About->>Motherboard
Motherboard:
The motherboard is, without a doubt, the primary component of the entire system. Without the support circuitry and functions this device provides, even the CPU is unable to work. A motherboard also known as main board, logic board, or system board. Typically the motherboard contains slots, and all the controllers required to control standard peripheral devices, such a display screen, keyboard and disk drive etc.
In addition to the hardware, the motherboard also contains some software. The system ROM actually contains three small, but very critical programs. These are the POST, the BIOS and the setup program. Power on Self Test (POST) is the program that initializes and tests each components of the motherboard every time it starts up to make sure everything is ready to run. The Basic I/O Service (BIOS) is a collection of very small programs that enable the system to communicate with hardware devices during the boot process. Finally the setup program is used to configure the features found on the motherboard.
Important component of the motherboard:
1. Chipsets:
Chipset is made up of one or more electronic components that connects the motherboard components such as, the processor, expansion and internal memory. Basically the work of the chipset is to control the system and its capabilities. Chipset determines the speed of the motherboard. It is also responsible for increasing the speed of the communication between processor and the peripheral devices. Mostly used chipset in the computer motherboard is Northbridge chip and Southbridge chip. Northbridge chip is the name given to the system controller chip. This is the chip that directly connects the CPU’s front side bus (FSB) to the high speed components of the system, which would include RAM, the AGP port and all other high speed peripherals. The FSB (also known as the external data bus) of the CPU must be able to synchronize with all the other devices. Where as the Southbridge chip is slower than the Northbridge chip. Southbridge chip is the component of the chipset that is responsible for interconnecting the CPU’s FSB to the slower component of the system. Device managed by this chip include IDE port, USB ports, the ISA bus and other devices that are not supported by the super I\O chip. The information from the CPU has to go through the Northbridge chip before reaching the Southbridge chip.
2. Microprocessor:
Microprocessor is one of the main components of the motherboard. It is a square shaped chip installed on the motherboard and performs the operations like subtraction, addition, multiplication and division on the data and sends out the results. It also performs logical and comparison operations on data. Moreover, the microprocessor controls the activities of various components of the computer and also responds to the requests from the peripheral devices e.g printer signals indicating that it has run out of paper.
3. Clock Chip:
Clock chip is a small chip on the motherboard used as a timekeeper for the components of a computer, which are designed to operate in perfect synchronization. The chip provide the timing signal in the form of electronic pulses that are used by the computer components to set up a working pace. The clock speed of PCs ranges from a low of 16MHz to a high of 500MHz. The clock speed is one way to measuring the speed of a computer. Another unit for measuring the speed of a computer is MIPS (Million Instructions per second). It gives the number of instructions executed per second.
4. Bus:
A bus is simply a circuit that connects one part of the motherboard to another. The speed of the bus is measured in megahertz (MHz). The communication between the microprocessor and the memory chips as well as the other chips found on the motherboard is accomplished through a bus. The bus comprising of 8 wires for carrying data is called the data bus. When data is sent from one unit to another, the address (location in memory at which the data is stored) is also send with the data. The bus has a set of 20 wires for carrying the address. This type of bus is called the address bus. Bus speed usually refers to the speed of the Front Side Bus (FSB), which connects the CPU to the Northbridge. FSB speeds can range from 66 MHz to over 800 MHz.
5. Ports, sockets and memories:
Moreover the motherboard also contains some ports (like serial and parallel port) for connecting the peripheral devices to the computer motherboard. Motherboard also contains some sockets in which the main memory is placed.
Motherboard controller and system resources:
System resources are resources that are electrically used by hardware, allocated by firmware, and used by software for each device. In some ways, everything in a PC is a resource of system like RAM, processor speed, hard disk space, etc. But there are several special resources in the system that are shared by the various devices that use it. These are not physical "parts" of the system. Rather they are logical parts of the system that control how it works, and are referred to as the PC's system resources. System resources are important because they must be shared by the various devices in your PC. This includes not only the motherboard and other main components, but also expansion devices, plug-in cards and peripherals. The resources are primarily used for communication and information transfer between these devices.
