Question about translation units

[RAMontante]

Hello,

Could someone please tell me how to determine the extent of a `translation
unit'?  Some things described in K&R2 have a scope or linkage of one
translation unit, extern declarations and definitions in particular.
Apparently some Unix implementations extend the linkage to the entire
program...?

Email replies preferred, I'll summarize if it seems warranted,

thanks.
bob,mon.