The Quadra 700 and 900 introduced the 68040 in 1991. In great part due to a much larger L1 cache (4 KB for data and 4 KB for instructions vs. 256 bytes in the 68030) and parts of the CPU running at twice clock speed, the 68040 provides 2.5-3 times the performance of the 68030 at the same clock speed.

The regular 68040 includes its own FPU (floating point unit or math coprocessor), which had been a separate chip with the 68020 and 68030. The FPU is missing in the less expensive 68LC040 used in some low-end Macs.

The slowest model based on the 68040 was the Centris 610, which has a 20 MHz 68LC040. The fastest was the 40 MHz Quadra 840av (right).

Because it has such a large L1 cache, none of the 68040-based Macs shipped with with a L2 cache, although some 128 KB cards were offered by other manufacturers. As with L2 cards on the Mac IIci, these provide a 20-30% performance boost.

The next chip in the 68000 family was the 68060, a wicked fast CPU with architectural features similar to Intel’s Pentium. However, Apple decided to move in a different direction, and the ‘060 only made its way into one Amiga computer (the A4000T), some Amiga accelerators, and some Alpha computers. With such a small market, the ‘060 marked the end of the 68000 family.

After looking at the Motorola 88000 and even building some prototypes, Apple decided to team up with Motorola and IBM to create a new CPU family. Future Macs would use PowerPC CPUs.

Motorola 680×0 Family Overview

CPU       speed*      L1 cache     FPU**    notes
68000     8-16 MHz          none      none  16-bit data bus, 24-bit addressing
68020       16 MHz     256 bytes     68881
68030    16-40 MHz   2x256 bytes     68882  internal PMMU, supports L2 cache
68LC040  20-25 MHz  2x4096 bytes      none  can be replaced with 68040
68040    25-40 MHz  2x4096 bytes  internal
68060    50-75 MHz  2x8192 bytes  internal
__________
* as used in Apple computers
** FPU typically used with this CPU

Motorola CPUs: 68000, 68020, 68030, 68040, 68060

Other Resources

• Great CPUs, past and present, John Bayko. See especially sections on 8080/85, Z-80, 6502, 6809, 680×0, 80×86, ARM (used in Newton), PA-RISC, Sparc, Alpha, PowerPC, and Merced.
• MacTips, RISC, CISC, and Your Mac
• PC Magazine, Motorola and PowerPC (also covers 680×0 series)
• Pipelines, MHz, latency, caches, and more, MacKiDo

Keywords: #motorola68040 #motorolacpus

Short link: http://goo.gl/BN7YU7

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