As you know, a computer stores information in binary form, representing it as a sequence of ones and zeros. In order to translate the information into a form convenient for human perception, each unique sequence of digits when displayed is replaced with the corresponding symbol.
One of the systems of correlation of binary codes with printed and control characters is ASCII coding.
At the current level of computer technology, the user is not required to know the code of each specific character. However, a common understanding of how coding is carried out is extremely useful, and even necessary for some categories of specialists.
ASCII creation
In its original form, the encoding was developed in 1963 and then twice over the course of 25 years.
In the original version, the ASCII character table included 128 characters, later an extended version appeared, where the first 128 characters were saved, and codes with the eighth bit involved were mapped to previously missing characters.
Over the years, this encoding has been the most popular in the world. In 2006, Latin 1252 took the lead, and from the end of 2007 to the present, Unicode has held the leading position.
ASCII Computer View
Each ASCII character has its own code, consisting of 8 characters, representing 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 advanced version - eight units, since the eighth bit is connected.
Control characters
Control characters are signs that do not have a graphical representation and are used to organize text, control devices, etc. They can indicate the beginning or end of a text, tabs, generate a sound signal, various operations for working on a teletype (teletype is a machine for transmitting data via electrical channel), permission to output data on the device, cancellation of actions, etc.
In the ASCII character table, positions 0 through 31 and 127 are highlighted as control characters. There are 33 such signs.
Other characters
The remaining 95 positions are reserved for punctuation marks and signs of mathematical operations, decimal digits, letters of the Latin alphabet, differing in case: βAβ uppercase and βaβ lowercase correspond to different codes in the ASCII character table.
Character numbers in the table
If a person is engaged in software development or performs 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 are held by control characters. Number 32 is assigned to a space, numbers 33-47 and 58-64 are reserved for punctuation marks and basic mathematical operations.
Latin capital letters are arranged alphabetically and have numbers from the 65th to the 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 square and curly brackets, a slash and a straight line, as well as some diacritical marks.
A complete table of characters in a convenient graphical representation can be seen in the image above. The figure below shows the character numbers in the Russian ASCII character table.
Extended ASCII
Since the original version of the encoding was designed for the American user, it did not provide for not only various types of writing and national alphabets, but even convenient use of diacritics, which are actively used in European languages.
The 8th bit was used to form the extended encoding. This version includes symbols of national European alphabets and phonetic transcription, graphic elements used to draw tables, a number of mathematical signs.
Some ASCII characters are rarely used today. In particular, this applies to characters used to draw tables, since over the years that have passed since the development of the advanced encoding, much more convenient ways of graphical presentation of tables have been introduced.
National Encoding Options
Before the extended version of ASCII appeared, for the display of national alphabets, processed versions of the encoding were used, where Russian, Greek, Arabic characters were located in place of Latin letters .
Two codes in the table were reserved for switching between standard US-ASCII and its national version.
After ASCII began to include not 128, but 256 characters, the encoding option was spread, in which the original version of the table was stored in the first 128 codes with a zero 8th bit. Signs of national writing were stored in the upper half of the table (128-255th position).
The user does not need to know the ASCII character codes directly. 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.
Russian language
After the development of encodings for the Scandinavian languages, Chinese, Korean, Greek, etc. in the early 70s, the Soviet Union also began to create its own version. Soon, an 8-bit encoding option was developed under the name KOI8, which stores the first 128 ASCII character codes and allocates the same number of positions under 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 encoding options for both the Russian and Ukrainian alphabets.
ASCII problems
Since the number of elements, even in the extended table, did not exceed 256, there was no possibility of containing several different scripts in one encoding. In the 90s, the Run-of-the-Road problem appeared in Runet when texts typed in Russian ASCII characters were displayed incorrectly.
The problem was that the codes for the various ASCII variants did not match. Recall that at positions 128-255 different characters could be located, and when changing one Cyrillic encoding to another, all letters of the text were replaced with other letters that have the same number in another version of the encoding.
Current state
With the advent of Unicode, ASCII's popularity plummeted.
The reason for this lies in the fact that the new encoding allowed the characters of almost all written languages ββto be accommodated. In this case, the first 128 characters of ASCII correspond to the same characters in Unicode.
In 2000, ASCII was the most popular encoding on the Internet and was used on 60% of Google-indexed web pages. By 2012, the share of such pages fell to 17%, and Unicode (UTF-8) took the place of the most popular encoding.
Thus, ASCII is an important part of the history of information technology, but its use in the future is seen as unpromising.