ASCII, symbols: description, code table and views
As you know, the computer stores information inbinary form, representing it as a sequence of ones and zeros. To translate information into a form that is convenient for human perception, each unique sequence of digits in the display is replaced by the corresponding symbol.
One of the systems of correlating binary codes with print and control characters is the ASCII encoding.
With today's level of development of computertechnology from the user does not require knowledge of the code of each specific symbol. However, a common understanding of how coding is performed is extremely useful, and for some categories of specialists it is absolutely necessary.
In its original form, the encoding was developed in 1963 and then updated for 25 years.
In the original version, the ASCII character set128 characters later, an extended version appeared, where the first 128 characters were saved, and the codes with the eighth bit involved corresponded to the missing symbols.
Over the years, this encoding has been the most popular in the world. In 2006, Latin 1252 took the leading place, and from the end of 2007 to the present time Unicode firmly holds the leading position.
Computer ASCII Presentation
Each ASCII character has its own code,consisting of 8 characters, representing a zero or one. The minimum number in this representation is zero (eight zeros in the binary system), which is the code of the first element in the table.
The maximum binary code in the original version of ASCII is zero + seven units, and in the extended version - eight units, since the eighth bit is connected.
Control characters are signs that are notThey can be used to organize text, control devices, etc. They can denote the beginning or the end of the text, tabulation, the generation of a sound signal, various operations for working on a teletype (teletype-machine for data transfer via an electrical channel), output resolution data on the device, cancel the action, etc.
In the ASCII character table positions from 0 to 31, as well as 127 are allocated for control characters. Total of such signs 33.
The remaining 95 positions are allocated for signspunctuation and signs of mathematical operations, decimal digits, letters of the Latin alphabet, distinguished by the register: "A" uppercase and "a" lowercase correspond different codes in the ASCII character table.
Numbers of symbols in the table
If a person is developing software or performing some other tasks in the field of information technology, he needs to know the numbers of a number of ASCII characters.
As mentioned above, positions 0-31 and 127 occupy control characters. Number 32 is assigned to a space, numbers 33-47 and 58-64 are assigned to punctuation marks and basic mathematical operations.
Latin capital letters are arranged in alphabetical orderand have numbers from 65th to 90th. Lowercase letters are also arranged alphabetically, their positions are from 97th to 122nd. The remaining numbers (91-96 and 123-126) are assigned to the square and curly braces, oblique and straight line, and also some diacritical marks.
A complete table of symbols in a convenient graphical representation can be seen in the image presented above. The figure below shows the character numbers in the Russian ASCII character table.
Since the original version of the encodingwas designed in the calculation of the American user, it did not provide for not only different types of writing and national alphabets, but even the convenient use of diacritic marks actively used in European languages.
To form an extended encoding,The 8th bit is involved. This version includes the symbols of the national European alphabets and phonetic transcription, the elements of graphics used for drawing tables, a number of mathematical signs.
Some ASCII characters are used todayrarely. In particular, this concerns the signs used to draw tables, since many more convenient ways of graphical representation of tables have been introduced in the years since the development of the extended encoding.
National encoding options
Before the advent of the extended version of ASCII fordisplay of national alphabets used the revised version of the encoding, where the place of the Latin letters were Russian, Greek, Arabic characters.
Two codes in the table were assigned to switch between the standard US-ASCII and its national variant.
After ASCII began to include not 128, but 256characters, the distribution received a version of the encoding, in which the original version of the table was stored in the first 128 codes with zero 8th bit. Signs of national writing were kept in the upper half of the table (128-255th position).
Know the ASCII character codes directlythe user is not required. It is usually sufficient for a software developer to know the number of an element in a table in order to calculate its code, if necessary, using a binary system.
After the development in the early 70's of codingsfor the Scandinavian languages, Chinese, Korean, Greek, etc., the creation of its own version was taken up by the Soviet Union. Soon, a version of the 8-bit encoding called KOI8 was developed, preserving the first 128 ASCII character codes and allocating as many positions for the letters of the national alphabet and additional characters.
Prior to the introduction of Unicode, KOI8 dominated the Russian segment of the Internet. There were variants of encoding for both Russian and Ukrainian alphabet.
Problems with ASCII
Since the number of elements even in the extendedthe table did not exceed 256, the possibility of containing several different scripts in one encoding was missing. In the 90s the problem of "crocosyabr" appeared in Runet, when the texts typed by Russian ASCII characters were displayed incorrectly.
The problem was the inconsistency of the codesdifferent ASCII variants to each other. Recall that at positions 128-255, different characters could be placed, and when one Cyrillic encoding changed to another, all the letters of the text were replaced by others having an identical number in another version of the encoding.
With the advent of Unicode, the popularity of ASCII has plummeted.
The reason for this lies in the fact that the new encoding allowed to contain the signs of almost all written languages. The first 128 ASCII characters correspond to the same Unicode characters.
In 2000, ASCII was the most popular encoding inInternet and was used on 60% of Google's pages indexed by Google. By 2012 the share of such pages has fallen to 17%, and the place of the most popular encoding was occupied by Unicode (utf-8).
Thus, ASCII is an important part of the history of information technology, but its use in the future is seen as unpromising.