Plug,and,Play,Resource,Allocat computer Plug and Play Resource Allocation

----------------------------------------------------------Permission is granted for the below article to forward,reprint, distribute, use for ezine, newsletter, website,offer as free bonus or part of a product for sale as longas no changes a Gone are those times when the companies and the organisations didn't need a hi-tech system to handle them. Owing to the considerable increase in the business sector and thus, an enormous increase in the complexity of the organisational struc

----------------------------------------------------------Permission is granted for the below article to forward,reprint, distribute, use for ezine, newsletter, website,offer as free bonus or part of a product for sale as longas no changes are made and the byline, copyright, and theresource box below is included. ----------------------------------------------------------Plug and Play Resource AllocationBy Stephen BucaroYour computer has many devices connected to it. Your keyboard is a device. Your mouse is a device. Your modem isa device. Even a port, like a USB port, is a device. Youcan add a device to your computer by installing it into anexpansion connector on the the motherboard of the computer.In order to operate, resources need to be allocated to thedevice.One of the most important resources a device needs is anInterrupt Request (IRQ) line. An IRQ signals the processorthat the device needs attention. For example, each timeyou press a key on your keyboard, an IRQ is sent to letthe processor know that the keyboard needs attention. Adevice also needs to be allocated a set of memory addresseswhere commands can be sent to it and it can send responses.Many devices need to be allocated an area of memory tostore data and/or a Direct Memory Access (DMA) channel.A DMA channel allows a device to create a data streamdirectly between it and the computers memory withoutpassing through the processor.One of the most important structures in a computer is thesystem bus located on the motherbord. The processor,chipset, memory, and expansion slot devices communicateover the bus. Early PCs used a bus called Industry StandardArchitecture (ISA). When you installed an expansion cardinto the ISA bus, you had to set IRQs and other resourceswith jumpers and/or DIP switches on the card. ISA devicescannot share resources, each ISA device must have its ownIRQ.- You can have more than one ISA device configured for thesame IRQ, as long as only one of the device drivers isloaded at any one time; otherwise, you'll get an IRQconflict.Since a computer has only a limited amount of resources,the number of devices that a computer could support islimited. One of the most limited resources is IRQ lines.A PC has only 16 IRQs. Common devices such as the keyboard,mouse, floppy drive, and hard drive use a standard set ofresources.Standard IRQ aassignmentsIRQDevice0System Timer1Keyboard2IRQ Controller 23COM24COM15LPT26Floppy Drive7LPT18Real-Time Clock9ACPI10unallocated11IRQ Holder12Mouse13Math Coprocessor14Primary IDE15Secondary IDEIn 1993, Microsoft and Intel developed Plug and Play (PnP)to solve this problem. One of the main structuressupporting PnP is the Peripheral Component Interconnect(PCI) bus. Along with a PCI bus, the computers BIOS,operating system, and hardware devices must be PnPcompliant. One of the key features of PnP is that wheninstalling a PCI card, you do not need to use jumpers ofDIP switches to set the IRQ or I/O address for the card,the PCI bus controller does this for you.The Windows 2000/XP operating system component responsiblefor PnP is the Advanced Configuration and Power Interface(ACPI). ACPI allows devices to be controlled by theoperating system to perform power management. ACPI may puta device in a power saving state such as Standby, Suspendor Off. ACPI also allows dynamic handling of events likethe addition or removal of a USB device.During the boot process, the BIOS builds a table to recordwhich IRQs have been used by legacy ISA devices and thenassigns the unused ones to the PCI bus controller. The PCIbus controller, which is part of the motherboard chip set,manages the PCI bus and the expansion slots.Each PCI device communicates its resource requirements toACPI. Based on the resource requests that each device makes,ACPI assigns resources such as IRQs, I/O addresses, andmemory locations, and DMA channels. ACPI can reconfigureresource assignments when needed, for example, when adevice is added to the system. The PCI bus overcomes the limitation in available IRQ'swith a feature called "PCI steering". PCI steering makesit possible for several devices to use the same IRQ. PCIsteering allocates an IRQ called the "IRQ Holder" for PCIsteering. The PCI controller steers that IRQ to its owninterrupt systems on the PCI bus. These interrupts arecalled A, B, C, D, and so on to avoid confusion with thenumbered system IRQs. One interrupt is assigned to eachPCI expansion slot.To see which IRQ has been assigned to the IRQ Holder forPCI steering, open the Control Panel "System" utility. Inthe "System Properties" dialog box, select the "Hardware"tab and click on the "Device Manager..." button. In DeviceManager's "View" menu select "Resources by type", thenopen the "Interrupt request IRQ" branch.pcirq.bmp- Note that Windows 2000 uses IRQ 9 for PCI Steering, sonever set a device to IRQ 9.PnP resource allocation removes the need to use jumpers ofDIP switches to set the IRQ and other resources for devices.But PnP involves a complex interaction between the computersBIOS, chipset, PCI bus, operating system, and PnP devices.----------------------------------------------------------Resource Box:Copyright(C)2004 Bucaro TecHelp. To learn how to maintainyour computer and use it more effectively to design a Website and make money on the Web visit bucarotechelp.comTo subscribe to Bucaro TecHelp Newsletter visithttp://bucarotechelp.com/search/000800.asp---------------------------------------------------------- Article Tags: Play Resource, Resource Allocation