Mac IIsi, a Compromised Mac

It’s debatable whether the Mac IIsi is really a Second Class Mac. The IIsi was a bit of an odd duck. On the one hand, it was the only Mac II to ship without a NuBus slot. On the other hand, it could be seen as a monitor-less SE/30.

Macinsoth IIsiThe great compromise was taking a good hardware design and running it at 20 MHz despite the fact that each and every component was capable of running at 25 MHz. (Apple didn’t want to cut into sales of the IIci.)

Like the SE/30, the IIsi has a 68030 processor direct slot (PDS). Unlike the SE/30, it runs at 20 MHz, twice the speed of a NuBus slot and 25% faster than the 16 MHz SE/30. Unlike the SE/30, it is possible to put a NuBus adapter in this slot.

Like the IIci, the IIsi uses the first bank of RAM for video. Unlike the IIci, that 1 MB bank of RAM is soldered to the motherboard. This allowed Apple to cut costs by installing only one bank of SIMM sockets for memory expansion. It also limits expansion to 65 MB, which was pretty good by the standards of the day.

The IIsi was a very competent computer with few compromises. If it had used VRAM like the LC, it would have been a bit faster. If it had run at 25 MHz, that would have been nice. (BTW, the IIsi is frequently chipped to 25-28 MHz, which allows it to reach its full potential.)

With a 68040 PDS accelerator, the IIsi holds its own against a Quadra. However, the IIsi power supply, perfectly adequate for normal use, may be inadequate if you install a different hard drive, a video card, or a PDS card (such as an accelerator). The NuBus slot in the IIsi is rated at just 13.3W, less than many high resolution or 24-bit video cards require. The PDS is rated at just 7W. The normal hard drive draws 6W; if you replace it with a higher-draw drive, power to the NuBus slot or PDS is reduced accordingly.

The Mac IIsi was not a bad little computer at all, just one held back to avoid stealing Mac IIci sales.


  • introduced October 1990 at $3,800; discontinued March 1993
  • requires System 6.0.6 to 7.6.1
  • CPU: 20 MHz 68030
  • FPU: 68882 (optional with NuBus adapter)
  • performance: 2.9 (relative to SE)
  • 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 16 MB SIMMs, although Apple does not officially support them)
  • 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)
  • L2 cache: none
  • ADB: 2 ports for keyboard and mouse
  • serial: 2 DIN-8 RS-422 ports on back of computer
  • SCSI: DB-25 connector on back of computer
  • SE/30 PDS slot – can be converted to NuBus with adapter

Keywords: #maciisi #macintoshiisi

Short link:

searchword: iisiroadapple