"Unix systems" is a kind of antiquated term for when the big iron vendors (IBM, Sun, HP, DEC, MIPS) sold large RISC systems with the hardware (Power, SPARC, pa-risc, Alpha, MIPS) as a loss leader for the proprietary UNIX (AIX, Solaris, HPUX, Tru64, RiscOS) running on them. Linux ate most of those proprietary unices, and now the economic logic (for the remaining survivors) is reversed: the money is in the hardware and in support.