Motorola 68040

The Motorola 68040, also referred to as the 68040 or '040, is a 32-bit processor that was produced by Motorola's Semiconductor Products Sector, superseding the Motorola 68030. The 68040 was used in the Centris, Quadra, and PowerBook 500 series. It was also used in the NeXTcube and NeXTstation computers. It was the last of the 68k processor series to be used by Apple Computer, which migrated to PowerPC processors for its Power Macintosh line.

Features
Introduced in 1990, the 68040 improved processor performance over the 68030 by increasing the instruction and data caches eight-fold to 4 kilobytes each. was doubled to 6 stages. However, the was known to break some older hard-coded software. This could be turned off with a software cache switch for the sake of backward compatibility, but at the expense of a 3-fold penalty in performance.

Internal units operated at twice the speed of the external clock, so Apple and other companies sometimes marketed their 68040-based products with two clock speeds, such as 66/33MHz.

The 68040 was available in external clock speeds up to 40MHz in a ceramic (PGA) package. However, heat became a factor in the design and a 50MHz version was cancelled. The compact (QFP) version was delayed for Apple's PowerBook 500 series and limited to 33MHz.

Variants

 * Motorola 68LC040 - a low-cost version without a built-in floating-point unit. Mostly used in entry-level and portable Macintosh models. Units with mask numbers lower than 03E23G (manufactured before late 1994) contain a bug which breaks software emulating a floating-point unit, such as SoftwareFPU. These defective units were found in many early Macintosh LC 475s and Quadra 605s. Patrick Fleming of Apple Computer reportedly denied the existence of the bug, but Motorola confirmed it as bug E4 in revision 4 of their official 68LC040 errata sheet.
 * Motorola 68EC040 - a lower-cost embedded version without built-in floating-point nor s. Not used by Apple in any model.