The Once and Future Mac286 Page

This page is dedicated to the first MS-DOS coprocessor cards for the Macintosh, the Mac286 and its sibling the Mac86. I have created this page in response to the lack of information about these cards that is publicly available.

In 1987, Apple Computer released the first expandable Macintosh computers: the Macintosh SE and the Macintosh II. In those days, the gap between the worlds of the Mac and the IBM PC was much wider than it is today. To help bridge the gap, AST Research introduced a pair of MS-DOS coprocessor cards for the Mac. The Mac86 was an i8086-based card for the Mac SE, while the Mac286 was a higher performance i80286-based card for the Mac II.

In 1989, AST completed its exit from the Apple market and sold the rights and technologies for the cards to Orange Micro, a longtime player in the Apple marketplace. Orange Micro would go on to make a successful line of coprocessor cards based on the 80×86 processor family. By this writing (August 2001), Orange Micro had exited the coprocessor market to concentrate on USB and FireWire products.

In 1992, Orange Micro discontinued the Mac286 board. Support for the card was discontinued sometime later. [Editor's note: Orange Micro went out of business in 2004. dk]

This page is divided into several sections:

The Mac286 Hardware

There are three distinct versions of the Mac286 hardware:

  • The original AST version consists of a pair of full-length NuBus cards, joined by two ribbon cables. The first board consists of a CPU card while the second board acts as a disk controller and memory card.
  • The early Orange Micro version is similar to the AST version. It was reworked in some areas and contains additional circuitry, permitting memory upgrades.
  • The later Orange Micro version consists of a single board with a greater degree of VLSI chips.

Of the three versions, the AST appears to be the most common. Without knowing any sales figures, I cannot surmise whether this is due to there being a greater number of them or to the more expandable Orange Micro cards being more sought after.

Details of the hardware are as follows:

  • Intel 80286 processor, operating at 8 MHz or 12 MHz, depending on version. (A 10 MHz version may also exist.)
  • Socket for an optional Intel 80287 math coprocessor
  • Phoenix 286 BIOS v3.00 (This is an AT BIOS.)
  • 1 MB non-parity RAM, organized as fouor 256K SIMMs (640K visible to MS-DOS)
  • NEC 765-based floppy controller (NOTE: Unlike most PC floppy controller boards, the circuit in the Mac286 allows for single density operation. This is primarily of interest to those wishing to read older CP/M diskettes with the appropriate software.)
  • 37-pin port for optional external floppy (Apple 5.25″ PC Drive or equivalent)

The Mac286 software provides emulation of the following additional hardware:

  • CGA or Hercules monochrome graphics card (switchable)
  • 1.44 MB floppy drive as drive A: (if a SuperDrive is installed in the Macintosh)
  • 20 MB hard disk, stored as a file on the host Mac.
  • Access to the file system of the Mac via an emulated drive D:
  • 0, 1, or 2 COM ports (These are mapped to the Mac’s Modem and Printer ports.)
  • Printer port, emulating either an Epson MX80 or an Apple LaserWriter. (The latter is only available if a real LaserWriter is connected to the system.)

If this all seems primitive, remember that this was 1989. Heatseekers could choose between systems running an Intel 80386-16 (20 MHz versions were still in short supply) or an AMD or Harris 80286-20. The typical office was a mixture of standalone PCs, PC/XTs, and PC/ATs. The dominant office applications were Lotus 1-2-3, WordPerfect 4.2, Ashton Tate’s dBase III, and Software Publishing’s Harvard Graphics 2.3. (Microsoft Access was a communication program that most people were trying to forget.) The dominant OS was MS-DOS, including IBM’s PC-DOS. Microsoft Windows 3.0 was still two years away, and relatively few native applications ran under Windows/286 and Windows/386 (as Win 2.X was known). It was the last dance for DOS, and the Mac286 was a respectable, if not cheap, date.


Finding a Mac286 board in 1998 is a largely “hit and miss” affair, requiring considerable determination and patience. Based on my own experiences, the three most likely places to find one are:

  1. NetNews classified ads
  2. Online auctions (eBay, in particular)
  3. Dealers in surplus Macintosh hardware

Figure on spending between $25-$30. For that price, you will likely get an AST Mac286 with a copy of the software (likely downloaded from here).


