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Digression #2: ASCII Text
Fundamental idea: the most basic unit of data is the
byte -- virtually all computers (and network systems)
handle data one byte at a time. Recall that a byte is an 8-bit
value and thus can take any value between zero and
255decimal.
US-ASCII (or, just "ASCII") was the first widely accepted data
representation system, and is universally recognised. In its
traditional form, it's a 7-bit code, meaning that if an ASCII
message is stored or carried in a modern byte-oriented system, the
Most Significant Bit (MSB) of every byte will
always be zero. For this reason, ASCII messages are sometimes
called "7-bit data". An ASCII-valued byte has traditionally been
called a "character", and obviously takes any value between zero
and 127.
Within the ASCII "character set" there is a further
subdivision:
- Printable ASCII
- characters with values between 32 (the ASCII "space" character)
and 127 (the "DEL" character). This includes all of the uppercase
and lowercase letters, the digits and the punctuation
characters.
- Control Characters
- character values between zero and 31. These were originally
designed for a range of "official functions", most of which are now
irrelevant.
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