I would suspect that it IS multiple boxes and with z/VM using single system image. This is the first time I've ever heard of mainframe "in a rack". In the past

I would suspect that it IS multiple boxes and with z/VM using single system image. This is the first time I've ever heard of mainframe "in a rack". In the past they come in their own cabinet, but if you open the cabinet door you won't see one "box".