Explain fork() and exec() system calls and their relationship.

fork() creates a new process by duplicating the calling process - child gets copy of parent's memory (copy-on-write optimization), file descriptors, but new PID. Returns child PID to parent, 0 to child. exec() family replaces current process image with new program - same PID but new code/data. Common pattern: fork() then exec() to run new program. Parent can wait() for child completion. This separation allows child to set up (redirects, pipes) before exec.