Mac IIfx

Six months after moving from 16 MHz to 25 MHz with the IIci, Apple introduced the “wicked fast” 40 MHz IIfx. This was the Mac of choice for graphic designers, offering nearly three times the performance of the IIx – thanks to a lightning fast CPU, a new type of RAM, and special SCSI DMA and I/O chips which relieved the CPU of much of its burden. A built-in 32 KB static RAM cache also helps boost performance.

Macintosh IIfx with RGB displayThe IIfx was built on a 40 MHz motherboard and had the fastest clocked CPU that Apple used until the Quadra 840av of 1993. NuBus cards still ran on a 10 MHz bus, which is one reason Apple announced its first accelerated video card, the 8•24GC, along with the IIfx. Regular video cards were simply overshadowed by the rest of the system.

With a nod to it’s Apple II ancestors, the IIfx had two 6502 CPUs to manage the floppy drive(s), ADB port, and serial ports (see Technote HW 09 for more details). Unlike the 1 MHz Apple II computers, these CPUs ran at 10 MHz.

The IIfx introduced latched read/write RAM to the Apple lexicon. Using a 64-pin SIMM different from that in any other Macintosh, the IIfx could overlap read and write operations. (Byte, 4/90, p. 112)

The IIfx requires a special “black” SCSI terminator to accommodate its unusual architecture (see Termination Explained for more details).

There is a ROM SIMM slot on the Mac IIfx that must be filled with a IIfx ROM. Without this ROM, the computer will not function.

Although appearing identical to the Mac II and IIx, the IIfx power supply has a variable speed fan to better control noise and cooling.

Dash 30fx, a IIfx on Steroids

A company known as 68000 repackaged the Mac IIfx logic board in a huge, heavy metal case, overclocked the board to 50 or 55 MHz, replaced the 40 MHz CPU and FPU with the 50 MHz version, installed even faster RAM, and turned the “wicked fast” IIfx into something 25-35% faster!

Upgrade Advice

Accelerators are almost unknown for the IIfx, so many years after it was discontinued.

  • IIfx RAM is relatively costly, but you should have at least 8 MB. When upgrading, consider putting as much in one bank as possible, leaving the other bank for future expansion.
  • An accelerated video card can make a world of difference, particularly if you use 16-bit or 24-bit modes or a monitor larger than 640 x 480 pixels. See our NuBus Video Card Guide for lots of information.
  • A newer hard drive will be larger and faster than the one Apple shipped with the computer, but you won’t be able to take full advantage of that speed on the IIfx without a SCSI accelerator.
  • More RAM plus Speed Doubler equals improved hard drive performance through intelligent caching.

Because it uses oddball memory and has some unusual circuitry, we label the IIfx a Limited Mac.


  • introduced 1990.03.19 at $9,900; discontinued 1992.04.15
  • code names: F-16, F-19, Stealth, Blackbird, Zone 5, Four Square, IIxi, Weed Whacker
  • model no.: M5525
  • Gestalt ID: 13

Mac OS

  • requires System 6.0.5 to 7.6.1
  • addressing: 24-bit or 32-bit

Core System

  • CPU: 40 MHz 68030
  • FPU: 40 MHz 68882 FPU
  • Bus: 40 MHz – fastest until Quadra 840av
  • ROM: 512 KB
  • RAM: 4 MB, expandable to 128 MB using both 4-SIMM banks of 80ns 64-pin memory; can use 1 MB, 4 MB, 8 MB, and 16 MB SIMMs (the IIfx was the only Mac to use 64-pin SIMMs)
  • L2 cache: 32 KB


  • 6.8, relative to SE
  • 4.60, MacBench 2.0 CPU
  • 11.45, Speedometer 3.06
  • 0.71, Speedometer 4
  • 10.0 MIPS
  • see Benchmarks: IIfx for more details



  • Hard drive: 40, 80, or 160 MB SCSI
  • floppy drive: 1.4 MB double-sided
  • internal bay for second floppy drive


  • ADB ports: 2
  • serial ports: 2 DIN-8 RS-422 ports on back of computer
  • SCSI ports: DB-25 connector on back of computer
  • sound: 8-bit stereo
  • NuBus slots: 6
  • one PDS slot (inline with a NuBus slot)


  • size (HxWxD): 5.5″ x 18.7″ x 14.5″
  • Weight: 24 lb.
  • PRAM battery: 3.6V half-AA
  • power supply: 230W


Discontinued accelerators (all are 68040) include the Applied Engineering TransWarp (25, 33 MHz 68040), Fusion Data TokaMac FX (33 MHz 68040), and Radius Rocket (25 MHz 68LC040 to 40 MHz 68040).

Online Resources


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