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The 68040 is the first 680x0 family member with an on-chip FPU (floating point unit). It thus includes all of the functionality that previously required external chips, namely the FPU and MMU (which was added in the 030). It also has split instruction and data caches of 4 kilobytes each. It is fully pipelined, with six stages.

Unfortunately the '040 ran into the transistor budget limit early in design. While the MMU did not take many transistors (indeed, having it on the same die as the CPU actually saved on transistors) the FPU certainly did. Motorola's 68882 external FPU was known as a very high performance unit and Motorola did not wish to risk integrators using the "LC" version with a 68882 rather than the more profitable full "RC" unit. For information on Motorola's multiprocessing model with the 680x0 series, see 68020. The FPU in the 68040 was thus made incapable of IEEE transcendental functions, which had been supported by both the 68881 and 68882 and were used by the popular fractal generating software of the time and little else. The Motorola floating point support package (FPSP) emulated these instructions in software under interrupt. As this was an exception handler, over-use of the transcendental functions caused severe performance penalties.

Heat was always a problem throughout the 68040's life. While it delivered over double the per-clock performance of the old-when-released 68030 the chip's complexity and power requirements came from a large die and large caches. This affected the scaling of the processor and it never made it past 40MHz. A 50MHz variant was planned, but scrapped. Proto-overclockers reported success using the then-hardcore heatsinks with fans. The 68040 was feature-parity with the Intel 80486 but outperformed it quite significantly on a clock for clock basis.

Versions of the '040' were created for specific market segments, including the 68LC040 which removed the FPU, and the 68EC040 which removed both the FPU and MMU. Various versions were used in the Amiga and Apple Macintosh Quadra series of personal computers, as well as being used in a number of Workstations and later versions of the NeXTThe NeXT logo, designed by Paul Rand. NeXT was a computer company, known to the public for its series of futuristic computers, and to the programming world for its development platforms. It was bought in a takeover by Apple Computer and is no longer in bu computers.

For more information on the instructions and architecture, see Motorola 68000The Motorola 68000 is a CISC microprocessor, the first member of a successful family of microprocessors from Motorola, which were all mostly software compatible. The entire series was often referred to as the m68k or simply 68k History Originally, the MC6.

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