Extended ASCII represents another 128 characters, with bit 7 set to 1.
More on ASCII.
The hex value for the letter 'D' is 44. In binary, that would be:
4416 = 010001002 = 0 + 26 + 0 + 0 + 0 + 21 + 0 + 0 = 64 + 4 = 68In decimal, 'D' is 68
27 26 25 24 23 22 21 20 0 1 0 0 0 1 0 0 = 0 + 26 + 0 + 0 + 0 + 21 + 0 + 0 = 64 + 4 = 68
First 32 characters are not printable - they are control characters.
There are 96 printable characters.
(click on picture to see another version of table)
Extended ASCII character set, high bit (bit 7) set to one. (click on picture to see another version of table)
Note that as the need to represent more characters (Chinese, Thai, Japanese) increases, we need a larger code space. This is why ASCII is being replaced by Unicode. Unicode uses 16 bits which means it can represent 2^16 = 65,536 different characters. 32 bit codes are also being considered which would allow over 4 billion characters to be represented.
As a result of the rapid development and spread of communications and data processing technologies in the United States in the first half of the 20th century, it became apparent there was a need for a standard character code for interchanging data that could handle the full character set of an English-language typewriter.
In 1963, ASA announced the American Standard Code for Information Interchange. However, ASCII as it was announced in 1963 left many positions, such as those for the lower case Latin letters, unallocated. It wasn't until 1968 that the currently used ASCII standard of 32 control characters and 96 printing characters was defined.
Reference: Brief History of Character Codes ...