资料来源 : Free On-Line Dictionary of Computing

Motorola 68000
     
         (MC68000) The first member of {Motorola, Inc.}'s
        family of 16- and 32-bit {microprocessors}.  The successor to
        the {Motorola 6809} and followed by the {Motorola 68010}.
     
        The 68000 has 32-bit registers but only a 16-bit {ALU} and
        external {data bus}.  It has 24-bit addressing and a {linear
        address space}, with none of the evil {segment registers} of
        {Intel}'s contemporary processors that make programming them
        unpleasant.  That means that a single directly accessed
        {array} or structure can be larger than 64KB in size.
        Addresses are computed as 32 bit, but the top 8 bits are cut
        to fit the address bus into a 64-pin package (address and data
        share a bus in the 40 pin packages of the {8086} and {Zilog
        Z8000}).
     
        The 68000 has sixteen 32-bit {registers}, split into data and
        address registers.  One address register is reserved for the
        {Stack Pointer}.  Any register, of either type, can be used
        for any function except direct addressing.  Only address
        registers can be used as the source of an address, but data
        registers can provide the offset from an address.
     
        Like the {Zilog Z8000}, the 68000 features a supervisor and
        user mode, each with its own {Stack Pointer}.  The {Zilog
        Z8000} and 68000 are similar in capabilities, but the 68000 is
        32 bits internally, making it faster and eliminating forced
        segmentations.
     
        Like many other CPUs of its generation, it can fetch the next
        instruction during execution (2 stage {pipeline}).
     
        The 68000 was used in many {workstations}, notably early
        {Sun-2} machines, and {personal computers}, notably {Apple
        Computer}'s first {Macintoshes} and the {Amiga}.  It was also
        used in most of {Sega}'s early arcade machines, and in the
        {Genesis}/{Megadrive} consoles.
     
        Variants of the 68000 include the {68HC000} (a low-power HCMOS
        implementation) and the {68008} (an eight-bit data bus version
        used in the {Sinclair QL}).
     
        ["The 68000: Principles and Programming", Leo Scanlon, 1981].
     
        (2003-07-11)