Also, don't run Linux on those machines, but their native OS: Solaris, AIX, HP/UX respectively.
uhh...what is advantage of running System P with AIX over System X with RHEL in terms of security? I really don't get this.)
safety exists naturally not
lol? we are in 2015 my friend, security is just about amount of money (human effort), which you want to invest..HW tokens, DMZ clusters, reverse proxy, T4 DC with all security measurements, locked cabinet...omfg. just money..