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### What is ASCII?

```
Date: 12/19/2000 at 22:59:50
From: Monique
Subject: ASCII

I am converting binary numbers to ASCII and I don't really know what
ASCII is. Can you tell me, please?

Thank you.
```

```
Date: 12/20/2000 at 13:33:59
From: Doctor TWE
Subject: Re: ASCII

Hi Monique - thanks for writing to Dr. Math.

ASCII is an acronym (an abbreviation that's pronounced like a word)
that stands for the American Standard Code for Information
Interchange. It is not a way of representing numbers, but rather a way
of representing alpha-numeric information (text) in binary. Most
computers today use ASCII, or some extension of it, for storing and
transmitting text-based data.

Standard ASCII uses 7 bits to represent each character. But since only
2^7 = 128 different characters can be represented this way, some
computers have developed "extended ASCII" codes that use 8 (or more)
bits per character, thus allowing more characters in the character
set. The "IBM PC Extended Character Set" used in PCs is an example of
an extended ASCII code.

As an example of ASCII, here is how "Dr. TWE" would be represented in
ASCII:

char.   ASCII (binary)   Hex   Dec
-----   --------------   ---   ---
D        100 0100      44     68
r        111 0010      72    114
.        010 1110      2E     46
space      010 0000      20     32
T        101 0100      54     84
W        101 0111      57     87
E        100 0101      45     37

In the chart above, I have represented the ASCII codes in binary, as
the computer would represent them. Since writing ASCII codes in binary
requires a lot of space (and is prone to errors), we often use
hexadecimal or decimal as a "shorthand" notation. I have included the
hex and decimal equivalents on the chart above.

For a complete chart of standard ASCII, see "Standard ASCII Chart" at:

http://distance_ed.avc.edu/avcoll/faculty/ebeyer/CA103/StandardASCII_Chart.htm

Since most computers use 8 bits to represent a character, this chart
adds a space (a 0) at the beginning of each character to "fill out"
the 8 bits.

For a chart of the IBM PC Extended Character Set, see "The IBM (DOS)
Extended ASCII Character Set" at:

http://www.sageservices.bc.ca/ascii-codes.html

For information on converting among binary, hexadecimal and decimal
see our "Number Bases" FAQ page at:

http://mathforum.org/dr.math/faq/faq.bases.html

I hope this helps. If you have any more questions, write back.

- Doctor TWE, The Math Forum
http://mathforum.org/dr.math/
```
Associated Topics:
High School Calculators, Computers

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