Is ASCII code 7-bit or 8-bit

Question

My teacher told me ASCII is 8-bit character coding scheme  But it is defined only for 0-127 codes which means it can be fit into 7-bits  So can t it be argued that ASCII bit is actually 7-bit code   And what do we mean to say at all when saying ASCII is 8-bit code at all

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On Linux man ascii says      ASCII is the American Standard Code for Information Interchange   It is a 7-bit code

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ASCII was indeed originally conceived as a 7-bit code   This was done well before 8-bit bytes became ubiquitous  and even into the 1990s you could find software that assumed it could use the 8th bit of each byte of text for its own purposes   not 8-bit clean     Nowadays people think of it as an 8-bit coding in which bytes 0x80 through 0xFF have no defined meaning  but that s a retcon   There are dozens of text encodings that make use of the 8th bit  they can be classified as ASCII-compatible or not  and fixed- or variable-width   ASCII-compatible means that regardless of context  single bytes with values from 0x00 through 0x7F encode the same characters that they would in ASCII   You don t want to have anything to do with a non-ASCII-compatible text encoding if you can possibly avoid it  naive programs expecting ASCII tend to misinterpret them in catastrophic  often security-breaking fashion   They are so deprecated nowadays that  for instance  HTML5 forbids their use on the public Web  with the unfortunate exception of UTF-16   I m not going to talk about them any more   A fixed-width encoding means what it sounds like  all characters are encoded using the same number of bytes   To be ASCII-compatible  a fixed-with encoding must encode all its characters using only one byte  so it can have no more than 256 characters   The most common such encoding nowadays is Windows-1252  an extension of ISO 8859-1   There s only one variable-width ASCII-compatible encoding worth knowing about nowadays  but it s very important  UTF-8  which packs all of Unicode into an ASCII-compatible encoding   You really want to be using this if you can manage it   As a final note   ASCII  nowadays takes its practical definition from Unicode  not its original standard  ANSI X3 4-1968   because historically there were several dozen variations on the ASCII 127-character repertoire -- for instance  some of the punctuation might be replaced with accented letters to facilitate the transmission of French text   Nowadays all of those variations are obsolescent  and when people say  ASCII  they mean that the bytes with value 0x00 through 0x7F encode Unicode codepoints U 0000 through U 007F   This will probably only matter to you if you ever find yourself writing a technical standard   If you re interested in the history of ASCII and the encodings that preceded it  start with the paper  The Evolution of Character Codes  1874-1968   samizdat copy at http   falsedoor com doc ascii evolution-of-character-codes pdf  and then chase its references  many of which are not available online and may be hard to find even with access to a university library  I regret to say

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The original ASCII code provided 128 different characters numbered 0 to 127  ASCII a 7-bit are synonymous  since the 8-bit byte is the common storage element  ASCII leaves room for 128 additional characters which are used for foreign languages and other symbols  But 7-bit code was original made before 8-bit code  ASCII stand for American Standard Code for Information Interchange In early internet mail systems  it only supported only 7-bit ASCII codes  this was because it then could execute programs and multimedia files over suck systems  These systems use 8 bits of the byte but then it must then be turned into a 7-bit format using coding methods such as MIME  UUcoding and BinHex  This mean that the 8-bit has been converted to a 7-bit characters  which adds extra bytes to encode them

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ASCII encoding is 7-bit  but in practice  characters encoded in ASCII are not stored in groups of 7 bits  Instead  one ASCII is stored in a byte  with the MSB usually set to 0  yes  it s wasted in ASCII     You can verify this by inputting a string in the ASCII character set in a text editor  setting the encoding to ASCII  and viewing the binary hex    Aside  the use of  strictly  ASCII encoding is now uncommon  in favor of UTF-8  which does not waste the MSB mentioned above - in fact  an MSB of 1 indicates the code point is encoded with more than 1 byte

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The original ASCII table is encoded on 7 bits therefore it has 128 characters   Nowadays most readers editors use an  extended  ASCII table  from ISO 8859-1   which is encoded on 8 bits and enjoys 256 characters  including                    and other characters useful for european languages as well as mathematical glyphs and other symbols    While UTF-8 uses the same encoding as the basic ASCII table  meaning 0x41 is A in both codes   it does not share the same encoding for the  Latin Extended-A  block  Which sometimes causes weird characters to appear in words like    la carte or pi  ata

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when we call ASCII as 7 bit code  the left most bit is used as sign bit so with 7 bits we can write up to 127  that means from -126 to 127 because Max imam value of ASCII is 0 to 255  this can be only satisfied with the argument of 7 bit if last bit is considered as sign bit

[character-encoding] Is ASCII code 7-bit or 8-bit?

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