Comment by guerrilla

Back then there were quite a few competing architectures and UNIXes to go with them. SGI MIPS with Irix, IBM had POWER with AIX and later Linux, DEC had Alpha Tru64 UNIX and VMS (not a UNIX), Sun SPARC with Solaris, HP had HA-RISC with HP-UX. Only SPARC and POWER survived for long and only POWER survived until today as far as I know. Solaris of course lives on in various forms. The old UNIXes I guess mostly do not, being displaced almost entirely by Linux and BSDs.