Apple introduced the Mac IIx, which has a 16 MHz 68030 CPU, in September 1988. The 68030 incorporates the memory management unit (MMU), which was a separate chip for the 68020, giving the ‘030 the ability to use virtual memory (VM) with third-party software, although Apple didn’t include VM as part of the Mac OS until System 7 in 1991.

The 68030 can also be used with a newer, more powerful FPU (floating point unit, a.k.a. math coprocessor), the 68882. Overall performance of the 68030 is comparable to the 68020, although the newer chip was eventually available at higher speeds and made its way into the “wicked fast” 40 MHz Mac IIfx – and in a 50 MHz version on some accelerator cards.

The 68030 includes a new memory addressing mode that is one-third faster than on the 68020.

The 25 MHz Mac IIci (Sept. 1989) was the first Mac with a level-2 (L2) cache slot – and also the first faster than 16 MHz and the first with 32-bit “clean” ROMs.

Although the 68030 has two 256-byte caches (twice as much as the 68020), the speed differential between the 25 MHz data bus and 80ns system memory prevents the IIci from achieving its full potential. A relatively small 32 KB L2 cache would boost performance 20-30%. (Larger 64 KB and 128 KB caches were also available, but added so little with a 25 MHz CPU that they didn’t catch on. A 32 KB cache was enough – and Apple eventually made it standard on the IIci. Cache cards use a different kind of memory, static RAM or SRAM, with 25ns or faster performance.)

In addition to Macs, the 68030 was used in some Amiga, Atari ST, and NeXT computers.

Next: Motorola 68040

Summary, 680×0 family

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: #motorola68030 #motorolacpus

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