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motherboard is the central printed circuit board (PCB) in many modern computers and holds many of the crucial components of the system, providing connectors for other peripherals.

The motherboard is sometimes alternatively known as the mainboard, system board, or, on Apple computers, the logic board. It is also sometimes casually shortened to mobo.

Major Components found on the motherboard are

CPU - The central processing unit (CPU) is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. On large machines, CPUs require one or more printed circuit boards.

On personal computers and small workstations, the CPU is housed in a single silicon chip called a microprocessor. Since the 1970s the microprocessor class of CPUs has almost completely overtaken all other CPU implementations. Modern CPUs are large scale integrated circuits in packages typically less than four centimeters square, with hundreds of connecting pins.

Two typical components of a CPU are the arithmetic logic unit (ALU), which performs arithmetic and logical operations, and the control unit (CU), which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.
With faster processors the clock speed becomes more important. Compared to some of the first computers which operated at below 30 megahertz (MHz) the Pentium chips began at 75 MHz in the late 1990's. Speeds now exceed 3000+ MHz or 3 gigahertz (GHz) and different chip manufacturers use different measuring standards (check your local computer store for the latest speed). It depends on the circuit board that the chip is housed in, or the motherboard, as to whether you are able to upgrade to a faster chip. The motherboard contains the circuitry and connections that allow the various components to communicate with each other.

BIOS - The basic input/output system (BIOS), also known as the System BIOS or ROM BIOS.  The BIOS software is built into the PC, and is the first code run by a PC when powered on ('boot firmware'). When the PC starts up, the first job for the BIOS is the power-on self-test, which initializes and identifies system devices such as the video display card, keyboard and mouse, hard disk drive, optical disc drive and other hardware. The BIOS then locates boot loader software held on a peripheral device (designated as a 'boot device'), such as a hard disk or a CD/DVD, and loads and executes that software, giving it control of the PC. This process is known as booting, or booting up, which is short for bootstrapping. 

BIOS software is stored on a non-volatile ROM chip on the motherboard. It is specifically designed to work with each particular model of computer, interfacing with various devices that make up the complementary chipset of the system. In modern computer systems the BIOS chip's contents can be rewritten without removing it from the motherboard, allowing BIOS software to be upgraded in place.

A BIOS has a user interface (UI), typically a menu system accessed by pressing a certain key on the keyboard when the PC starts. In the BIOS UI, a user can:
  • configure hardware
  • set the system clock
  • enable or disable system components
  • select which devices are eligible to be a potential boot device
  • set various password prompts, such as a password for securing access to the BIOS UI functions itself and preventing malicious users from booting the system from unauthorized peripheral devices.

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.

    Primary Connectors found on the motherboard are:
    • Power - A 20 pin connector accepts a plug from the power supply. This plug carry DC power to all the circuits on the motherboard. 
    • Keyboard - A Mini-din 6-pin (round) connector found at the back of the motherboard is where the keyboard plugs in. 
    • Mouse - A Mini-din 6-pin connector found next to the keyboard connector is where the where the mouse plugs in. 
    • Display - This connector is not integrated into the motherboard but is included in this list since its function is absolutely necessary. It is a 15-pin, D-shell type connector found on a video card that plugs into the AGP connector of the motherboard. 
    • IDE - 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. 
    • FDD connector - 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. 
    • DRAM - Dynamic Random Access Memory connectors for SIMM and DIMM type memory modules. Not accessible with chassis cover on. 

    Serial Connectors:

    Standard Serial Connector - This connector has been around in PCs since they first appeared. It was originally located on ISA expansion type cards. Today it is an integral part of newer motherboards. It is 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.  

    USB - Universal Serial Bus This is a relatively new serial bus. Originally specified as low speed, 1.2 Mb/s, it was enhanced to full speed, 12Mb/s. The latest version 2.0 is specified as high speed, 400 MB/s. Someday USB will completely replace the standard serial connector that has been the workhorse serial port in earlier PCs. USB is now a standard connector on all new motherboards. 

    Unlike serial and parallel ports, the USB port is designed 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. 

    Parallel Connectors:

    Centronix or Standard Parallel - 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 - 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. 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. 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:

        ISA - 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.

        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.

        Last updated on: 02/10/2019


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