The Control Panel is the central location of the installation and configuration interfaces for nearly every device, service, and application NT hosts. These administration tools are indispensable for maintaining a functioning environment, as well as for fine-tuning a system to operate at its maximum capability. Each of the following sections describes a performance-related control or adjustment that can be made via a Control Panel applet.
System Applet: Virtual Memory
Virtual Memory is the combination of physical RAM with a swap file (a.k.a., paging file) stored on a disk drive to create a large memory space. This space is managed by the Virtual Memory Manager (VMM) from the Executive Services segment of the kernel. VMM handles the storage of 4K blocks or pages of memory (8K for Alpha) and switching pages between active physical RAM and inactive swap file storage. As discussed in Chapter 2, adding more physical RAM is often the best way to resolve a memory bottleneck. However, in some cases, altering the size and location of the paging file can improve performance, even if only temporarily.
The size of the paging file is managed via the System applet. Access the Virtual Memory dialog box (Figure 5.5) by clicking Change on the Performance tab of the System applet. This dialog box displays the current page file settings and lets you alter those settings.
The top area lists the drives that can be used to host paging files and indicates which drives are currently hosting paging files. Use the “Paging File Size for Selected Drive” area to alter or create a paging file. First, select a drive from the drive list, then define an initial size and maximum size for the paging file on that drive. Click Set and your changes are reflected in the drive list. The initial size setting is how much space the system allocates for the paging file. The initial allocated space cannot be used by any other file; it is reserved for the paging file. The maximum size is the upper limit to which the system can expand the paging file as necessary. This setting does not guarantee enough available free space on the drive because the space is not allocated for page file use only.
Tip: To minimize the risk of a growing paging file that runs out of drive space, set both the initial and maximum sizes to the same number. Remember, however, that if you do this, the system cannot expand the paging file automatically when necessay.
You can define the paging file so that it exists on a single drive only or on multiple drives. When you first install NT, a paging file of 12 MB more than the physical RAM in the system is created on the boot partition (the one where the main Winnt directory lives).
Tip: I recommend creating a paging file that is twice the size of your physical RAM; however, you should test a few different sizes for the paging file to determine what really works best on your system. If you have too small paging file, the system issues you a warning that it is running out of virtual memory.
The middle section of the dialog box is titled “Total Paging File Size for All Drives”; it lists the minimum-size paging file this system requires, the recommended size for the paging file, and the size allocated to the current paging file.
Tip: As long as the maximum size available (add all the maximum settings together for all drives; this value is not displayed) is greater than the recommended size, your settings should be adequate.
You can remove a paging file from a drive by defining a size of 0 - 0. However, NT requires a minimum paging file of 2 MB to exist somewhere on the system; this interface won’t let you set a paging file size below the minimum. If Recovery settings are enabled on the Startup/Shutdown tab (see the System Applet: Startup/Shutdown section later in this chapter), NT requires a paging file of at least 2 MB to exist on the boot partition. Otherwise, the paging file can be completely removed from the boot partition.
Tip: Moving the paging file to a completely different physical disk from the one hosting the boot partition can result in significantly improved peformance.
Separating the tasks of OS disk access from paging file activity lets each task operate independently. They no longer fight for drive access over the same task queue, disk subsystem driver, and I/O pathway. The performance benefits of moving the page file are greatest on highly active systems.
Warning: Each time you change the virtual memory settings (i.e., change the page file), you must reboot the system; don’t make changes via the Virtual Memory dialog unless you are prepared to cycle the system.
At the bottom of the Virtual Memory dialog box is a control for the maximum size of the Registry, which actually designates how much of the Registry can remain in active memory. If the Registry grows too large, it can use virtual memory that applications and processes need. The Registry Size area lists the current total size of the Registry as well as the maximum memory area the Registry can consume. The default setting is 13 MB, which is usually reasonable, especially if the Registry size is less than 15 MB.
Tip: You may want to increase the maximum size for the Registry on domain controllers that are used primarily for user authentication (i.e., that do not host applications)
System Applet: Environment
The Environment tab (Figure 5.6) of the System applet is where all the environmental variables that NT sets during bootup are defined. Most of the variables listed on this tab are defined through a Registry setting.
Warning: I highly recommend that you edit these variables only when necessary and do so through the System applet rather than through the Registry.
In most cases, you should avoid altering any of the variables listed in the System Variables area. The system, services, and applications use the System Variables to access standard drives and other files. Altering them can result in a system that operates sporadically, if at all.
Warning: Altering System Variables can result in a system that operates irregularly or fails.
The variables under the User Variables for <username> can usually be safely altered. In most cases, the only variables that appear here are the temporary path defining items, which are automatically set to the TEMP directory on the boot partition. Often, the boot partition becomes cluttered with important files and space becomes limited.
