32 bit and high core count is definitely a nasty combo. Many applications spawn 2-4 threads per core which is a great way to eat up that address space.
But don't all threads of a process share mostly the same address space?
I could imagine that starting many processes would exhaust address space, or allocating a lot of virtual memory / mmap without committing.
That's one of the fun bits, other processes don't share the memory space. That's one reason you can have 16GiB of ram on a 32bit x86 server without much issue. This was done on x86 through a tech called PAE (Physical Address Extension) that let the OS know there was more memory and allocate it around, but any one process was limited to 4GiB (usually lower due to kernel/userspace barriers) because of 32 bit pointers. So if those threads all allocated memory it was easier to hit the limit but if you used separate processes then they could each reach 4GiB (or whatever the limit is) independently without causing problems.
