What is a Motherboard?

The Motherboard is the main circuit board inside the PC. It holds the CPU and memory, provides expansion slots for peripherals, and, whether directly or indirectly, connects to every part of the PC.
The essential motherboard make-up includes the chipset (known as the “glue logic”), some code in ROM and the various wired interconnections between the components know as buses. The chipset is fundamental, and controls how the motherboard interacts with everything else in the system. A good chipset can be more important than the power of CPU or the amount of RAM. The ROM code includes the BIOS, which has user-changeable options for how the motherboard operates with integral and connected devices. The buses are the electrical wires that connect everything together.
Motherboard designs use many different buses to link their various components. For instance, wide, high-speed buses are difficult and expensive to produce. The signals travel at such a rate that even distances of just a few centimetres cause timing problems, while the metal tracks on the circuit board act as miniature radio antennae, transmitting electromagnetic noise that introduces interference with signals elsewhere in the system. For these reasons, design engineers try to keep the fastest buses confined to the smallest area of the motherboard and use slower, more robust buses for other parts.

Types of Slots on a Motherboard

Motherboards are the backbone of a computer, holding different vital parts such as the processor, RAM and also providing connections to other peripherals. Upgrading internal computer parts is always an option if programs on your computer are running sluggishly or if software is incompatible due to a lack of resources. This can be especially true if you require high-end graphics or video editing programs. To upgrade you will need to know the types of slots on the motherboard and whether replacement parts will fit.
CPU Slot

The CPU is often called the brains of a computer because it is the hardware that carries out instructions from software by using math, input/output commands and logic. The CPU slot (also known as a CPU socket) is where the processor is stored on a computer's motherboard. To replace a CPU you will need to raise the socket by lifting a small lever on the side of the socket; then you can gently pull out the CPU hardware. Replace the old CPU with a new one by aligning your new CPU with the socket, gently placing it in (do not push) and then flipping the socket lever to secure it.
RAM Slot

Random access memory (RAM) is data storage hardware on your computer's motherboard. Despite the name, RAM does not actually "remember" anything when a computer is turned off. Programs must be saved on the hard drive or another storage device. In practical terms, RAM determines how many programs can run at once and how large the programs can be. Computers cannot run without RAM installed. They often come packaged with multiple strips located in RAM slots on the motherboard that are easily removable and replaceable. Upgrading RAM will improve the speed of your computer.
The Peripheral Component Interconnect (PCI) slot is a slot for expansion devices. Most desktop computers come with several PCI expansion slots. PCI slots are used for a variety of devices: modems, network cards, television tuners, radio tuners, video cards and sound cards, among others. Most computers today have several of these cards already built in. For computers that do not, these expansion devices provide additional functionality to a computer, making it possible for essential functions in a business such as wireless Internet connectivity.
PCI Express Slot

The PCI Express slot, like the PCI slot, is used for expansion cards. PCI Express allows for higher transfer speeds than PCI and is therefore preferred for graphics cards. The PCI Express has replaced the Accelerated Graphics Port (AGP) in most computers as the primary slot for graphics cards. Many newer programs, such as Adobe's popular photo and video editors, rely more on an advanced graphics card to process data. Upgrading your graphics card can improve performance markedly.
What is a chipset “Chipset” is the name given to the set of chips (hence its name) used on a motherboard.
In the first PCs, the motherboard used discrete integrated circuits. Therefore, many chips were needed to create all the necessary circuitry to make the computer work. In Figure 1, you can see a motherboard from a PC XT clone.

