Bits, Bytes, and Unicode

July, 2018
What is ASCII, UTF-8, and Unicode


A bit is the smallest unit in computing. It is either a 1 or a 0 . Next up is a byte, a byte is 8 bits. 256 (2^8) patterns can be represented by a byte. One byte can store the numbers 0 through 255 in decimal notation. The number 255 is 11111111 and is 8 bits, one byte in length.


ASCII (American Standard Code for Information Interchange) is the first encoding standard. It is able to represent 128 characters. This is because ASCII uses a 7-bit encoding. It contains the English letters A-Za-z, numbers 0-9, and some special characters as well. So a single byte is able to store an ASCII character. HTML 4.0 defaulted to ASCII.


UTF-8 (Unicode Transformation Format) is backwards compatible with ASCII. It essentially takes the 7-bit ASCII encoding and expands it with more bits, and is thus able to represent more characters. UTF-8 characters can be from 1 to 4 bytes long. So UTF-8 uses a 16-bit encoding. It is capable of representing all of Unicode with the ability to represent 2^21 characters. HTML5 defaults to using UTF-8.


Unicode is a character set that represents almost all the characters in the world.


Encoding is how the characters are translated into bits. It’s the 1 and 0 representation.

Encoding translates numbers into binary. Character sets translates characters to numbers.

The decimal representation of the character ‘A’ in ASCII is A . When the character ‘A’ is written to disk it is stored in bits 0s and 1s in a single byte that is the binary number 65, 01000001.

It is important to understand the relationship between encoding and character sets.

The ‘8’ in UTF-8 refers to the fact that 8 is the minimum number of bits required to store a character. Remember UTF-8 uses 1-4 bytes.