More confusing than board designs is the terminology used to describe the motherboard. The industry is rife with words that mean the same thing as "motherboard" or have subtle variations from that definition. Here are some of the most common:
This term is little more than a desexed version of motherboard, introduced to the realm of personal computer by IBM when it introduced its first machine. At the time America was preoccupied with issues of sexual equality, and well-meaning but linguistically naive people confused issues of gender with sex. The term system board stands in its own right, however, because it indicates the role of the board as the centerpiece of the entire computer system. IBM continues to use the term to mean motherboard.
Although planar board may seem simply another desexed word for motherboard, it bears a distinction. Although all modern circuit boards are planar in the sense they take the form of a flat plane, the planar board in a computer forms the mounting plane of the entire system.
Intel often refers to the motherboard as the baseboard in many of its technical manuals. The company is not consistent about its usage—for example, the manual dated May, 1996, for Intel VS440FX lists the product as a "motherboard," whereas the manual for the Performance/AU, dated December 1995, terms the product a "baseboard." Again, there is a subtle distinction. A motherboard goes into a computer; a baseboard decorates the junction of a wall and the floor.
Apparently contributed by offshore motherboard-makers, the term main board may be a result of translation, but it is actually a particularly appropriate term. The "main board" is the largest circuit board inside and the foundation for the computer system and, hence, it is the main board in a computer's case.
In the realm of the Apple Macintosh, the term logic board often refers to the equivalent of a computer's motherboard—notwithstanding, every printed circuit board inside a computer contains digital logic.
Another term sometimes used to describe the motherboard in computers is backplane. The name is a carryover from bus-oriented computers. In early bus-oriented design, all the expansion connectors in the machine were linked by a single circuit board. The expansion boards slid through the front panel of the computer and plugged into the expansion connectors in the motherboard at the rear. Because the board was necessarily planar and at the rear of the computer, the term backplane was perfectly descriptive. With later designs, the backplane found itself lining the bottom of the computer case.
Backplanes are described as active if, as in the computer design, they hold active logic circuitry. A passive backplane is nothing more than expansion connectors linked by wires or printed circuitry. The system boards of most personal computers could be described as active backplanes, although most engineers reserve the term backplane for bus-oriented computers in which the microprocessor plugs into the backplane rather than residing on it. The active circuitry on an active backplane under such a limited definition would comprise bus control logic that facilitates the communication between boards.