The motherboard has been
an integral part of most
personal computers for more than 20 years. Think of a motherboard as a
scale model of a futuristic city with many modular plug-in buildings, each
using power from a common electrical system. Multiple-lane highways of
various widths transport data between the buildings. The motherboard is the
data and power infrastructure for the entire computer.
Motherboards (also called mainboards) are actually a carryover
from architecture used for years in
computers. Various circuit cards performing various functions all plug
into many similar sockets on a common circuit board. Each circuit card
performs a unique function in the computer and gets its power from the
Due to improvements in circuitry and packaging, motherboards have
essentially stayed the same size or shrunk while their functionality has
skyrocketed. In this edition of
HowStuffWorks, you will learn how the motherboard operates and what
its many sockets and connectors do.
They made it easy to add new features to the machine over time.
They opened the computer to creative opportunities for third-party
The original IBM PC contained the original PC motherboard. In this design,
which premiered in 1982, the motherboard itself was a large printed circuit
card that contained the 8088
BIOS, sockets for the CPU's
RAM and a collection
of slots that auxiliary cards could plug into. If you wanted to add a
disk drive or a
or a joystick,
you bought a separate card and plugged it into one of the slots. This
approach was pioneered in the mass market by the Apple II machine. By making
it easy to add cards, Apple and IBM accomplished two huge things:
Different motherboards of different vintages typically have different
form factors. The form factor is essentially the size, shape and design
of the actual motherboard. There are more than a half-dozen form factors for
motherboards -- check out PC Guide's
Motherboard Form Factors to find out about the various designations.
The motherboard, by enabling pluggable components, allows users to
personalize a computer system depending on their applications and needs.
On the Motherboard
A motherboard is a multi-layered printed circuit board. Copper
circuit paths called traces that resemble a complicated roadmap carry
signals and voltages across the motherboard. Layered fabrication techniques
are used so that some layers of a board can carry data for the
buses while other layers carry voltage and ground returns without the paths
short-circuiting at intersections. The insulated layers are manufactured
into one complete, complex sandwich. Chips and sockets are soldered onto the
The MSI 694D Pro AR supports dual Pentium microprocessors, has five
PCI slots and a
communications network riser (CNR) slot. The board supports 133 MHz bus
speeds and ultra-direct memory access-100 (UDMA). There are four
USB ports and
onboard audio in the ATX form factor board.
MSI 694D Pro AR Dual Flip Chip Socket 370 motherboard
The Abit KT-7A supports Advanced Micro Devices (AMD) processors and has
the KT-133A chipset. The card slots on the Abit KT-7A, from bottom to top in
the image below, shows that ISA has one slot, PCI has six slots and
AGP has one slot. A
special fan cools the chipset.
Abit KT-7A AMD Processor Motherboard
A partial view of the TechRam S3ProM motherboard shows slots: From bottom
to top, ISA has one slot, PCI has two slots, audio modem riser (AMR) has one
slot, and AGP has one slot.
TechRam S3ProM Motherboard
The BIOS chip is common to many motherboards.
Data Bus Width
Modern Pentium class motherboards have a data bus with 64
bits. That is the
width of the data highway that goes in and out of the processor. The Pentium
processors, however, do use 32-bit registers to handle 32-bit instructions.
Bus speeds and widths have increased due to faster processors and the
needs of multimedia applications. Typical bus names and widths are:
- Industry Standard Architecture (ISA) - 8 or 16 bits
- Extended Industry Standard Architecture (EISA) - 8 or16 bits
- Microchannel Architecture (MCA) - 16 or 32 bits
- VESA Local Bus (VLB) - 32 bits
- Peripheral Component Interconnect (PCI) - 32 or 64 bits
- Accelerated Graphics Port (AGP ) - 32 bits
Chipsets provide the support for the processor chip on the
motherboard. The Intel 440BX is the dominant chipset in the non-Apple
The chipset is the heart of the computer since it controls and determines
how fast and which type of processor, memory, and slots are used. Another
chip on the motherboard is called the Super I/O controller. Its main
function is to control the
printer ports. Check out PCGuide's
Super I/O Controller Functions to learn more.
Recent motherboard designs include additional chips to support USB, sound
card, video adapter, computer host and
adapter. These chips save the cost of an adapter slot.
temperatures, density, faster chipset designs and component count have
driven the need for circuit cooling via miniature electric fans. These fans
mount inside the actual computer case. Heat sinks act like a
providing additional surface area to help cool a component.
Replaceable fan/heat-sink assemblies are often used to help dissipate the
considerable amount of heat on modern processor chips. The assembly conducts
heat away from the chip by convection, using a layer of thermal grease
between the two mating metal surfaces. Fans often have a third wire used for
monitoring the speed of the fan.