extern globals and procedures

[Ted Lowery]

All-

I notice in most of the sample code, every global variable and
function/procedure is declared extern.  I'm not used to coding like this,
and thus far I have NOT been declaring my code segments extern.  Is this ok,
or will it break in future OSs?  What is extern really doing in the sample
code?  It seems unnecessary for a single segment program.

Thanks, Ted
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