The intent here is to allow Racket CS to run on any platform where Racket BC runs — including platforms where Racket CS has no machine-code backend, which is a subset of platforms where Racket BC has no JIT. Run time for Racket code in CS without a machine-code backend is similar to run time in BC without a JIT, although compilation times are still slower in the CS variant (because the Racket BC bytecode compler is implemented directly in C, instead of compiled from Scheme to "portable bytecode" to C).
Here's a suggested rewording to say more:
- Racket CS runs on platforms where native-code generation is not currently supported (e.g., s390x or ppc64). See "README.txt" in the source distribution for more information on the
--enable-pbflag toconfigure.