Windows Management and Maintenance : The Windows 7 Control Panel (part 5) - AutoPlay

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7. Device Manager

The Device Manager is so important in keeping your system working properly that it can be accessed from two different categories: System and Security and Hardware and Sound. When the Device Manager is launched, you are presented with a category list of the devices installed in the system (see Figure 7). When there are no problems, the display is a bit bland (but in this case, bland is good). To see the individual devices, expand any of the listed categories. Then, to access a device’s Properties dialog box, just double-click it.

Figure 7. The Device Manager displaying an unknown device.

The Device Manager serves several functions, the foremost of which is to aid in the resolution of hardware problems. When any device fails to function as expected, it will be highlighted with a yellow triangle or a down arrow. The yellow triangle indicates a warning or a possible problem, such as a driver that has not been loaded or an Unknown Device (see Figure 7). A down arrow indicates a disabled device, device conflict, or other serious error. When the Device Manager is launched and a device has an outstanding issue, its category will be expanded so that you can easily see the warning or error icon.

When a device’s Properties dialog box is opened, the General tab displays basic information about the device, plus details on the device’s current status. In most cases, the status report will point out exactly what is preventing the device from functioning normally. You may correct the issue on your own, or if you need help or guidance, click the Troubleshoot button on the General tab for a wizard or further guidance. This button has various labels, according to the problem you have. For example, if you have a driver problem, the button is called Reinstall Driver. If you have a resource problem, the button is called Check for Solutions. If the device is enabled, the button is called Enable Device, and so forth.

Depending on the device, there can be many other tabs in addition to the General tab. In most cases, you’ll see a Driver tab, and almost as frequently you’ll see a Resources tab. The Driver tab offers details about the currently installed driver for this device and enables you to update, roll back, or uninstall the driver.

Device driver rollback, just as in Windows XP and Vista, removes the current driver and restores the previous driver (assuming there was one). The ability to remove the current or newly installed driver and return to the previously used driver is often a lifesaver. I can’t remember how many times I’ve had to remove a new driver and then had to go through the process of reinstalling the hardware just to get the old driver back. The Roll Back Driver button performs this operation with a simple click. No muss, no fuss.

The Resources tab specifies the system resources to which the device is assigned. These include IRQ, I/O ranges, DMA, and more. On Plug and Play (PnP) devices, you can switch the settings from automatic to either a predefined configuration set or a fully customized setting. For some PnP cards, the settings on the Resources tab are read-only. In such cases, the settings are configured by the system BIOS and by the expansion slot the card is plugged into. See your system or motherboard documentation to determine how to change BIOS settings, or to determine which IRQ is assigned to a particular slot.

The Details tab, added as a standard feature to the Device Manager in Windows XP SP2, provides access to a huge list of technical details about your device. It defaults to displaying the device description (the same one you see on the main Device Manager window), but you can also view approximately 25 arcane technical details such as the Device Instance ID, Enumerator, and so on. Some devices may list additional information. A few of the most useful ways to use this tab include

  • Use the Hardware IDs and Compatible IDs selection to determine the PnP information used to install the device.

  • Use the Manufacturer selection to determine the manufacturer of the device.

  • Use the Power Capabilities selection to determine the device’s support for various power management states.

Access the Advanced tab found on some devices to configure special settings used by that device. The Power tab on USB root and generic hubs can help you determine whether a particular hub has enough power for a particular USB device. The Power Management tab found on some devices enables you to control whether the computer can turn off a device to save power and whether the device can wake the computer from standby.


Some devices are hidden from view in the Device Manager. Hidden devices include non-PnP devices and devices that have been physically removed from the computer but have not had their drivers uninstalled. To see hidden devices in the Device Manager list, choose View, Show Hidden Devices. A check mark should appear on the menu, indicating that hidden devices are showing. Click it again to hide them.

For any other tabs that may appear in a device’s Properties dialog box, be sure to consult the device’s user manual.

From the main Device Manager view, you can perform a few helpful actions:

  • Change views between devices by type, devices by connection, resources by type (IRQ, DMA, I/O port address, and memory), and resources by connection (USB ports, legacy ports, and so forth)

  • Force a scan for hardware changes

  • Show hidden devices


Windows 7 no longer supports the ISA bus, which has been with us in some form since the first IBM PC of 1981. So, don’t bother trying to run Windows 7 on a motherboard with ISA cards. Legacy ports such as PS/2 mouse and keyboard ports, serial ports, and parallel ports, which were originally serviced by the ISA bus, are now serviced by a separate legacy I/O controller on the motherboard or a legacy I/O controller component in the I/O controller hub or South Bridge component of the chipset.

