The Macintosh IIfx was on the market from 1990 to 1992. It was the fasted macintosh available at the time. It ran on the Motorola 68030 which was clocked at 40MHz. The machine came with 4MByte RAM, expandable to 128MByte. In addition the IIfx had 32KByte of Level 2 cache, six NuBus slots, and a number of proprietary ASICs (Application Specific Integrated Circuit) and coprocessors.
This machine was designed for speed. the Asics needed system-specific drivers to run. Even the RAM was optimized. The system uses high-speed (80 nano-second) RAM using 64 pin dual-ported SIMMS. Other Macintosh models used 30-pin SIMMS. The extra pins allowed a separate path to allow latched read and write operations.