Tip: Altering the drive used to create and store temporary files can improve system performance and reduce the risk of lost data. Be sure to change both TEMP and TMP variables; I also recommend setting them to the same path.
Setting an environmental variable involves selecting the variable from the list, altering the value displayed in the Value: text field, and clicking Set. Adding new variables is as easy as keying a new name in the Variable: text field, keying its value in the Value: text field, and clicking Set. Removing a variable involves selecting the variable and clicking Delete.
Tip: While not always necessary, it is a good practice to reboot your system after altering the environmental variables.
System Applet: Startup/Shutdown
The Startup/Shutdown tab (Figure 5.7) of the System applet is used to control the system startup menu and the Recovery options.
The System Startup area contains the Startup pull-down list and the “Show list for” variable. The Startup pull-down list contains all the OS selections found in the startup menu (this data is pulled from the Boot.ini file). Selecting an OS from this list moves that selection to the top of the startup menu to be selected by default. The “Show list for” variable defines how many seconds the startup menu is displayed before automatically booting using the default operating selection.
Tip: If you always boot to the same OS, we suggest setting the value for the number of seconds for which the startup menu is displayed to 5. The startup menu appears long enough to interact and select a different OS when necessary, but not so long that it wastes time.
The Recovery options control what NT does when a STOP error occurs. A STOP error is the NT equivalent of a Windows 3.1 or Windows 95 General Protection Fault (GPF). A STOP error occurs when an application or process (Ring 3) violates the system integrity by accessing protected Ring 0 components (e.g., kernel, memory, hardware) directly. The Recovery area offers four checkbox settings to control how NT responds to a STOP error:
Write an event to the system log — This setting writes an event to the System log, which can be viewed through the Event Viewer.
Send an administrative alert — This setting broadcasts an alert to all members of the administrators group currently logged into the domain.
Write debugging information to — This setting writes a memory dump file to the boot partition.
Automatically reboot — This setting automatically reboots NT.
If any of the first three checkboxes is selected, NT requires that a 2-MB paging file remain on the boot partition.
Most administrators find creating a memory dump file essentially useless. The dump file is a direct download of the entire physical RAM contents into a file; it captures the state of the system at the moment the STOP error occurred. Only specially trained Microsoft technicians can interpret this dump file, and often all they can tell you is what application caused the failure. In addition, this setting requires that you maintain free drive space of at least the size of the physical RAM on your boot partition; if you have 128 MB or more installed, this can be difficult.
Tip: Because saving a dump file is not useful to most system administrators and requires that you maintain free drive space the size of your physical RAM, disable saving this file. Record the STOP error.
Fortunately, STOP errors are infrequent. Generally, I recommend that you select having a message recorded in the Event log and that you enable automatically rebooting — so unattended systems reboot whenever a STOP error is encountered. The only exception to this is for systems with a BIOS password that prevents rebooting without an administrator present. Any change to this tab requires a system reboot.
Devices Applet
The Devices applet (Figure 5.8) lists all the hardware devices that the current HAL knows, including all active and present devices, as well as devices that are supported but not present in the system.
The status and startup settings are also displayed. Through this applet, you can start or stop any listed device, change its startup parameters, and add/remove the device from the current hardware profile.
Starting and stopping a device can be a useful troubleshooting technique for components that are not functioning properly. This procedure does not restart the device itself; it simply reloads the driver into memory. If the device itself is malfunctioning, a system reboot may be required.
Tip: A possible performance use for the stop-and-start feature is to manually disable those devices that are required for bootup or for specific applications/services - once their use complete.
A device’s startup setting indicates how the device driver is loaded during bootup. The selections accessed by clicking Startup are
Boot — This device is started during initial bootup before other devices. This selection is typically reserved for critical devices on which the system depends to boot.
System — This device is started when the system is started, after the Boot devices are started. This selection is also typically reserved for critical devices on which the system depends to boot.
Automatic — This device is started when the system is started, after the Boot and System devices are started. This selection is used for all noncritical devices.
Manual — This device can be started independently by a user or a dependent device. It is not automatically started during bootup.
Disabled — This device is not started during bootup, and users cannot start the device. However, the system can start the device if necessary.
If you are using hardware profiles, you can use HW Profiles to enable and disable individual devices for existing hardware profiles. You can create new profiles on the Hardware Profile tab of the System applet. Select a device from the Devices applet, then click HW Profiles. A dialog box listing each known hardware profile and the status of the selected device is displayed. To alter a profile status line, select it and click Enable or Disable. Changes to a hardware profile are not realized until the next time that profile is used to boot.
Tip: Removing devices from a profile can improve performance in some cases – for example, when the device is used only during backup opertations or for specialty application functions, such as those performed by scanners, digital cameras, and writable optical drives. Typically, you achieve a noticeable performance improvement only on taxed systems or systems with little physical RAM.
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