 In GNU Emacs, primitives are not available as external libraries; they are part of the Emacs executable.In XEmacs, runtime loading of such primitives is possible, using the operating system's support for dynamic linking.Functions may be written as primitives because they need access to external data and libraries not otherwise available from Emacs Lisp, or because they are called often enough that the comparative speed of C versus Emacs Lisp makes a worthwhile difference.