I think you guys are both right. Back in the days when I measured UNIX performance, it was fork that was expensive due to memory allocation - but not the memory

I think you guys are both right. Back in the days when I measured UNIX performance, it was fork that was expensive due to memory allocation - but not the memory itself. It takes time to allocate all the page tables associated with the memory when you are setting up for the context switch. But I should admit that it was a long time ago that I traced that code path.