Computers usually store ASCII text as one character per byte. A byte can store values 0 to 255, but ASCII codes only use values 0 to 127. This means that the codes 128 to 255 are unused.
Extended ASCII makes us of these unused codes to define extra characters.
Latin1 Extended ASCII (also called ISO/IEC 8859-1) includes all the common accented characters used by European languages, as well as extra currency symbols and various other punctuation. This standard is used by Windows as the default extended character set, and is also used for the first block of Unicode characters.
Here is the table (values 128 to 159 are not used):
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