The ASCII code encodes char­ac­ters to specify their rep­res­ent­a­tion by elec­tron­ic devices such as PCs. For this purpose, the in­di­vidu­al char­ac­ters are converted into binary, decimal, and hexa­decim­al values that the computer can process.

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What is ASCII?

ASCII is a standard for the rep­res­ent­a­tion of char­ac­ters by elec­tron­ic devices. To get a better un­der­stand­ing of what this means it helps to be aware of how a computer works in the first place. In a computer, computing processes are always based on the binary system. That means: ones and zeros determine the processes of a computer. ASCII too is based on this system. The original ASCII standard defines different char­ac­ters within seven bits – that is, seven digits showing either a 0 or a 1.

Defin­i­tion

Character encoding is the American Standard Code for In­form­a­tion In­ter­change, and is the US precursor to ISO 646 (in­ter­na­tion­ally defined character sets). ASCII is a 7-bit code, meaning that 128 char­ac­ters (27) are defined. The code consists of 33 non-printable and 95 printable char­ac­ters and includes both letters, punc­tu­ation marks, numbers, and control char­ac­ters.

The eighth bit, which is one full byte, is tra­di­tion­ally used for checking purposes. The ASCII-based extended versions use this exact bit to extend the available char­ac­ters to 256 (28).

Fact

The original purpose of the eighth is to check the data for errors. The ‘parity’ bit allows the bit sequence receiver to detect in­con­sist­en­cies. However, the only visible aspect is what occurred, not the cause of the error. This makes the parity check fairly un­suit­able for cor­rect­ing errors.

Each character cor­res­ponds to a seven-digit sequence of zeroes and ones, which can then be rep­res­en­ted as a decimal number, or as a hexadez­i­m­al number. The ASCII char­ac­ters can be divided into several groups.

  • Control Char­ac­ters (0–31 & 127): Control char­ac­ters are not printable char­ac­ters. They are used to send commands to the PC or the printer and are based on telex tech­no­logy. With these char­ac­ters, you can set line breaks or tabs. Today, they are mostly out of use.
  • Special Char­ac­ters (32–47 / 58–64 / 91–96 / 123–126): Special char­ac­ters include all printable char­ac­ters that are neither letters nor numbers. These include punc­tu­ation or technical, math­em­at­ic­al char­ac­ters. ASCII also includes the space (a non-visible but printable character), and therefore, does not belong to the control char­ac­ters category, as one might suspect.
  • Numbers (30–39): These numbers include the ten Arabic numerals from 0-9.
  • Letters (65–90 / 97–122): Letters are divided into two blocks, with the first group con­tain­ing the uppercase letters and the second group con­tain­ing the lowercase.
Tip

To convert char­ac­ters to ASCII code ef­fort­lessly, it’s worth con­sult­ing the ASCII table, which contains the binary, decimal, and hexa­decim­al values for each character.

Example: ASCII codes

In ASCII, the system converts binary numbers into printable and non-printable char­ac­ters according to a specified standard.

If you take a look at the ASCII table, you’ll find the char­ac­ters rep­res­en­ted for various numeric values.

Example:

The binary number 01000001 can be written decimally as 65, hexa­decim­ally as 41. The character encoded with this number is an ‘A’. If you now count down further, you will find the uppercase letters listed in al­pha­bet­ic­al order. So, the word ‘ASCII’ would cor­res­pond to the following numerical values:

  A S C I I
binary 01000001 01010011 01000011 01001001 01001001
decimal 65 83 67 73 73
hexa­decim­al 41 53 43 49 49
Tip

Using Windows, you can enter Unicode char­ac­ters – thus, ASCII char­ac­ters – using a key com­bin­a­tion. To do this, hold down the Alt key and enter the decimal value of the character using the number pad on the keyboard.

ASCII code: benefits and areas of ap­plic­a­tion

ASCII is still widely used today, even though UTF-8 has become more important when present­ing a text. However, Unicode has only been dis­pla­cing the old character encoding method used during the early days of the internet since 2008. The advantage of using UTF-8 is that the code is almost back­wardly com­pat­ible: ASCII is a subset of UTF-8, so the first 128 char­ac­ters are identical. Since ASCII can be con­sidered the lowest common de­nom­in­at­or of most new encoding forms, the old encoding method is still used in emails and URLs.

Fact

Users can now use Unicode when creating emails and even domains can use umlauts thanks to In­ter­na­tion­al­ised Domain Names. However, in both cases, text must be converted to ASCII before trans­mis­sion. This is usually done auto­mat­ic­ally and users won’t notice anything.

In addition, ASCII has long been used for artistic purposes as well as technical ones: ASCII art uses ex­clus­ively printable ASCII code char­ac­ters to produce creative works. The spectrum ranges from lettering, to simple stick figures, to real paintings. ASCII artists use the different bright­ness levels of in­di­vidu­al char­ac­ters to create light and shade in their artworks.

Brief history of ASCII codes

The American Standards As­so­ci­ation (ASA, now known as ANSI for ‘American National Standards Institute’) approved the American Standard Code for In­form­a­tion In­ter­change (ASCII) back in 1963. This set out binding spe­cific­a­tion for how elec­tron­ic devices should represent char­ac­ters. Since the standard is US-American, it is often referred to as US ASCII.

Its pre­de­cessors include Morse code and the codes used in telexes, where a stand­ard­ised code (e.g. a fixed sequence of acoustic signals) is trans­lated into text. Since computers cannot handle our alphabet, because their internal processes are based on the binary system, ASCII was in­tro­duced.

To this day, the standard has rarely been changed to adapt to new re­quire­ments. For example, extended versions exist that use an eighth bit so that national pe­cu­li­ar­it­ies such as the German umlauts (ä, ö and ü) can be rep­res­en­ted. Latin-1 (ISO 88591-1), which is still popular in Germany, is based on the ASCII code.

However, it is still not possible to switch between the Latin alphabet and, for example, Arabic char­ac­ters. To this end character sets based largely on Unicode, such as UTF-8, are now well-es­tab­lished. Unicode provides space for more than a million different char­ac­ters. UTF-8 is also com­pat­ible with ASCII, encoding the first 128 char­ac­ters in the same way.

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