinations  Think about this as a combination lock with seven wheels  each wheel having two numbers only   Source  Wikipedia  this great blog post and Mocki co where I initially posted this summary

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ASCII has 128 code positions  allocated to graphic characters and control characters  control codes    Unicode has 1 114 112 code positions  About 100 000 of them have currently been allocated to characters  and many code points have been made permanently noncharacters  i e  not used to encode any character ever   and most code points are not yet assigned   The only things that ASCII and Unicode have in common are  1  They are character codes  2  The 128 first code positions of Unicode have been defined to have the same meanings as in ASCII  except that the code positions of ASCII control characters are just defined as denoting control characters  with names corresponding to their ASCII names  but their meanings are not defined in Unicode   Sometimes  however  Unicode is characterized  even in the Unicode standard   as    wide ASCII     This is a slogan that mainly tries to convey the idea that Unicode is meant to be a universal character code the same way as ASCII once was  though the character repertoire of ASCII was hopelessly insufficient for universal use   as opposite to using different codes in different systems and applications and for different languages   Unicode as such defines only the    logical size    of characters  Each character has a code number in a specific range  These code numbers can be presented using different transfer encodings  and internally  in memory  Unicode characters are usually represented using one or two 16-bit quantities per character  depending on character range  sometimes using one 32-bit quantity per character

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ASCII has 128 code points  0 through 127   It can fit in a single 8-bit byte  the values 128 through 255 tended to be used for other characters   With incompatible choices  causing the code page disaster   Text encoded in one code page cannot be read correctly by a program that assumes or guessed at another code page   Unicode came about to solve this disaster   Version 1 started out with 65536 code points  commonly encoded in 16 bits   Later extended in version 2 to 1 1 million code points   The current version is 6 3  using 110 187 of the available 1 1 million code points   That doesn t fit in 16 bits anymore   Encoding in 16-bits was common when v2 came around  used by Microsoft and Apple operating systems for example   And language runtimes like Java   The v2 spec came up with a way to map those 1 1 million code points into 16-bits   An encoding called UTF-16  a variable length encoding where one code point can take either 2 or 4 bytes   The original v1 code points take 2 bytes  added ones take 4     Another variable length encoding that s very common  used in  nix operating systems and tools is UTF-8  a code point can take between 1 and 4 bytes  the original ASCII codes take 1 byte the rest take more   The only non-variable length encoding is UTF-32  takes 4 bytes for a code point   Not often used since it is pretty wasteful   There are other ones  like UTF-1 and UTF-7  widely ignored   An issue with the UTF-16 32 encodings is that the order of the bytes will depend on the endian-ness of the machine that created the text stream   So add to the mix UTF-16BE  UTF-16LE  UTF-32BE and UTF-32LE   Having these different encoding choices brings back the code page disaster to some degree  along with heated debates among programmers which UTF choice is  best    Their association with operating system defaults pretty much draws the lines   One counter-measure is the definition of a BOM  the Byte Order Mark  a special codepoint  U FEFF  zero width space  at the beginning of a text stream that indicates how the rest of the stream is encoded   It indicates both the UTF encoding and the endianess and is neutral to a text rendering engine   Unfortunately it is optional and many programmers claim their right to omit it so accidents are still pretty common

[unicode] What's the difference between ASCII and Unicode?

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