Apple  Macintosh II-SI
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Macintosh IIsi

The Macintosh IIsi was released to the market in 1990. It was introduced as alower cost version of the other Macintosh II computers. Because of this lower cost, it was a popular model for home users. The machine was introduced at the same time as the Macintosh LC

The Macintosh IIsi ran on a Motorola 68030 @20MHz, came with 1MByte of RAM, built in sound and color video up to 640x480 in 8-bit color. It shipped with a 40MByte or 80MByte harddrive, and a 1.44MByte floppy disk drive.

The machine could be upgraded using the MC68882 Floating Point Unit (FPU), that was mounted on a special plug-in card. The machine also had SCSI, two serical port, an external floppy drive port, a sound input jack, and a 3.5mm stereo headphone jack.

Motorola 68000 CPU Family

The Motorola 68000 is a 16/32-bit microprocessor that was first released in 1979. It was widely used in computers and other electronic devices during the 1980s and early 1990s. The 68000 was known for its advanced architecture, which included a 32-bit internal bus and a 24-bit address bus, allowing it to access up to 16 megabytes of memory. This made it more powerful than many other processors of its time, such as the Intel 8086 and Zilog Z80. It was also designed to be highly modular and expandable, with a large number of on-chip and off-chip peripherals.

Some of the most famous and successful computers that used the 68000 was the Commodore Amiga and the Atari ST, both of which were popular in the home and personal computer markets. Additionally, it was also used in workstations, such as the Sun 3 and Apollo DN3000, and in a wide variety of embedded systems and industrial control systems. The 68000 was also used in the Macintosh, the first model of the Macintosh was powered by a Motorola 68000 CPU. The processor was eventually succeeded by the 68020 and 68030, which offered improved performance and additional features.

The 68000 has a 32-bit instruction set, with 32-bit registers and a 16-bit internal data bus. The address bus is 24-bit and does not use memory segmentation, making it easier to address memory. There are three ALU's (Arithmetic Logic Unit), two for calculating addresses, and one for data, and the chip has a 16-bit external address bus.

The 68000 architecture was expanded with 32-bit ALUs, and caches. Here is a list with some 680x0 versions and their major improvements:

  • 68010 - Virtual memory support
  • 68020 - 32-bit ALU & Instruction Cache
  • 68030 - On-Chip MMU, 2x 256 byte cache
  • 68040 - 2x 4K Cache, 6 stage pipeline, FPU
  • 68LC040 - No Floating Point Unit (FPU)
  • 68060 - 2x 8K Cache, 10 stage pipelinet

Technical Details
Released 1990 Brand Apple Type Apple Macintosh II Name Macintosh II-SI CPU Class 68000 CPU Motorola 68030 @20MHz Memory RAM: 1MB
RAM max: 17MB
Sound Chip TTL Logic for PWM Sound 8-bit Pulse-width modulation Display Chip none Display 640x480 4-bit color
512x384 8-bit color.
Best Color 8 bit color Best Graphics 640x480 4 bit color Sprites none System OS MacOS System 6 or 7
Related Systems
Apple Series I
Apple Series II
Apple Series III
Apple Macintosh
Apple Macintosh II
Macintosh  II-SI (1990)
Apple Macintosh LC & Quadra
Apple Newton
Related Media
Apple Macintosh
Books about the Apple Macintosh, the first mass-market personal computer with a graphical user interface.
68' Micro Journal
Magazine devoted to the 68xx user
InCider and A+
InCider Magazine for Apple Computers, later fused with A+
Peeker Magazine
Peeker, a German language magazine for Apple Computer users.
World Wide Web Links
Wikipedia: Motorola 68000 CPU Family
WikiPedia page on the Motorola 68000 series of processors