Editing Micro Channel architecture (section)

===Overview===
The Micro Channel was primarily a 32-bit bus, but the system also supported a 16-bit mode designed to lower the cost of connectors and logic in [[Intel]]-based machines like the IBM [[PS/2]].

The situation was never that simple, however, as both the 32-bit and 16-bit versions initially had a number of additional optional connectors for memory cards which resulted in a huge number of physically incompatible cards for bus attached memory. In time, memory moved to the CPU's [[local bus]], thereby eliminating the problem. On the upside, signal quality was greatly improved as Micro Channel added ground and power pins and arranged the pins to minimize interference; a ground or a supply was thereby located within 3 pins of every signal.

Another connector extension was included for [[graphics card]]s. This extension was used for analog output from the video card, which was then routed through the system board to the system's own monitor output. The advantage of this was that Micro Channel system boards could have a basic [[VGA]] or [[Multi-Color Graphics Array|MCGA]] graphics system on board, and higher-level graphics ([[XGA]] or other accelerator cards) could then share the same port. The add-on cards were then able to be free of '[[legacy system|legacy]]' VGA modes, making use of the on-board graphics system when needed, and allowing a single system board connector for graphics that could be upgraded.

Micro Channel cards also featured a unique, 16-bit software-readable ID, which formed the basis of an early plug and play system.    The BIOS and/or OS can read IDs, compare against a list of known cards, and perform automatic system configuration to suit. This led to boot failures whereby an older [[BIOS]] would not recognize a newer card, causing an error at startup. In turn, this required IBM to release updated Reference Disks (The [[Nonvolatile BIOS memory|CMOS]] Setup Utility) on a regular basis. A fairly complete list of known IDs is available (see External links section). To accompany these reference disks were ADF files which were read by setup which in turn provided configuration information for the card. The ADF was a simple text file, containing information about the card's memory addressing and interrupts.

Although MCA cards cost nearly double the price of comparable non-MCA cards, the marketing stressed that it was simple for any user to upgrade or add more cards to their PC, thus saving the considerable expense of a technician. In this critical area, Micro Channel architecture's biggest advantage was also its greatest disadvantage, and one of the major reasons for its demise. To add a new card (video, printer, memory, network, modem, etc.) the user simply plugged in the MCA card and inserted a customized [[floppy disk]] (that came with the PC) to blend the new card into the original hardware automatically, rather than bringing in an expensively trained technician who could manually make all the needed changes. All choices for interrupts (an often perplexing problem) and other changes were accomplished automatically by the PC reading the old configuration from the floppy disk, which made necessary changes in software, then wrote the new configuration to the floppy disk. In practice, however, this meant that the user must keep that ''same floppy disk matched to that PC''. For a small company with a few PCs, this was annoying, but practical. But for large organizations with hundreds or even thousands of PCs, permanently matching each PC with its own floppy disk was logistically unlikely or impossible. Without the original, updated floppy disk, no changes could be made to the PC's cards. After this experience repeated itself thousands of times, business leaders realized their dream scenario for upgrade simplicity did not work in the corporate world, and they sought a better process.