"Wicked fast" entered the Macintosh vocabulary when Apple rolled out the 40MHz IIfx in March 1990. This was the Mac of choice for graphic designers, offering nearly three times the performance of the IIx, thanks to a lightning fast CPU, an improved memory architecture, and special DMA chips which relieved the CPU of much of its I/O burden. A built-in 32KB static RAM cache also helps boost performance.
The IIfx requires a special "black" SCSI terminator to accommodate its unusual architecture.