Macintosh IIsi

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.


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.

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).


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. 


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