ASCII or EBCDIC?

Date: 05/11/2002 at 22:31:20
From: Lynn
Subject: ASCII or EBCDIC?

I am studying about magnetic disks.  I understand about magnetized 
spots equaling 1's and spaces equaling 0's.  But the problem I have 
asks whether 01000001 is equal to an ASCII 0 or A or an EBCDIC A or B. 

I have spent part of 2 days trying to get an answer but so far nothing
that equals these choices.  Can you help me understand how to do the
math?

Date: 05/12/2002 at 03:02:07
From: Doctor Jeremiah
Subject: Re: ASCII or EBCDIC?

Hi Lynn,

ASCII and EBCDIC are completely different ways of interpreting
a given sequence of bits.  When you have something that is a 
valid interpretation in multiple encodings, then without knowing 
what the data is supposed to be and without knowing what the 
encoding was there is no way to guess.

(Note that there is only one ASCII encoding; but there are several
variants of EBCDIC.)

And there are some characters that are valid in both encodings.
Fortunately 01000001 (which is hex 41) is not one of them.  It has no
meaning in EBCDIC, but its meaning in ASCII is 'A'.  

Knowing that the tape is ASCII allows you to interpret all the other
values that might cause problems.

Here are a couple web pages I found that tell you what
characters belong to which binary values:

  http://www.egrannie.com/cheatsheets/asciiebcdic.html 
  http://www.natural-innovations.com/boo/asciiebcdic.html 
  http://www.simotime.com/asc2ebc1.htm 

Hope this helps. 

- Doctor Jeremiah, The Math Forum
  http://mathforum.org/dr.math/