Motherboard
by John Anthony
The motherboard is the main circuit board in a PC. It
contains all the circuits and components that run the PC.
Major Components found on the motherboard are:
- CPU - the Central Processing Unit is often an
Intel Pentium or Celeron processor. It is the heart of
every PC. All scheduling, computation and control occurs
here.
- BIOS - Basic Input Output System is a non-volatile
memory that contains configuration information
about the PC. It contains all the code required for the CPU to
communicate with the keyboard, mouse video display, disk drives
and communications devices.
When a PC is powered on it uses the BIOS 'boot code' to set
up many required functions that bring the PC to a point
where it is ready to work.
- RTC - the Real Time Clock chip keeps date, day
and time in a 24 hour format just like your watch. The PC
uses this clock to 'time stamp' files as they are created
and modified. When you print a file it time stamps the
pages as they are printed.
- Chip Set - these are large chip(s) that
integrate many functions that used to be found in separate
smaller chips on the motherboard. They save space and cost.
The functions performed by these chip sets often broken
into two devices with one providing an interface from the
CPU to the memory and the other providing controllers for
IDE, ISA, PCI and USB devices (see below).
Primary Connectors found on the motherboard are:
Since this web site first went online the PC has changed a lot
and some of the connectors, once a mainstay of the PC have been
replaced. They are left in for historical purposes and are identified
as 'now obsolete'.
- Power - A 24 pin connector accepts a plug from
the power supply. This plug carry DC power to all the circuits
on the motherboard.
- Ethernet - An 8-pin connector commonly referred to as an
RJ-45 connector accepts communications cables which connect the PC to
routers and ultimately modems which carry Ethernet encapsulated data
to/from the PC through the Internet to remote servers.
- Keyboard - A Mini-din 6-pin (round) connector
found at the back of the motherboard is where a PS/2 type keyboard
can plug in.
This connector is retained in some newer motherboards although
most keyboards now connect to the PC via a USB port.
- Mouse - A Mini-din 6-pin connector found next to
the keyboard connector is where the where a PS/2 type mouse
can plug in.
This connector is retained in some newer motherboards although
the mouse now usually connects to the PC via a USB port.
- Display - The video drivers is integrated in
the motherboard and provided to the monitor at the back
of the board via 15-pin D shell connector.
In early model PCs the display function
was found in a video card that plugged into the AGP connector
of the motherboard which provided the video signal to the
monitor via 15-pin D-shell connector located at the back
of the video card.
- SATA - stands for Serial ATA Integrated Drive Electronics.
SATA is an internalcomputer bus interface that supports both Serial ATA (SATA)
devices (newer hard drives) and PCI Express (PCIe) storage devices
- Memory Slots - Internal connectors are provided
for DIMM (Dual in line module) modules that contain 8 or more
DRAM (Dynamic Random Access Memory) chips which collectively
provide memory for the PC uses in operation.
- HDMI - Some PCs provide HDMI (high definition multimedia interface)
connectors used by on board display controllers to send uncompressed
video data and compressed or uncompressed digital audio data to a
compatible computer monitors, video projectors, digital televisions,
or digital audio device.
- IDE - (now obsolete) stands for Integrated Drive Electronics.
These are 40 pin connectors that provide a place to connect
the ribbon cables from the drives (hard and CD/DVD). All data
between the motherboard and the drives is carried in these
cables. They are not accessible unless the PC cover is
removed.
IDE has been replaced by the SATA connectors in new PCs.
- FDD connector - (now obsolete) it is similar in function to the
IDE connector. It is a 34 pin ribbon connector that carries
data between the motherboard and any floppy drive installed
in the PC. Not accessible with PC cover on.
- Serial Connectors
- USB - Universal Serial Bus USB version 1.1 was first released
in 1999 with two speeds: low speed 1.2Mb/s and full speed at 12Mb/s.
The latest version 3.1 released in 2013 moves data over 800 times faster at 10 Gb/s.
USB has the capability in some designs to power devices
connected to it. The devices must be low
power devices and must be able to reduce their current draw
to less than 0.5uAmps when commanded to do so by the PC.
USB is now a standard connector on all new
motherboards and has effectively replaced the standard serial
port that had been the workhorse serial port in earlier PCs.
- Standard Serial Port - (now obsolete)
This port has been around in PCs since they first appeared. It was
originally located on ISA expansion type cards and eventually
became an integral part of newer motherboards. It uses a 9-
pin, D-shell connector that allows you to connect external
devices with serial ports to your PC. The maximum data rate
is 115 KB/s.
- Parallel Connectors
Both connectors in this category are effectively obsolete as
most I/O devices now use USB to connect to the PC.
- Centronix or Standard Parallel - (now obsolete)This connector
has been around in PCs since they first appeared. It has
37-pins and is now integrated on new motherboards. It is
usually used to connect your printer to the PC and moves
data at about 1MB/s.
- SCSI - (now obsolete)Small Computer System Interface moves
data at a maximum of up to 80Mb/s. It not integrated into
most PC motherboards. It can be added to a PC as an
Expansion card (see below). Some printers and hard disk
drives use SCSI interfaces.
- Expansion Card Connectors - The CPU connects to
expansion card connectors through one of the chip set ICs
mentioned above. They are located on the motherboard near
the rear of the PC. These connectors allow special function
cards to plug into and work with the PC.
Before motherboards integrated the serial and centronix
connectors they were found on expansion boards that plugged
into ISA slots.
Most PCs have the following expansion connector types:
- PCI - Peripheral Component Interconnect is a
newer and faster interface that accepts all expansion cards
that have a PCI interface.
- AGP - Accelerated Graphics Port is a connector
that is designed to work with video cards. Your video display
plugs into and is controlled by one of these video cards.
Many modern video cards offer enhanced 3D-graphics and fast, full
motion video.
- ISA - (now obsolete) Industry Standard Architecture connectors
have been around since 1980 and first appeared in the IBM
XT PC. This type of slot still appears on some newer
motherboards so that older expansion boards can still be
used. However, many motherboards no longer have ISA connectors
on them.
Contact Information
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