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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.



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