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 for Motorola 68000
From The Free On-line Dictionary of Computing (30 December 2018) :

  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
     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
     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">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].

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