Mac IIsi

The IIsi shares some features with the SE/30, some with the LC series, and some with the Mac II series. Like the SE/30, it has a 68030 PDS (Processor Direct Slot) for expansion. Like the LC, it has no built-in NuBus slot, is quite short, and has a curved front. But with an adapter, the PDS can be converted to a NuBus slot, making it a legitimate member of the Mac II family (all other members of the Mac II family have built-in NuBus slots).

Macinsoth IIsiThe IIsi was designed as a less expensive, less expandable alternative to the Mac IIci. Cost saving measures included eliminating NuBus expansion slots, soldering 1 MB of RAM to the motherboard, and using a slower CPU (20 MHz instead of  25 MHz).

Although the IIsi was marketed as a 20 MHz computer, users quickly discovered it used parts rated at 25 MHz. (Apple had intended it as a 25 MHz computer, but chose to scale back the speed to avoid cutting into IIci sales.) Chipping the IIsi to 25 MHz – or even 28 MHz – is not unusual.

Like the IIci, the IIsi uses onboard RAM for video, which slows the computer slighty. One way to speed things up is to add either a PDS or NuBus video card (see our NuBus Video Card Guide for more information). Another is to set aside the first 1 MB of RAM, since that is the bank shared for video and program space. This can be done by creating a large-but-slow 768 KB disk cache or using IIsi-RAM-Muncher by Paul Ripke. (Note that this program is worthless if you’re using virtual memory or RAM Doubler.)

Along with the LC, the IIsi was one of the first Macs with audio input. The IIsi is noted for a sound problem where the internal speaker may fail to sound. This is usually caused by poor contact between the speaker wire and the plug on the motherboard and can often be fixed by cleaning and coating the contacts on the motherboard with electrical cleaner and lubricant.

There is a ROM SIMM slot on the Mac IIsi which may be filled with a IIsi ROM, although this is rare, since the IIsi generally has ROMs on the motherboard. If you have a IIsi with this ROM, the computer will not function without it. There are mixed reports from the field concerning compatibility of the IIsi ROM with the SE/30; installing a IIsi ROM should make an SE/30 32-bit clean.

Although a nice computer, the IIsi was a bit less than it should have been, so we call it a Compromised Mac.


  • introduced 1990.10.15 at $3,800; discontinued 1993.03.15
  • code names: Erickson, Raffica, Raffika, Ray Ban, Spin, Oceanic
  • Order no.: M0360
  • Gestalt ID: 10

Mac OS

  • requires System 6.0.6 to 7.6.1
  • addressing: 24-bit or 32-bit

Core System

  • CPU: 20 MHz 68030
  • FPU: 68882 (optional with NuBus adapter)
  • ROM: 512 KB, usually soldered to the motherboard, occasionally on a DIMM
  • RAM: 1 MB on motherboard, expandable to 65 MB using a 4-SIMM bank of 100ns 30-pin memory; can use 256 KB, 512 KB, 1 MB, 2 MB, and 4 MB SIMMs (you can use 8 MB and 16 MB SIMMs, although Apple does not officially support them)
  • L2 cache: none



  • built-in 8-bit video, supports 512 x 384 and 640 x 480 at 8-bits or portrait monitor (640 x 870) at 4-bits (uses 64-320 KB of RAM for video, not separate VRAM)
  • video port: DA-15


  • Hard drive: 40 or 80 MB SCSI
  • floppy drive: 1.4 MB double-sided
  • floppy connector on back of computer


  • 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
  • audio in: 8-bit mono
  • SE/30 PDS slot (runs at 20 MHz, so not all SE/30 cards will work – can be converted to NuBus slot with adapter)
  • NuBus slot with adapter in PDS, supports 7″ cards, 12″ cards may fit with a slim hard drive


  • size (HxWxD): 4.0″ x 12.4″ x 14.9″
  • Weight: 10 lbs.
  • PRAM battery: 3.6V half-AA
  • power supply: 160W

Online Resources

Discontinued accelerators (68030 unless otherwise noted) include the Applied Engineering TransWarp (25, 33 MHz 68040), DayStar Universal PowerCache (33, 40, 50 MHz), Fusion Data TokaMac SX (25 MHz 68040), Logica LogiCache (50 MHz), TechWorks NuBus (33 MHz 68040), and Total Systems Magellan (25 MHz 68040).

Accelerator Reviews

Online Resources


  • Never connect an Apple II 5.25″ floppy drive to the Mac’s floppy port. Doing so can ruin the floppy controller, meaning you can’t even use the internal drive any longer.
  • Internal video on the IIci and IIsi, and the Mac II mono and color video cards, will not work with multisync monitors, whether Apple or PC style. Griffin Technology made the Mac 2 Series Adapter, which works with Apple’s Multiple Scan monitors and most Mac compatible monitors. There was also a version for using VGA-type monitors on older Macs.
  • Serial port normally restricted to 57.6 kbps; throughput with a 56k modem may be limited. See 56k modem page. For more information on Mac serial ports, read Macintosh Serial Throughput in our Online Tech Journal.
  • The IIsi has an adequate power supply for normal use, but it could be inadequate if you install a different hard drive, a video card, or a PDS card. Although Apple specifies the NuBus slot at 15W, several high resolution or 24-bit cards require more. Worse, the NuBus slot in the IIsi is rated at just 13.3W. The PDS slot is rated at just 7W. The normal hard drive draws 6W; if you replace it with a higher-draw drive, power to the NuBus or PDS slot is reduced accordingly.
  • Internal video may reduce system and serial performance; a NuBus video card is recommended.

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