Some of the system resources are given below:
Memory Address: Some devices require some space in the memory area for their own use. The devices that use a memory area generally use it for their own BIOS, which contain code to control the device and is invoked by direct calls or calls from the internal system BIOS.
Input/output Ports: Every device must have at least one I/O port to send data and commands to and from the device.
IRQ Line: Many devices use this resource type, but not all. Usually, if a device is designed to perform tasks independent of the CPU, it will need an IRQ line to alert the CPU when a task is done or attention is needed. A mouse and a network card are examples of devices that always use an IRQ.
DMA Channels: The DMA channels were originally designed to take advantages of faster transfers of data to and from memory using a DMA controller instead of the CPU. As CPU increased, however, DMA channel resources usage decreased, because the CPU was actually faster than DMA.
Memory Address:
There are a few devices that need to allocate memory addresses as a system resource for their own use. The most common add-in device to use a dedicated memory address space for its own BIOS is a SCSI host adapter. In addition, network cards that have the ability to boot the computer over the network typically also use a memory area for the boot BIOS. But fortunately there are very less conflicts in this area today. Most commonly used memory conflict in the case of memory address is that sometimes the two video adapter cards or other devices using the same memory address locations. The best method to overcome this problem is to draw a memory map which clearly show that which memory address location is assigned to which device.
I\O ports:
Every device in every PC uses at least one I\O port address, in most cases, a single device uses 4, 8, or 16 I\O port address. These port addresses are used to do the following:
1. Send commands to the device.
2. Get device information and status.
3. Set, check and clear device interrupts.
4. Send and receive data.
I\O port conflicts are usually only a problem with the older ISA cards, although they can also be a problem with devices that are integrated directly on the motherboard with their own connections to the ISA bus. Newer ISA cards that are PnP compatible can be automatically reconfigured by the operating system and therefore are not usually involved in conflicts.
I\O port conflicts are quite similar to memory address conflicts. In fact, the I\O address signals are actually carried on the same wires as the memory address bus, with one additional wire used by the CPU to tell the rest of the system that it is an I\O operation and not a memory operations. This is usually refers as IO/MEM wire.
IRQ Lines:
IRQ stands for Interrupt Request. An interrupt is an unavoidable task or command provided by the device of computer to the system processor. When the processor get such type of interrupt it stop the execution of the instructions of the current task and starts working on the interrupt. The purpose of the IRQ lines is to get the CPU’s attention when it is needed. Not all devices use interrupts, and some devices use interrupts only is certain cases. Interrupts are widely used during the modem communication. Interrupts are not provided by the CPU, it is provided by a special chip.
The reaction of the system when it got the interrupt is given below:
- The IC chip on the motherboard sees the IRQ and passes it on to the CPU if there are no other interrupt in progress, or pending IRQs of higher priority.
- When the CPU sees an IRQ, it stops the foreground task at the end of the current instruction and saves the location of the next instruction to be run for the foreground task and starts working on interrupt.
- When the interrupt finishes the foreground task continues with the next instruction it had saved and all the internal registers back to the way they were before the interrupt.
The original PC had eight IRQ lines, of which six were usable. Starting with the AT computers and all PCs since, there are 16 IRQ lines of which 11 are usable. IRQ2 and IRQ9 are two names for the same wire, and can conflict with each other, no IRQs can conflict with other IRQs of a different number.
Interrupts are actually provided not by the CPU, but a separate IC chip that can prioritize eight different IRQ lines coming in and pass them on to the CPU, queuing them up if needed. On the original IBM PC, the 8259 IRQ controller chip handled this task. Because IRQ0 and IRQ1 were dedicated to motherboard functions, only six IRQs were actually available to other devices
When the AT computer came out, IBM added a second 8259 IRQ controller chip to the motherboard, which was cascaded through the first one which is shown below.
As you can see from the diagram that the cascading of the first 8259 IRQ controller chip and second 8259 IRQ controller chip is carried out through the IRQ2 line of first 8259 and IRQ9 line of second IRQ controller chip. Therefore the conflicts generate between the IRQ2 and IRQ9
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