Apple introduced the Macintosh IIsi along with two other low cost Macs, the Macintosh Classic and Macintosh LC, on October 15, 1990. The Macintosh IIsi is a low cost version of the Macintosh IIci in a smaller case. The Macintosh IIsi has a unique case used by no other Macintosh model. It is a little over an inch taller and slightly shorter in length than the Macintosh LC. The Macintosh IIsi originally cost between $3770 and $4570 depending on options. I purchased my IIsi in 2008 for $40.
Apple intended the Macintosh IIsi to be the low cost home use alternative to its professional line of Macintosh II desktop computers. Cost saving measures included eliminating the NuBus expansion slots, soldering 1 MB of RAM on the motherboard, and using a slower processor. The Macintosh IIsi uses a 20 MHz 68030 processor with an optional 68882 FPU that can be installed using a special PDS NuBus bridge card described later. Apple intentionally included the slower 20 MHz processor in the IIsi to keep it from competing with the far more expandable IIci. The IIsi is however capable of running at the IIci's 25 MHz speed because it uses the same basic parts, which are rated at 25 MHz. Clock chipping the IIsi's 20 MHz processor to 25 MHz is possible.
Like the Macintosh LC, the IIsi has a single Processor Direct Slot (PDS) for expansion. Apple offered a $249 bridge card for the IIsi that converts the PDS to a standard NuBus card slot, compatible with the other II-series Macs. This bridge card includes a 68882 FPU to improve floating-point performance. NuBus cards are installed on this card perpendicular to the motherboard. The Macintosh IIsi has a horizontal port door that can be removed for cards that have a port. LC type PDS cards are not compitable with the IIsi.
Macintosh IIsi NuBus Adapter card with 68882 FPU
The Macintosh IIsi has the following ports: one ADB port, one DB-15 video port, one DB-19 floppy disk drive port, one DB-25 SCSI port, one serial printer port, one serial modem port, one microphone jack, and one speaker jack. The IIsi does not have an internal microphone. Apple shipped an external microphone with the IIsi. The microphone kit also includes a phono-plug adapter for stereo sound input, but the IIsi records in mono, mixing both channels into one sound.
Macintosh IIsi ports
Apple officially states that maximum RAM for the IIsi is 17 MB, but a maximum RAM of 65 MB is possible using a 4-SIMM bank of 16 MB 100ns 30-pin memory. Apple never officially supported 8 MB or 16 MB SIMMs. The IIsi has four RAM slots and 1 MB of RAM soldered to the motherboard. My IIsi has 17 MB of RAM (four 4 MB SIMMs with 1 MB on the motherboard).
Macintosh IIsi with top cover removed
The IIsi is capable of generating 256 colors (8-bit) at 513 x 384 or 640 x 480. My IIsi is using a very well preserved 13 inch (12.8 inch viewable) AppleColor High-Resolution RGB Monitor capable of a only a single resolution of 640 x 480. This monitor is very heavy. The IIsi's video shares the main system memory, which considerably slows down video graphics since the video function draws first from the 1 MB of slow RAM soldered to the motherboard. It is possible to speed up video graphics by setting the disk cache size large enough to force the computer to draw video from faster RAM installed in the SIMM banks. Disk cache size is set in the Memory Control Panel.
Set disk cache size in Memory Control Panel
The Macintosh IIsi originally shipped with Mac OS 6.0.7 and it supports up to Mac OS 7.6.1. My IIsi is using Mac OS 7.5. The Macintosh IIsi is a pre-System 7 Mac, but it is fully equipped to run System 7 and includes so-called clean 32-bit ROM chips. There is a ROM SIMM slot on the IIsi that can be filled with a rare IIsi ROM SIMM. All IIsi's have this ROM SIMM slot whether or not they actually shipped with it. Most IIsi computers have ROMs soldered on the motherboard. Those IIsi's that shipped with the ROM SIMM will not run without it. It may be possible to turn a Macintosh SE/30 into a clean 32-bit system by using a IIsi ROM SIMM. Thus, collectors are always on the look out for the presence of a IIsi ROM SIMM whenever a IIsi goes up for auction on eBay.
Macintosh IIsi ROM SIMM slot
"About This Macintosh" showing Mac OS and RAM
Click to view screen capture 1 - About
Click to view screen capture 2 - Calculator
Click to view screen capture 3 - Control Panels
Click to view screen capture 4 - Monitor Control Panel
Click to view screen capture 5 - Memory Control Panel
Click to view screen capture 6 - Power Central Control Panel
The IIsi shipped with either a 40 MB or 80 MB internal SCSI hard disk drive. My IIsi has an 80 MB internal hard disk drive. The IIsi has a single internal 1.4 MB floppy disk drive. I purchased my IIsi on eBay in an auction that clearly stated that this IIsi did not have an internal hard disk drive. This was great. Neophytes are easily scared off by such pronouncements even in light of the fact that this IIsi included a DayStar PowerCache 030 50 MHz accelerator card. Adding a hard drive takes about two seconds, so such things do not deter the informed buyer. The DayStar P33 accelerator is harder to find than a relatively common IIsi with a good internal hard drive. Couple that with the fact that this IIsi does not have the rare IIsi ROM SIMM and I was able to purchase this excellent IIsi system with AppleColor High-Resolution RGB Monitor, extended AppleDesign keyboard, and ADB Mouse II for almost nothing.
DayStar PowerCache 030 50 MHz (P33)
|DayStar PowerCache card and Apple NuBus Adapter card installed on DayStar riser card
DayStar PowerCache card installed in IIsi
The DayStar PowerCache 030 50 MHz (P33) is an accelerator card that more than doubles the speed of the 20 MHz IIsi. In my IIsi, this card is installed on a DayStar PDS riser card with two slots. The riser card allows the user to install both the PowerCache card and the Apple NuBus Adapter card with 68882 FPU. The only software required to run the PowerCache card is the DayStar Power Central Control Panel, which shipped along with the card on a 1.4 MB floppy disk. DayStar also included the PowerDemo application on the disk (see PowerDemo screen captures below). PowerDemo allows the user to test the card by running it through a series of speed tests.
DayStar Power Central Control Panel
Click to view PowerDemo DayStars test
Click to view PowerDemo Lines test
Click to view PowerDemo Disk I/0 test
Click to view PowerDemo Fractal test
The Macintosh IIsi is a unique Mac with no successors making it a must have in any Apple collection. The IIsi was a good overall computer to have at home in 1990, offering a balanced mix of price over performance. For those who like to hack, it can be modified to run faster, but for those who have better things to do, accelerator cards like the DayStar P33 are plentiful.