fork() doesn't actually copy entire pages of memory. But it does have to copy the page tables (note - someone else might be able to chip in and tell me that Lin

fork() doesn't actually copy entire pages of memory. But it does have to copy the page tables (note - someone else might be able to chip in and tell me that Linux has an optimisation for that too). The actual pages are held with a copy-on-write status, so they won't be copied until they are actually modified by one of the processes. There are quite a lot of things that survive exec(). Not least of which is the set of open files. This is how a shell will pass on the definitions of stdin/stdout/stderr to a command that you want it to run, for example. Also, environment variables survive exec().