50 Percent, 128 out of 256
The chart for ASCII shows all possible 7-bit patterns. There are twice as many 8-bit patterns. Some computer makers use the additional patterns to represent various things. Old MS Windows PCs, for example, used these extra patterns to represent symbols and graphics characters. Some printers will not work with these additional patterns.
Part of what an assembler does is to assemble the ASCII bit patterns that you have asked to be placed in memory. Here is a section of an assembly language program:
.asciiz "ABC abc"
Here are the bit patterns that the assembler will produce in the object module:
41 42 43 20 61 62 63 00
The .asciiz part of the source code asked the assembler to assemble the characters between the quote marks into ASCII bit patterns. The first character, "A", corresponds to the bit pattern 0x41. The second character, "B", corresponds to the bit pattern 0x42. The fourth character, " " (space), corresponds to the bit pattern 0x20. The final bit pattern 0x00 (NUL) is used by the assembler to show the end of the string of characters.
What will be the assembled patterns for this assembly code:
.asciiz "A B"