Understanding and Resolving Hardware Conflicts

Windows, together with its Plug-and-Play technology, has grown far better at detecting and preventing hardware conflicts over the past few years. Still, system conflicts do arise, especially when you’re using legacy hardware, such as integrated serial and parallel ports.

Historically, configuration and installation problems were due to incorrect settings on ISA cards or integrated ports. If two cards or ports were configured to use the same IRQ, base I/O port address, DMA, or base memory address, a conflict would occur. Thanks to PnP support for legacy ports, PCI, PCI Express, and AGP cards, resource conflicts are almost unheard of in recent years.

Hardware uses four major resources:

  • IRQs

  • DMA

  • I/O port addresses

  • DMA channel


By default, the Device Manager displays Devices by Type. To see IRQ and other hardware resources in use in the Device Manager, click View, Resources by Type.

You can view the resources used by a particular device, and, depending upon the specific device and motherboard design, there are various ways to solve the rare conflicts that might occur.


PC architecture includes a means for a piece of hardware to quickly gain the attention of the CPU through a message called an interrupt request, or IRQ. An IRQ is sent directly from hardware to the CPU, which then services the request accordingly. A common example occurs when data comes in to your system’s modem or LAN card. The modem or LAN card triggers the predetermined IRQ, and the CPU then begins to execute the program code that is appropriate for handling that interrupt. In fact, a part of the OS called the interrupt handler is responsible for making it so.


You may see IRQs from 80 to 190 assigned to the Microsoft ACPI-Compliant System when you view IRQ assignments in the Device Manager or with System Information (MSInfo32).

Most systems suitable for use with Windows 7 feature an Advanced Programmable Interrupt Controller (APIC). APIC permits PCI, AGP, and PCI Express cards and non-legacy integrated devices (such as USB ports and SATA host adapters) to use IRQ settings above 15 (often called PCI IRQs). APIC is enabled through the system BIOS. Figure 8 shows a typical Windows 7 system with multiple devices assigned to PCI IRQs.

Figure 8. IRQ sharing enables this PC to use PCI IRQ 22 for IEEE-1394 host controllers and a Serial ATA host adapter.

As shown in Figure 8, IRQ sharing is enabled automatically by Windows 7 when the system supports it. In some cases, however, some motherboards might not permit IRQs to be shared, even by PCI devices.


If you no longer use legacy ports, disable them in the system BIOS. By disabling legacy ports, you enable the IRQs and other hardware resources used by serial, parallel, or PS/2 mouse ports to be available for PCI, PCI Express, and AGP devices, including integrated devices. On some systems, it may also be necessary to open the PnP/PCI dialog box in the system BIOS and assign the IRQs formerly used by legacy ports to be available for PnP/PCI devices.

If you find yourself short on IRQs or if you have two devices attempting to use the same IRQ and creating a conflict, try moving the PCI or PCI Express card to another slot. On some machines, each PCI slot’s PCI Interrupt (A through D) is mapped to an ISA-type IRQ (numbers up to 15). By simply moving a card to a neighboring slot, you may get your hardware working. Note that PCI, PCI Express, and AGP slots all use PCI interrupts, and that some systems assign the same PCI interrupt to two slots, or to a slot and an integrated device. See your system or motherboard manual for details.

DMA Channels

A typical PC has eight DMA channels, labeled 0 to 7 (DMA 4 is used as a cascade controller between DMA channels 0–3 and 5–7). DMA channels are used for rapidly transferring data between memory and peripherals without the help of the CPU. In current systems, DMA channels are used only by parallel ports in enhanced capabilities port (ECP) or enhanced capabilities port/enhanced parallel port (ECP/EPP) modes.

Although recent EIDE hard drives use a variation of DMA called Ultra DMA (UDMA) for fast data transfer, DMA transfers performed by PCI-based devices don’t use specific DMA channels. The only time a PCI device ever needs to use a DMA channel is if it’s emulating an ISA device that uses one, such as a PCI-based sound card emulating an ISA-based sound card.

I/O Port Assignments

In PC architecture, I/O ports are mapped into system memory and, therefore, are accessed by the CPU using memory addresses. As you might expect, each device that uses an I/O port must have a different port address, or data intended for one device will end up at another. However, if a device must use a bridge to communicate with the rest of the system, the device and the bridge might use the same I/O address range (see Figure 9).

