What is the origin of the prepended underscore?

[Jeff Glover]

Why is an underscore commonly prepended to symbols generated by most C
compilers?  Is it archaic, or is there a good reason?  I know library
writers sometimes manually prepend an underscore to hide functions from
casual users, but that is not what I am referring to.

I was asked this question, and was unable to find a satisfactory answer.

Please mail your replies, and I'll summarize for the net.
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Jeff C. Glover, Tektronix, Inc. PO Box 500, MS Y6-546, Beaverton, OR 97077
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