Figure 1: PC XT clone motherboard
After some time, chip manufacturers started to integrate several chips into larger chips. Instead of requiring dozens of small chips, a motherboard could now be built using only a half-dozen big chips.
Around the mid-1990s, motherboards using only two or even one big chip could be built. In Figure 2, you can see a motherboard for 486-class CPUs circa 1995 using only two big chips with all necessary functions to make the motherboard work.
Figure 2: A motherboard for 486-class CPUs; this model uses only two big chips
With the release of the PCI bus, a new concept, which is still used nowadays, could be used for the first time: the use of bridges. Usually, motherboards have two big chips: the north bridge and the south bridge. Sometimes, some chip manufacturers can integrate the north and south bridges into a single chip; in this case, the motherboard will have just one big integrated circuit. Or, depending on the CPU architecture, it may require only the south bridge chip.
In the past, several different companies provided chipsets for the PC. Nowadays, however, only Intel, AMD, and VIA are still manufacturing chipsets, and they only design products for motherboards that will use their CPUs. (VIA also used to design chipsets for CPUs from both Intel and AMD.) Other companies that used to manufacture chipsets include ATI, NVIDIA, VIA, SiS, ULi/ALi, UMC, and OPTi.
A common confusion is to mix the chipset manufacturer with the motherboard manufacturer. For example, because a motherboard uses a chipset manufactured by Intel does not mean that Intel manufactured this board. ASUS, Gigabyte, MSI, ECS, ASRock, Biostar, and also Intel are just some of the many motherboard manufacturers present on the market. So, the motherboard manufacturer buys the chipsets from the chipset manufacturer and builds motherboards.

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What is the difference between BIOS and CMOS?
The BIOS and CMOS are often times thought to be the same thing, but they are not. They are two different components of a computer, but they do work together to make the computer function properly.

The BIOS is a computer chip on the motherboard that resembles the picture to the right. This chip contains a special program that helps the computer processor interact and control the other components in the computer. These other components includedisc drives, video cards, sound cards, network cards, floppy drives, USB ports, hard drives, and others. Without the BIOS, the processor would not know how to interact or interface with the computer components, and the computer would not be able to function.
The CMOS is also a computer chip on the motherboard, but more specifically, it is a RAM chip. This is a type of memory chip which stores information about the computer components, as well as settings for those components. However, normal RAM chips lose the information stored in them when power is no longer supplied to them. To retain the information in the CMOS chip, a CMOS battery on the motherboard supplies constant power to that CMOS chip. If the battery is removed from the motherboard or runs out of juice (e.g. a dead CMOS battery), the CMOS changes again after a new CMOS battery was put on the motherboard. For example, with a dead CMOS battery the time and date will reset back to the manufactured date if it has been off for a long period of time.
The BIOS program on the BIOS chip reads information from the CMOS chip when the computer is starting up, during the boot up process. You may notice on the initial start up screen, called the POST screen, an option is available to enter the BIOS or CMOS setup. When you enter this setup area, you are entering the CMOS setup, not the BIOS setup. The BIOS chip and program cannot be updated directly by a user. The only way to update the BIOS is using a BIOS flash program called a BIOS update, which updates the BIOS to a different version. These updates usually are provided by either the motherboard manufacturer or the computer manufacturer.
The CMOS setup lets you change the time and date and settings for how devices are loaded at start up, like hard drives, disc drives, and floppy drives. The CMOS setup lets you enable and disable various hardware devices, including USB ports, the onboard video card and sound card (if present), parallel and serial ports, and other devices.

The I/O ports and connectors on your system are the gateways through which the system communicates with external devices such as a keyboard, mouse, and monitor. Figure B-1 identifies back-panel I/O ports and connectors. Figure B-2 identifies front-panel I/O ports and connectors.
Figure B-1. Back-Panel I/O Ports and Connectors

Figure B-2. Front-Panel I/O Ports and Connectors

Serial Ports
The integrated serial ports use 9-pin D-subminiature connectors on the back panel. These ports support devices such as external modems, printers, plotters, and mice that require serial data transmission (the transmission of data one bit at a time over one line).
Most software uses the term COM (for communications) plus a number to designate a serial port (for example, COM1 or COM2). The default designations of your system's integrated serial ports are COM1 and COM2.
Serial Port Connector
If you reconfigure your hardware, you may need pin number and signal information for the serial port connector. Figure B-3 illustrates the pin numbers for the serial port connector and Table B-1 defines the pin assignments and interface signals for the serial port connector.
Figure B-3. Pin Numbers for the Serial Port Pin | Signal | I/O | Definition | 1 | DCD | I | Data carrier detect | 2 | SIN | I | Serial input | 3 | SOUT | O | Serial output | 4 | DTR | O | Data terminal ready | 5 | GND | N/A | Signal ground | 6 | DSR | I | Data set ready | 7 | RTS | O | Request to send | 8 | CTS | I | Clear to send | 9 | RI | I | Ring indicator | Shell | N/A | N/A | Chassis ground |

