| -- End Ad Box ---> | | | | Play (PnP) to solve this problem. One of the main |
| Your computer has many devices connected to it. | | | | structures supporting PnP is the Peripheral |
| Your key board is a device. Your mouse is a | | | | Component Interconnect (PCI) bus. Along with a |
| device. Your modem is a device. Even a port, like | | | | PCI bus, the computers BIOS, operating system, |
| a USB port, is a device. You can add a device to | | | | and hardware devices must be PnP compliant. |
| your computer by installing it into an expansion | | | | One of the key features of PnP is that when |
| connector on the the motherboard of the | | | | installing a PCI card, you do not need to use |
| computer. In order to operate, resources need to | | | | jumpers of DIP switches to set the IRQ or I/O |
| be allocated to the device. | | | | address for the card, the PCI bus controller does |
| One of the most important resources a device | | | | this for you. |
| needs is an Interrupt Request (IRQ) line. An IRQ | | | | The Windows 2000/XP operating system |
| signals the processor that the device needs | | | | component responsible for PnP is the Advanced |
| attention. For example, each time you press a | | | | Configuration and Power Interface (ACPI). ACPI |
| key on your keyboard, an IRQ is sent to let the | | | | allows devices to be controlled by the operating |
| processor know that the keyboard needs | | | | system to perform power management. ACPI |
| attention. A device also needs to be allocated a | | | | may put a device in a power saving state such as |
| set of memory addresses where commands can | | | | Standby, Suspend or Off. ACPI also allows |
| be sent to it and it can send responses. | | | | dynamic handling of events like the addition or |
| Many devices need to be allocated an area of | | | | removal of a USB device. |
| memory to store data and/or a Direct Memory | | | | During the boot process, the BIOS builds a table |
| Access (DMA) channel. A DMA channel allows a | | | | to record which IRQs have been used by legacy |
| device to create a data stream directly between | | | | ISA devices and then assigns the unused ones to |
| it and the computers memory without passing | | | | the PCI bus controller. The PCI bus controller, |
| through the processor. | | | | which is part of the motherboard chip set, |
| One of the most important structures in a | | | | manages the PCI bus and the expansion slots. |
| computer is the system bus located on the | | | | Each PCI device communicates its resource |
| motherbord. The processor, chipset, memory, and | | | | requirements to ACPI. Based on the resource |
| expansion slot devices communicate over the bus. | | | | requests that each device makes, ACPI assigns |
| Early PCs used a bus called Industry Standard | | | | resources such as IRQs, I/O addresses, and |
| Architecture (ISA). When you installed an | | | | memory locations, and DMA channels. ACPI can |
| expansion card into the ISA bus, you had to set | | | | reconfigure resource assignments when needed, |
| IRQs and other resources with jumpers and/or | | | | for example, when a device is added to the |
| DIP switches on the card. ISA devices cannot | | | | system. |
| share resources, each ISA device must have its | | | | The PCI bus overcomes the limitation in available |
| own IRQ. | | | | IRQ's with a feature called "PCI steering". PCI |
| - You can have more than one ISA device | | | | steering makes it possible for several devices to |
| configured for the same IRQ, as long as only one | | | | use the same IRQ. PCI steering allocates an IRQ |
| of the device drivers is loaded at any one time; | | | | called the "IRQ Holder" for PCI steering. The PCI |
| otherwise, you'll get an IRQ conflict. | | | | controller steers that IRQ to its own interrupt |
| Since a computer has only a limited amount of | | | | systems on the PCI bus. These interrupts are |
| resources, the number of devices that a | | | | called A, B, C, D, and so on to avoid confusion |
| computer could support is limited. One of the | | | | with the numbered system IRQs. One interrupt is |
| most limited resources is IRQ lines. A PC has only | | | | assigned to each PCI expansion slot. |
| 16 IRQs. Common devices such as the keyboard, | | | | To see which IRQ has been assigned to the IRQ |
| mouse, floppy drive, and hard drive use a | | | | Holder for PCI steering, open the Control Panel |
| standard set of resources. | | | | "System" utility. In the "System Properties" dialog |
| Standard IRQ aassignments | | | | box, select the "Hardware" tab and click on the |
| IRQ DEVICE | | | | "Device Manager..." button. In Device Manager's |
| 0 System Timer | | | | "View" menu select "Resources by type", then |
| 1 Keyboard | | | | open the "Interrupt request IRQ" branch.pcirq.bmp |
| 2 IRQ Controller 2 | | | | - Note that Windows 2000 uses IRQ 9 for PCI |
| 3 COM2 | | | | Steering, so never set a device to IRQ 9. |
| 4 COM1 | | | | PnP resource allocation removes the need to use |
| 5 LPT2 | | | | jumpers of DIP switches to set the IRQ and |
| 6 Floppy Drive | | | | other resources for devices. But PnP involves a |
| 7 LPT1 | | | | complex interaction between the computers |
| 8 Real-Time Clock | | | | BIOS, chipset, PCI bus, operating system, and PnP |
| 9 ACPI | | | | devices. |
| 10 unallocated | | | | Copyright(C)2004 Bucaro TecHelp. |
| 11 IRQ Holder | | | | Permission is granted for the below article to |
| 12 Mouse | | | | forward, reprint, distribute, use for ezine, |
| 13 Math Coprocessor | | | | newsletter, website, offer as free bonus or part |
| 14 Primary IDE | | | | of a product for sale as long as no changes are |
| 15 Secondary IDE | | | | made and the byline, copyright, and the resource |
| In 1993, Microsoft and Intel developed Plug and | | | | box below is included. |