Figure 9. Typical I/O assignments in a Windows 7 machine are numerous. Notice the scrollbar. Only about half the assignments are visible in this figure.


A common source of I/O contention occurs among video cards, SCSI devices, and network cards. However, most devices can use a choice of several I/O port address ranges to avoid conflicts.

Check out the I/O folder off the Hardware Resources node in Computer Management, as shown in Figure 9, to see a sample list of I/O addresses and assignments. As you can see, this folder contains quite a few assignments. Note that the addresses are in standard memory-mapping parlance—hexadecimal.

Memory Addresses

Similar to the I/O port address, the base memory address is the beginning memory address that some cards or motherboard hardware use to communicate with the CPU. Sometimes, this setting is called the RAM starting address (or start address).

If you open Computer Management and go to System Information, Hardware Resources, Memory, you’ll see memory addresses such as the following:

0xA0000-0xBFFFF      PCI bus

This address means the memory area between A0000 and BFFFF is assigned to the PCI bus. (The 0x indicates that it is a hexadecimal address.) PnP configuration enables the system to place devices that need memory addresses in nonconflicting areas. Sometimes, memory address references in hardware documentation omit the last zero (A000).

Solving Resource Conflicts

Although PCI, AGP, and PCI Express cards and integrated devices are designed to share IRQs, you may see a resource conflict when you attempt to install a legacy port, such as a serial (communications) or parallel (LPT) port.

When a hardware conflict is detected, it’s reported by the wizard at the end of the device installation process.

If you cannot select a nonconflicting setting with the device you’re installing, you have a few options:

  • Change the settings for the conflicting device with the Device Manager.

  • If the device you are attempting to install is an integrated legacy port, restart the system and select different settings in the BIOS setup. With a modern system, select Auto as the setting, which will enable the BIOS or Windows 7 to select a nonconflicting setting. If you must choose a particular IRQ or other hardware resource setting, make sure you don’t choose a setting used by another port or card. For example, it’s easy in most systems to choose the same IRQ and I/O port address range for both serial (communications) ports, causing a conflict. Be sure you choose different IRQs for each serial port.

  • In some cases, particularly with legacy ports, you may not be able to resolve a conflict and will need to disable the conflicting device on one of the cards with the Device Manager.


In general, be cautious about configuring resource settings manually. When you change settings manually, the settings become fixed, and Windows 7’s built-in device contention resolution is less likely to work. Also, if you install too many devices with manually configured settings, you might not be able to install new PnP devices because none will be available. In the worst-case scenario, the system might not even boot if conflicts occur with primary hardware devices, such as hard disk controllers or video cards. If you decide to use manual configuration, make sure you know what you’re doing and have the specs for the hardware in question at hand.

If you have a resource conflict, what should you do? Most drivers don’t have resources that can be reassigned. Others have an option button called Reinstall Driver that’s useful if the system thinks that would solve a nonfunctioning-device problem. Most PCI, PCI Express, and AGP cards (as well as integrated ports such as USB, FireWire, and PATA/SATA) don’t permit their resources to be reassigned because they obtain their resource settings from Windows or from the system BIOS. Some systems allocate resources depending on which slot you use for a particular card.

However, you can usually reassign resources for legacy ports like serial (COM) and parallel (LPT) ports. To reassign a resource, open the Device Manager, open the Properties dialog box for the device, and click the Resources tab. To select a different resource, uncheck the Use Automatic Settings box and choose Change Setting.

To select an alternative setting on most systems, clear the Use Automatic Settings check box; then click Change Setting to change the settings. If the system displays an error message, use the Setting Based On scroll box to try a different Basic configuration.


Notice the Setting Based On drop-down list on the Resources tab. It lists the hardware configurations in which the currently selected device is enabled. If you choose a hardware configuration other than the default, and you change any resource settings, resource conflicts may occur when you use the default hardware configuration. Resource conflicts can disable your hardware and cause your computer to malfunction or to be inoperable.

On some older systems, you might be able to click the resource shown in the Resource Settings window and change it directly.

In an attempt to prevent folks from inadvertently doing damage, the Resources tab keeps an eye on what you’re doing. If you attempt to reassign to a resource that is already in use using either method, you’ll be warned about the conflict. Keep trying configurations until the conflicting device listing is clear. Then, click OK and restart your computer if prompted.

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