Source : Free On-Line Dictionary of Computing

Zilog Z8000
     
         A {microprocessor} from {Zilog} introduced not
        long after the {Intel 8086}, but with superior features.  It
        was basically a 16-bit processor, but could address up to 23
        bits in some versions by using {segment registers} (to supply
        the upper 7 bits).  There was also an unsegmented version, but
        both could be extended further with an additional {MMU} that
        used 64 {segment registers}.
     
        Internally, the Z8000 had sixteen 16-bit {registers}, but
        register size and use were exceedingly flexible.  The Z-8000
        registers could be used as sixteen 8-bit registers (only the
        first half were used like this), sixteen 16-bit registers,
        eight 32-bit registers, or four 64-bit registers, and included
        32-bit multiply and divide.  They were all general purpose
        registers - the {stack pointer} was typically register 15,
        with register 14 holding the stack segment (both accessed as
        one 32-bit register for painless address calculations).
     
        The Z8000 featured two modes, one for the {operating system}
        and one for user programs.  The user mode prevented the user
        from messing about with {interrupt} handling and other
        potentially dangerous stuff.
     
        Finally, like the {Zilog Z80}, the Z8000 featured automatic
        {DRAM refresh} circuitry.  Unfortunately it was somewhat slow,
        but the features generally made up for that.  Initial {bugs}
        also hindered its acceptance (partly because it did not use
        {microcode}).  There was a radiation resistant military
        version.
     
        There was a later 32-bit, {pipelined} version, the {Zilog
        Z80000}.
     
        (1997-12-16)