Macintosh IIsi

Macintosh II si is the name of a computer manufactured by Apple.

The clocked at 20 MHz and based on the Motorola 68030 computer with a memory of 65 MB at maximum expansion was introduced by Apple in October 1990. To expand stood a PDS slot available, which could be converted via an adapter to a NuBus port. In addition to the 8 -bit color graphics card on the motherboard of the IIsi offered as all machines in the II series is an 8 -bit stereo sound system. On the external SCSI bus output disks, CD -ROM drives, scanners or streamer could be connected.

The Mac IIsi was a scaled-down version of the Macintosh IIci - as a cost-effective alternative for home users. To keep costs low, the graphics memory bandwidth divided as in the IIci with the CPU. In particular, higher resolutions and color depths were slower than the IIci. The on- board graphics could be operated in monochrome with a maximum resolution of 640 × 480 pixels with 8 bits or 640 x 870. Apple there were different monitors for the 15-pin video output of the device: a color monitor with a resolution of 512 x 384 pixels and two monochrome monitors with 640 x 480 or 640 x 870 pixels. A genuine Yamaha NuBus or LC PDS slot were on expansion board along with the 68882 coprocessor. 1 MB RAM were firmly soldered to the motherboard. The CPU of the IIsi was clocked at 20 instead of the IIci with 25 MHz, although the parts used were designed for 25 MHz processor clock. Therefore, the overclocking was (often up to 25 or 28 MHz) of the IIsi widespread, partly because of concurrency of CPU and graphics to the memory then worked much better and the graphics output was noticeably faster.

The newly designed motherboard of the Mac IIsi had a PDS expansion slot, for the special cards with the math coprocessor Motorola 68882 or bridge card were offered and could be plugged into the Processor Direct Slot, and an internal standard NuBus slot held that with was the other Macs IIsi series compatible. Offered was the IIsi with either 40 - or 80 -MB hard drive and a 1.44 MB floppy disk drive.

With the exception of the IIci IIsi one of the first Macs had with an audio input, which sometimes caused problems when wore down the speaker contacts over a longer period, which led to a failure of the sound output. This could only be corrected by cleaning the contacts and their treatment with silver paint. The first available ROMs were often flawed, which made the system from booting even impossible. Although Apple soon added a special ROM SIMM on subsequent boards for error compensation, the slot for the ROM SIMM remained preserved.