The Racket runtime system is responsible for the implementation of primitive datatypes such as numbers and strings, the macro expansion and compilation of Racket from source, the allocation and reclamation of memory used during evaluation, and the scheduling of concurrent threads and parallel tasks.
This manual describes the C interface of Racket’s runtime system, which varies depending on the implementation of Racket (see Racket Virtual Machine Implementations): the CS implementation of Racket has one interface, while the BC (3m and CGC) implementation of Racket has another.
The C interface is relevant to some degree when interacting with foreign libraries as described in The Racket Foreign Interface. Even though interactions with foreign code are constructed in pure Racket using the ffi/unsafe module, many details of representations, memory management, and concurrency are described here. This manual also describes embedding the Racket run-time system in larger programs and extending Racket directly with C-implemented libraries.