Using a fork() system call, followed by an exec() system call is the common way to spawn a sub-process from an application. The fork() call makes a copy of the entire parent process’ address space, thus requiring two times the memory used by the parent process.

Solaris 10, provides the posix_spawn(3C) API for an application with large memory requirements to create a subprocess without running out of memory or creating a deadlock. Read more here.