On Tue, Jun 05, 2007 at 03:30:47PM -0700, Christopher Cramer wrote:
> If the fork had to copy the entire process image before just
> throwing it away upon exec, I think Unix, which is based around a
> philosophy of piping between multiple processes, would have
> abandoned fork a long time ago. Then again, there is vfork, so I
> guess they almost did abandon it at one point.

vfork was introduced in BSD Unix when support for page-based virtual
memory was added for the DEC VAX.  There was an earlier Bell Labs
port of Unix to the VAX that just mimicked the PDP-11's segment
registers.  In that scheme, I believe text segments were shared, so
that only the data segment had to be copied on fork, but copy-on-write
is the way to go on any architecture with page tables.

-- 
Eric Cooper             e c c @ c m u . e d u