Similar yes, but the difference is how they share memory. Threads, by definition, share memory so that changing a variable in one thread changes the the same variable in all other threads of that process.
I'm not sure where you're getting this, but the perl threads, at least in 5.8, aren't shared by default. Every process gets it's own copy of all of the variables and such, unless you explicitly share them.

In reply to Re^5: What is PERL_COPY_ON_WRITE Compile Option About by BUU
in thread What is PERL_COPY_ON_WRITE Compile Option About by DeadPoet

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