Draft:Multifunction card

The multifunction card and/or multi-I/O card was a commonly-installed ISA peripheral card in the early days of IBM-compatible PCs. This class of third-party peripheral cards emerged on the budding PC market in response to limitations of the original IBM PC and XT's design – limitations that initially were also copied by vendors of clone PCs: PC/XT-class machines only included very few ports onboard; mainly just the keyboard and cassette port (the latter was little-used and only present on the original PC, but not the XT and most clones). At the same time, the original PC only had five ISA slots, no onboard video or disk controllers, and upgrading the limited onboard memory to 640K required the addition of at least one ISA RAM card, stealing yet another slot or two. Running out of expansion slots for essential functionality was thus a real possibility. IBM recognised and responded to the problem by increasing the number of ISA slots to eight in the XT, but it was still possible to run out of those. To help prevent that, third-party vendors were quick to offer peripherals that combined many of the frequently-desired or required features on a single card.

These feature included:

• serial ports
• a parallel port
• a floppy disk controller
• a real-time clock, often with button cell battery backup
• RAM card functionality
• a game port
• possibly a hard disk controller; initially MFM/RLL, later IDE, rarely SCSI

At a minimum, a multi-I/O card offered two serial ports and one parallel port. Such limited multifunction cards were generally just called multi-I/O cards. Most multifunction cards commonly thusly named offered more, but not all multifunction cards offered everything. Technically IBM's Monochrome Display Adapter could also be called multi-function, since it included a printer port – however the MDA was not generally recognised as part of this class of cards, and multifunction cards generally did not include display adapter functionality. The addition of those three extra ISA slots in the XT lessened the need for multifunction cards, and from the AT generation onwards, greater IC integration and miniaturisation allowed for more ports and peripherals to be included on the motherboard, a process that got semi-standardised after the release of the ATX standard, at which time most of the above ports and features were onboard. The very advances which had allowed quick-reacting third-party vendors to include so many features on ever-shrinking peripheral cards—advances in the then-new field of VLSI, which superseded older and larger discrete TTL logic—ultimately also allowed OEM manufacturers to include many of the same features right on the motherboard. Also, later on, some of the above functionality was replaced by the arrival of USB, though the minor boom in multifunction cards was already over at that point. Generally, multifunction and multi-I/O cards as described here were ISA cards; by the time the PCI bus arrived, the pressing need for them had mostly disappeared. The multifunction cards described herein enjoyed their greatest popularity in the 1980s and at most early 1990s. The fashionable trend to prefer slimline cases (with riser cards and fewer available slots) which peaked around the turn of the decade (late 1980s/early 1990s) temporarily once again increased the demand for multifunction cards, giving them a second wind towards the end, but following that, the multifunction card as a generally-recognised identifiable class of PC peripherals largely disappeared.

Multifunction cards should not be confused with multi-function card units or machines; altogether different IBM technologies that preceded the IBM PC by decades. These units or machines were pieces of (physically very large) proto-computing hardware that could perform multiple punch card processing functions.