One of the early strengths of the Apple II line, and one of the most important factors contributing to its success, was its open architecture, epitomized by its generous number of internal expansion card slots, or simply expansion slots. These slots accommodated a host of Apple II peripheral cards (which many users simply called "cards"), which added to and extended the functionality of the base system. All Apple II models, with the exception of the portable, slot-less Apple IIc series, had at least seven 50-pin expansion slots, labeled Slots 1 though 7. These slots could hold printed circuit board cards with double-sided edge connectors, 25 "fingers" on each side, with 100-mil (0.1-inch) spacing between centers.
In addition to the seven standard expansion slots, the following computers contained additional, largely special-purpose expansion slots:
Apple II and Apple II Plus: 50-pin "Slot 0" (e. g., for the 16-kB Apple II Language Card)
Apple IIe: 60-pin "Auxiliary Slot" (primarily for 80-column display and memory expansion)
Apple IIGS: 40-pin "Memory Expansion Slot"
Perhaps the most common cards found on early Apple II systems were the Disk II Controller Card, which allowed users of earlier Apple II's to use the Apple Disk II, a 5¼-inch, 140-kB floppy disk drive; and the Apple 16K Language Card, which increased the base memory of late-model Apple IIs and standard Apple II Pluses from 48 kB to 64 kB. Both Apple Computer, Inc., and dozens of third-party vendors created hundreds of cards for the Apple II series of computers. These expansion slots afforded virtually limitless opportunities for expansion, far beyond what was available on other microcomputers of the time. Even today, long after the last Apple IIe came off Apple's assembly line in 1993, a handful of manufacturers continue to market peripherals and expansion cards for Apple II computers, not counting the hundreds of students, hobbyists, and other loyal Apple II users who continue to push the original machine to the limits.
Card Categories
Apple II cards can be broadly divided into the following categories:
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