Some of the main topics in this chapter are
Windows NT is a wonderfully modular operating system that allows you to configure what services and devices are available at any one time. With this functionality, you also run the risk of building a house of cards. If one service or device fails, any other dependent service also will fail. This chapter helps you learn about these devices and services that in many cases run behind the scenes.
A system service is a portion of the operating system required for certain functions to occur. For example, the Spooler service allows print jobs to be accepted from an application and passed on to the printer when the printer is ready. Without the Spooler service, your computer would hold up your application while it was printing.
System services build upon the base operating system, currently installed hardware devices, and other system services. Figure 24.1 shows how system services can fit within the Windows NT operating system environment.
System services build upon the base operating system and even other services to provide new functionality.
System services also provide network connectivity, error detection, security, and other basic operating system functions. Table 25.1 shows the default system services and their functions within Windows NT.
| System Service | Description |
| Alerter | Provides notification to selected users or computers when administrative alerts such as service failures occur. The Alerter service is used by the Server service and requires the Messenger service to operate. |
| ClipBook Server | Allows remote Clipbook Viewers on other computers to see pages stored in the local Clipbook. |
| Computer Browser | Keeps track of other computers on the network and provides the information to applications when needed. Explorer and Network Neighborhood use the Computer Browser service. |
| Directory Replicator | Replicates directories, and the files in those directories, between computers on a network. This is typically used when administrators set up fault tolerant environments locally or when a local copy of a remote server would increase the performance of accessing files. |
| Event Log | Stores application, security, and system events in the event logs. The Event Log viewer allows you to see events stored by the Event Log service. |
| Messenger | Sends and receives messages sent by administrators or by the Alerter service. |
| Net Logon | Maintains the security features such as user logons and domain security. The Net Logon service also provides the mechanism by which security files are synchronized between servers within a domain. |
| Network DDE | Provides a network transport for DDE (dynamic data exchange) conversations and provides security for the DDE conversations. Applications such as Word and Excel use the Network DDE service when sharing information through DDE across a network. |
| Network DDE DSDM | The DDE Share Database Manager (DSDM) handles the management of multiple DDE conversations. It is used by the Network DDE service. |
| NT LM Security | Provides Windows NT security for RPC applications that use transports |
| Support Provider | other than LAN Manager named pipes. This service is used mainly by older database server applications. |
| Plug and Play | The Plug and Play service manages the interface between Windows NT and any Plug and Play hardware you have installed in your system. Your system must also have Plug and Play BIOS support to use this technology. |
| Remote Procedure | The RPC Locator service handles the directory of distributed applications |
| Call (RPC) Locator | such as database servers. An RPC application will use the RPC Locator to register its availability. The RPC Locator is also used by the clients to find distributed RPC server applications that are compatible. |
| Remote Procedure Call (RPC) Service | The RPC Service provides the communication function for the RPC Locator and other RPC services. |
| Schedule | The at command uses the Schedule service to run applications at specified times and dates. |
| Server | The Server service manages file and print services for users connected to the local computer. It also manages Named Pipe sharing and RPC support functions. When the Server service fails, the computer cannot be accessed from users on the network. |
| Spooler | Provides print job spooling services. When a print job is sent to a printer, the Spooler service queues it up behind any earlier print jobs waiting to be sent to the printer. When the print job is ready for printing, the Spooler service manages the flow of data from the print queue to the printer. |
| UPS | The UPS service manages the functions of an uninterruptible power supply connected to the computer and handles communication between the UPS hardware and the UPS controller service on the computer. When the power goes out, the UPS service sends a message to the UPS controller service, which manages the timing of the outage and handles any system shutdown functions. |
| Workstation | The Workstation service manages network connections, drive letter mappings, printer connections, and other local application interactions with the network. Explorer uses the Workstation service. |
Without system services, your computer would lack much of its functionality, especially considering the network functions that many of the system services handle.
In addition to the default system services, many other services can be loaded and unloaded to provide various functions within the Windows NT operating system. For instance, you can purchase software for performing backups at scheduled intervals, which is run as a system service. When you install the backup software, the system service for the scheduling function might be automatically installed into your system services list. You can even download a shareware application off the Internet that provides Telnet Server services. This system service might be automatically installed, or you might have to install the service manually. The next section describes the installation and removal process for system services.
Most software packages that contain a system service module will automatically install the service within Windows NT. However, there might be times when the system service needs to be manually installed or removed when you have discontinued use of the product.
In these cases, you need to understand how to install and remove the system services from your Windows NT configuration. A system service registers itself as "available" when it's installed and is ready to be started at any time. This installation and registration process is handled by the system service being installed. Typically, the service has commands to accomplish the following tasks:
The system services that are manually installed almost always have some sort of documentation that explains the exact syntax of the command necessary to accomplish one of these tasks. For example, if you had a system service that provided an electronic mail post office that was called POSTMAN.EXE, you might have to manually install the service, as shown by the command in Figure 24.2.
The example POSTMAN e-mail service is manually installed with the -install command line parameter.
