Motorola 68000 - meaning and definition. What is Motorola 68000
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What (who) is Motorola 68000 - definition

MC68000; 68000; M68000; 68000 Microprocessor; 68000 processor archictecture; Motorola MC68000; Motorola 68EC000; 68ec000; Motorola MC68EC000; MC68HC000; MACSS; Motorola 68HC000; Motorola 68000 microprocessor; Motorola 68000 processor; Motorola 68SEC000
  • [[Hitachi]] HD68000
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  • Thomson TS68000
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  • Motorola MC68HC000LC8
  • Motorola MC68000 ([[plastic leaded chip carrier]] (PLCC) package)
  • Pre-release XC68000 chip made in 1979

Motorola 68000         
<processor> (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)


Motorola 68000

The Motorola 68000 (sometimes shortened to Motorola 68k or m68k and usually pronounced "sixty-eight-thousand") is a 16/32-bit complex instruction set computer (CISC) microprocessor, introduced in 1979 by Motorola Semiconductor Products Sector.

The design implements a 32-bit instruction set, with 32-bit registers and a 16-bit internal data bus. The address bus is 24 bits and does not use memory segmentation, which made it easier to program for. Internally, it uses a 16-bit data arithmetic logic unit (ALU) and two more 16-bit ALUs used mostly for addresses, and has a 16-bit external data bus. For this reason, Motorola termed it a 16/32-bit processor.

As one of the first widely available processors with a 32-bit instruction set, large unsegmented address space, and relatively high speed for the era, the 68k was a popular design through the 1980s. It was widely used in a new generation of personal computers with graphical user interfaces, including the Macintosh 128K, Amiga, Atari ST, and X68000. The 1988 Sega Genesis/Mega Drive console is powered by a 68000.

Later processors in the Motorola 68000 series, beginning with the Motorola 68020, use full 32-bit ALUs and have full 32-bit address and data buses. The original 68k is generally software forward-compatible with the rest of the line despite being limited to a 16-bit wide external bus.

After 44 years in production, the 68000 architecture is still in use.

Examples of use of Motorola 68000
1. In the early 1''0s, it moved from Motorola 68000 chips to the PowerPC architecture.
2. He pointed to Apple‘s move from its original Motorola 68000–based systems to systems using the Power PC.