how does nix know what binary a machine needs? -

they write in nix documentation:

however, nix can automatically skip building source , instead use binary cache, web server provides pre-built binaries. instance, when asked build /nix/store/b6gvzjyb2pg0…-firefox-33.1 source, nix first check if file https://cache.nixos.org/b6gvzjyb2pg0….narinfo exists, , if so, fetch pre-built binary referenced there; otherwise, fall building source.

i wonder how nix know kind of binary machine needs? if ran nix on arm or intel or amd or name it. how binaries cache selected right architecture?

nix purely functional package manager. such takes package needs input function, including called stdenv, contains information architecture.

using these inputs nix generates hash. see in front of package name.

so architecture needed encoded in hash, why when downloading binary cache hash needs checked.