The Macintosh IIsi is a

personal computer A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or te ...

designed, manufactured and sold by Apple Computer, Inc. from October 1990 to March 1993. Introduced as a lower-cost alternative to the other

Macintosh II family The Macintosh II is a family of personal computers that was designed, manufactured and sold by Apple Computer, Inc. from 1987 to 1993. The Macintosh II was the initial model, representing the high-end of the Macintosh line for the time. Over th ...

of desktop models, it was popular for home use, as it offered more expandability and performance than the

Macintosh LC The Macintosh LC is a personal computer designed, manufactured, and sold by Apple Computer, Inc. from October 1990 to March 1992. Overview The first in the Macintosh LC family, the LC was introduced with the Macintosh Classic (a repackaging o ...

, which was introduced at the same time. Like the LC, it has built-in sound support, as well as support for color displays, with a maximum screen resolution of 640 × 480 in 8-bit color. The IIsi remained on the market for two and a half years and was discontinued shortly after the introduction of its replacement, the Centris 610.

Hardware

The IIsi's case design is a compact desktop unit not used for any other Macintosh model, one of the few Macintosh designs that was used for a single model. Positioned below the

Macintosh IIci The Macintosh IIci is a personal computer designed, manufactured, and sold by Apple Computer, Inc. from September 1989 to February 1993. It is a more powerful version of the Macintosh IIcx, released earlier that year, and shares the same comp ...

as Apple's entry-level professional model, the IIsi's price was lowered by the redesign of the motherboard substituting a different memory controller and the deletion of all but one of the expansion card slots (a single

Processor Direct Slot A processor direct slot (PDS) is a slot incorporated into many older Macintosh models that allowed direct access to the signal pins of a CPU, similar to the functionality of a local bus in PCs. This would result in much higher speeds than having ...

) and removal of the level 2 cache slot. It shipped with either a 40-MB or 80-MB internal hard disk, and a 1.44-MB floppy disk drive. The

Motorola 68882 The Motorola 68881 and Motorola 68882 are floating-point units (FPUs) used in some computer systems in conjunction with Motorola's 32-bit 68020 or 68030 microprocessors. These coprocessors are external chips, designed before floating point math bec ...

FPU was an optional upgrade, mounted on a special plug-in card. Ports included

SCSI Small Computer System Interface (SCSI, ) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical interface ...

, two serial ports, an ADB port, a floppy drive port, and 3.5mm stereo headphone sound output and microphone sound input sockets. A bridge card was available for the IIsi to convert the Processor Direct slot to a standard internal

NuBus NuBus (pron. 'New Bus') is a 32-bit parallel computer bus, originally developed at MIT and standardized in 1987 as a part of the NuMachine workstation project. The first complete implementation of the NuBus was done by Western Digital fo ...

card slot, compatible with other machines in the Macintosh II family. The bridge card included the 68882 FPU to improve floating-point performance. The NuBus card was mounted horizontally above the motherboard. To cut costs, the IIsi's video shared the main system memory, which also had the effect of slowing down video considerably, especially as the IIsi had 1 MB of slow RAM soldered to the motherboard.

David Pogue David Welch Pogue (born March 9, 1963) is an American technology and science writer and TV presenter. He is an Emmy-winning correspondent for ''CBS News Sunday Morning'' and author of the "Crowdwise" column in ''The New York Times'' Smarter Livi ...

's book ''Macworld Macintosh Secrets'' observed that one could speed up video considerably if one set the disk cache size large enough to force the computer to draw video RAM from faster RAM installed in the

SIMM A SIMM (single in-line memory module) is a type of memory module containing random-access memory used in computers from the early 1980s to the early 2000s. It differs from a dual in-line memory module (DIMM), the most predominant form of memo ...

banks. The IIsi also suffers from sound difficulties: over time, the speaker contacts can fail, causing the sound to periodically drop out. This problem was caused by the very modular construction of the computer, where the mono loudspeaker is on a daughterboard under the motherboard, with springy contacts. Speaker vibrations led to

fretting Fretting refers to wear and sometimes corrosion damage of loaded surfaces in contact while they encounter small oscillatory movements tangential to the surface. Fretting is caused by adhesion of contact surface asperities, which are subsequent ...

of the touching surfaces. The problem could be solved by removing the motherboard and using a pencil eraser to clean the contacts of the daughterboard holding the loudspeaker. As the IIsi is the only Macintosh to use this case design, these issues were never corrected in a subsequent model. The IIsi was designed to be easily and cheaply manufactured, such that no tools were required to put one together – everything is held in place with clips or latches. Because of its heritage as a cut-down IIci, it was a simple modification to substitute a new

clock A clock or a timepiece is a device used to measure and indicate time. The clock is one of the oldest human inventions, meeting the need to measure intervals of time shorter than the natural units such as the day, the lunar month and ...

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...

to increase the system's

clock rate In computing, the clock rate or clock speed typically refers to the frequency at which the clock generator of a processor can generate pulses, which are used to synchronize the operations of its components, and is used as an indicator of the pr ...

to 25 MHz for a slight increase in performance and a large increase in video rendering speed.

Known users

Charles Bukowski Henry Charles Bukowski ( ; born Heinrich Karl Bukowski, ; August 16, 1920 – March 9, 1994) was a German-American poet, novelist, and short story writer. His writing was influenced by the social, cultural, and economic ambience of his adopted ...

was an enthusiastic user of the IIsi.

Timeline

References

External links

Macintosh IIsi teardown
at ifixit.com {{Apple hardware before 1998 si IIsi IIsi IIsi IIsi Computer-related introductions in 1990