Table B-1. Serial Port Pin Assignments
Adding an Expansion
Card Containing Serial or Parallel Ports
The system has an autoconfiguration capability for the serial ports. This feature lets you add an expansion card containing a serial port that has the same designation as one of the integrated ports, without having to reconfigure the card. When the system detects the duplicate serial port on the expansion card, it remaps (reassigns) the integrated port to the next available port designation.
Both the new and the remapped COM ports share the same IRQ setting, as follows:
COM1, COM3: IRQ4 (shared setting)
COM2, COM4: IRQ3 (shared setting)
These COM ports have the following I/O address settings:
COM1: 3F8h
COM2: 2F8h
COM3: 3E8h
COM4: 2E8h
For example, if you add an internal modem card with a port configured as COM1, the system then sees logical COM1 as the address on the modem card. It automatically remaps the integrated serial port that was designated as COM1 to COM3, which shares the COM1 IRQ setting. (Note that when you have two COM ports sharing an IRQ setting, you can use either port as necessary but you may not be able to use them both at the same time.) If you install one or more expansion cards with serial ports designated as COM1 and COM3, the corresponding integrated serial port is disabled.
Before adding a card that remaps the COM ports, check the documentation that accompanied your software to make sure that the software can be mapped to the new COM port designation.
To avoid autoconfiguration, you may be able to reset jumpers on the expansion card so that the card's port designation changes to the next available COM number, leaving the designation for the integrated port as is. Alternatively, you can disable the integrated ports through the System Setup program. The documentation for your expansion card should provide the card's default I/O address and allowable IRQ settings. It should also provide instructions for readdressing the port and changing the IRQ setting, if necessary.
For general information on how your operating system handles serial and parallel ports, and for more detailed command procedures, see your operating system documentation.

Keyboard and Mouse Connectors
The system uses a PS/2-style keyboard and supports a PS/2-compatible mouse. Cables from both devices attach to 6-pin, miniature DIN connectors on the front and back panels of your system. | NOTE: To enable the front-panel PS-2 connector, a monitor must be connected to the front-panel video connector. When a monitor is connected to the front panel, the back-panel keyboard, mouse, and video are all disabled. |

| NOTE: To connect a keyboard and mouse to the front of the system, either use a PS/2 Y adapter to connect both a keyboard and mouse to the PS/2 connector, or use a PS/2 keyboard and a USB mouse. |
Mouse driver software can give the mouse priority with the microprocessor by issuing IRQ12 whenever a new mouse movement is detected. The driver software also passes along the mouse data to the application program that is in control.
Keyboard Connector
If you reconfigure your hardware, you may need pin number and signal information for the keyboard connector. Figure B-4 illustrates the pin numbers for the keyboard connector. Table B-2 and Table B-3 defines the pin assignments and interface signals for the keyboard connector.
Figure B-4. Pin Numbers for the Keyboard Connector

Table B-2. Keyboard Connector Pin Assignments (Back Panel) Pin | Signal | I/O | Definition | 1 | KBDATA | I/O | Keyboard data | 2 | NC | N/A | No connection | 3 | GND | N/A | Signal ground | 4 | FVcc | N/A | Fused supply voltage | 5 | KBCLK | I/O | Keyboard clock | 6 | NC | N/A | No connection | Shell | N/A | N/A | Chassis ground |
Table B-3. Keyboard/Mouse Combination Connector
Pin Assignments (Front Panel) Pin | Signal | I/O | Definition | 1 | KBDATA | I/O | Keyboard data | 2 | MSDATA | I/O | Mouse data | 3 | GND | N/A | Signal ground | 4 | FVcc | N/A | Fused supply voltage | 5 | KBCLK | I/O | Keyboard clock | 6 | MSCLK | I/O | Mouse clock | Shell | N/A | N/A | Chassis ground |
Mouse Connector
The following is pin information for the mouse connector. If you reconfigure your hardware, you may need pin number and signal information for the mouse connector. Figure B-5 and illustrates the pin numbers for the mouse connector. Figure B-5and Table B-4 defines the pin assignments and interface signals for the mouse connector.
Figure B-5. Pin Numbers for the Mouse Connector

Table B-4. Mouse Connector Pin Assignments (Back Panel) Pin | Signal | I/O | Definition | 1 | MSDATA | I/O | Mouse data | 2 | NC | N/A | No connection | 3 | GND | N/A | Signal ground | 4 | FVcc | N/A | Fused supply voltage | 5 | MSCLK | I/O | Mouse clock | 6 | NC | N/A | No connection | Shell | N/A | N/A | Chassis ground |