As is the case with most things in the PC world, the reasonable upgrade path for a Mac286 board is to replace it with a later Orange Micro card (386 or better). For those inveterate tinkerers/experimenters who want to see what can be done with the card, I present the following areas for consideration.

NOTE: The following are only suggestions based on upgrade strategies for a real PC. They may not be compatible with the Mac286 board and could potentially damage the board, your Mac, or both. As such, these suggestions are made without warranty and the author herewith disclaims any responsibility for damages that may occur.


Math Coprocessor

Back in the days when an IBM PC/AT was a workhorse system, one of the best upgrades you could install was an 80287 math coprocessor. If your common application mix made use of floating point arithmetic, it was common to see speed improvements of several hundred percent.

On the Mac286, the 80287 chip is installed in the empty 40-pin socket next to the CPU chip. It must be rated for at least 6 MHz operation.


The 80286 processor on the Mac286 is fitted in a PLC socket on the CPU card. In theory, it should be possible to replace the chip with an 80386SX or 80486SLC-based upgrade (such as the Make-It 486 product from Improve Technologies). This should give some increased performance.

The orientation of the processor and the spacing of the cards and the NuBus slots may, however, make it difficult to install. Also, I do not know what, if any, timing problems may be introduced by the new CPU chip.

Unfortunately, the 286 upgrade chips have been discontinued for sometime and are only available on the surplus market. If someone wants to give/loan me one, however, I would be willing to try it and report back on the results.


The Mac286 board comes equipped with 1 MB of non-parity memory. This comes in the form of four 256Kx8 30-pin SIMMs. Of this 1 MB, 640K is visible to MS-DOS. In theory, it should be possible to replace the 256K SIMMs with 1 MB SIMMs for a total of 4 MB.

In practice, the ability to upgrade the memory depends on which version of the card you have.

All Orange Micro versions of the Mac286 were designed to support a 4 MB RAM upgrade. Installing four 1 MB SIMMs will result in a system with 640K Real and 3008K Extended (3 MB minus 64K) memory.

The AST version, unfortunately, is limited to 1 MB of RAM. If you install four 1 MB SIMMs on an AST card, the power-on self test (POST) will only report 640K of memory and stop with a “Configuration Error- Run SETUP” message.

Background: The CMOS memory image for the emulated system is stored in a resource called “CMOS” in the Mac286 executable. There are two images, one for a 1 MB system and one for a 4 MB system. It appears that the Mac286 executable saw the fact that 4 MB of memory was installed and loaded the proper CMOS image. For some reason, however, the POST could not find the memory and stopped at 640K. Presumably, this is because of some address decoding hardware that is missing on the AST card.


The virtual C: drive of the Mac286 comes preinstalled with MS-DOS version 3.3. I have, however, successfully run newer versions of DOS including:

In all three cases, however, I was forced to sacrifice access to the Mac file system via the emulated D: drive. This was due to the inability of part of the disk redirector (dstep1.exe) to recognize and function with the alternative operating system. Using the SETVER command did not resolve the problem.

It may also be possible to install a small Unix-like operating system such as Minix or ELKS onto the virtual hard drive. I have not, however, attempted this yet, so I can not speak for the results.


Version 3.02 of the Mac286 software (the final version) is available from the Mac Driver Museum (MacBinaryII, 460K).

Version 2.1 of the Mac286 software (which seems to work better on some older Mac II’s) is also available from the Mac Driver Museum (MacBinaryII, 476K).

NOTE: You will need to turn off 32-bit addressing to run this software.


“The Mac286 Team”

Articles from Apple’s Knowledge Base Archive

Other Links

  • This is the only Mac286 page on the Web.
  • Low End Mac, lots of useful information on older Macs.
  • Mac Addict magazine’s This Old Mac, a good series of articles on making the most of “obsolete” Macs.
  • Mac286, Wikipedia

The original version of this page was posted to John Ruschmeyer’s Mac homepage account in 1998. The originals have long since vanished. This page is adapted from John’s original and posted here with his permission – links have been tested and sometimes replaced or deleted, and we’ve done a little editing. dk