Video Connectors
The system uses a 15-pin high-density D-subminiature connector on the front and back panels for attaching a VGA-compatible monitor to your system. The video circuitry on the system board synchronizes the signals that drive the red, green, and blue electron guns in the monitor.
Guidelines
| NOTE: When a monitor is connected to the front panel, the back-panel keyboard, mouse, and video are all disabled. | * This system provides two video connectors, one on the back panel, and one on the front panel. If the monitor is connected to the front-panel video connector, the back-panel video connector is disabled. * The keyboard and mouse must be connected to the same panel as the monitor. For example, if the monitor is connected to the front-panel video connector, the keyboard and mouse must also be connected to the keyboard/mouse front-panel connector. This connector is a PS/2 connector and the keyboard connection is the default. To use both the keyboard and mouse from the front-panel connector, you must use a Y-cable.
If you reconfigure your hardware, you may need pin number and signal information for the video connector. Figure B-6 illustrates the pin numbers for the video connector, and Table B-5 defines the pin assignments and interface signals for the video connector.
Figure B-6. Pin Numbers for the Video Connector

Table B-5. Video Connector Pin Assignments Pin | Signal | I/O | Definition | 1 | RED | O | Red video | 2 | GREEN | O | Green video | 3 | BLUE | O | Blue video | 4 | NC | N/A | No connection | 5–8, 10 | GND | N/A | Signal ground | 9 | VCC | N/A | Vcc | 11 | NC | N/A | No connection | 12 | DDC data out | O | Monitor detect data | 13 | HSYNC | O | Horizontal synchronization | 14 | VSYNC | O | Vertical synchronization | 15 | DDC clock out | O | Monitor detect clock | Shell | N/A | N/A | Chassis ground |

USB Connectors
Your system contains a single USB connector on the front control panel, and two USB connectors on the rear panel for attaching USB-compliant devices. USB devices are typically peripherals such as mice, keyboards, and system speakers. | NOTICE: Do not attach a USB device or a combination of USB devices that draw a maximum current over 500 mA per channel on +5 V. Attaching devices that exceed this threshold may cause the USB ports to shut down. See the documentation that accompanied the USB devices for their maximum current ratings. |
If you reconfigure your hardware, you may need pin number and signal information for the USB connectors. Figure B-7 illustrates the USB connector and Table B-6 defines the pin assignments and interface signals for the USB connector.
Figure B-7. Pin Numbers for the USB Connector

Table B-6. USB Connector Pin Assignments Pin | Signal | I/O | Definition | 1 | Vcc | N/A | Supply voltage | 2 | DATA- | I/O | Data | 3 | DATA+ | I/O | Data | 4 | GND | N/A | Signal ground |

Integrated NIC Connectors
Your system has two integrated 10/100/1000–Mbps NICs. The 10/100/1000-Mbps NICs provide faster communication between servers and workstations and efficient utilization of host resources, freeing more of the system resources for other applications. Both NICs support 10 Base-T, 100 Base-TX, and 1000 Base-T Ethernet standards.
Both NICs include a Wake On LAN feature that enables the system to be started by a special LAN signal from a systems management console. Wake On LAN provides remote system setup, software downloading and installation, file updates, and asset tracking after hours and on weekends when LAN traffic is typically at a minimum.
Network Cable Requirements
Your system's RJ45 NIC connectors are designed for attaching a UTP Ethernet cable equipped with standard RJ45-compatible plugs. Press one end of the UTP cable into the NIC connector until the plug snaps securely into place. Connect the other end of the cable to an RJ45 jack wall plate or to an RJ45 port on a UTP concentrator or hub, depending on your network configuration. Observe the following cabling restrictions for 10 Base-T, 100 Base-TX, and 1000 Base-T networks. | NOTICE: To avoid line interference, voice, and data lines must be in separate sheaths. | * Use Category 5 or greater wiring and connectors. * The maximum cable run length (from a system to a hub) is 328 ft (100 m). * You can find guidelines for operation of a network can be found in "Systems Considerations of Multi-Segment Networks" in the IEEE 802.3 standard.
Figure B-8. NIC LEDs