This manual installation is usually due to a lackluster or even nonexistent installation program for the service. However, it is possible that the system service is installed manually for debugging or other reasons. More frequently, the removal command is used to eliminate an older service application or one that is no longer being used. A remove command looks similar to the installation command shown earlier.
Starting and stopping the service can also be performed through the command line; however, you might want to use the Control Panel applet named Services, which manages the startup and shutdown functions for all system services (as explained in the next section).
The Services dialog box, shown in Figure 24.3 enables you to start, stop, pause, and control the automatic startup of system services. Additionally, you can see the status of all services installed on your system through the Services applet.
The Services dialog box manages the system services installed on your computer.
System services might or might not be in use at all times. Typically, you install a service to provide some desired functionality. Because you want that functionality, that service has to be running. However, there might be times when you know that the service is not going to be used. You can shut off the service, yet keep it available for use later when conditions change.
NOTE: You must be logged on to Windows NT as a user who is part of the Administrators group to manage the startup of system services.
You might need to stop a system service due to a hardware failure or for security purposes. If you're running Windows NT on your portable computer that is not attached to the network, you might want to disable the FTP service because no one can access your computer over the network. To disable a service like the FTP service, follow these steps:
2. Click Stop. Services displays a dialog box like the one shown in Figure 24.4, which lets you know that it's trying to shut down the service.
The Service Control dialog box initiates the shutdown of a service when you click Stop.
After the service has been successfully stopped, the status within the Services list box is blank for that service, as shown in Figure 24.5 where the FTP service is no longer running.
After the FTP service has been stopped, the status within the Services dialog box changes to a blank.
There might be times, though, when stopping the service is too abrupt. For example, you might be using your Windows NT system on the network with users accessing the FTP service. Instead of stopping the service, which cuts off all the users currently transferring files, you could pause the service, which lets current users finish up what they're doing but prevents new users from attaching. As soon as the current users log off your FTP service, they are unable to get back on until you continue the service. To pause the FTP service, you select the FTP service from the Services Control Panel applet list box and then click Pause. This prevents new users from logging on to your FTP service. Figure 25.6 shows the FTP service in the paused state.
The FTP service is paused, only enabling current users to continue their transactions.
To resume a paused service, select the FTP service from the Services list box and click Continue. This restarts the FTP service and allows new users to access your system.
Sometimes the process of starting and stopping a service needs to be automated. You might not want to have to start the FTP service manually each time you start your computer. To instruct Windows NT to automatically start a service when it boots, follow these steps:
2. Click the Startup button to reach the dialog box shown in Figure 24.7.
The Service startup dialog box enables you to manage the initialization of a system service during boot time.
4. If you want to have the service logged on with limited rights to the system, you can choose a user ID and password that you've set up with the appropriate rights. If you have not set up a particular account for a service, then choose the System Account option from the Log On As section.
CAUTION:
Make sure that you know what your system service is doing when you load it on your system. If you assign System Account privileges to a service that has been written by a hacker, you can cause great damage to your system. Most system services will provide only the functionality that they say, but like viruses, not every application is a friendly one.
NOTE: Most services assume that they'll be logged on as the System Account and have access to all resources. If you decide to manage your services by using user accounts with specific permissions, make sure that you consult the software vendor to see what the service needs to access.
The Manual and Disabled startup options provide you with additional flexibility over how a service is initialized. For example, if your Windows NT system was providing FTP services only occasionally, you might want to set this startup option to Manual. This will prevent access to your system via FTP when you don't want it and will save memory by not running a service that you don't need.
The Disabled function prevents you or another service from accidentally starting the service. For example, you might want to disable a network backup agent if you don't want your system automatically backed up while it is connected to the network. If a backup scheduler service tried to start the network backup agent service, it would return a message indicating that the service has been disabled rather than automatically starting the backup agent.
System devices require far less attention than system services after they are installed. Because hardware changes far less frequently than software on your computer, these system devices can be installed and go unnoticed for years.
However, to ensure that your system is running at peak efficiency when you install Windows NT, you should verify that the correct system devices have been installed on your system. This section covers the details that you need to verify when managing system devices within Windows NT.
System devices, like system services are operating system modules that provide functionality. However, system devices are communication modules or drivers that are linked very closely to the hardware to which the system device driver is communicating. For example, your mouse uses a system device driver to communicate between the mouse hardware and the operating system. The mouse system device driver takes hardware signals and provides operating system events. When you move the mouse, the hardware relays signals back to the device driver, which interprets them and passes on an operating system event. Windows NT then uses that event to position the mouse cursor on the screen based on the data received by the mouse system device driver. Figure 24.8 depicts the interaction between the mouse hardware and Windows NT.
The mouse system device driver handles the interpretation of hardware signals into operating system events.
Generally speaking, the system device driver is one of the lowest-level software components within the operating system. Figure 24.9 shows how the system device fits in with the Hardware Abstraction Layer (HAL) and system services.
The system device builds a platform on top of the hardware so that the Windows NT Hardware Abstraction Layer can manage the system services without knowing about the details of the hardware.
System devices include the following types of drivers:
Because system devices are so critical to the operation of your computer within Windows NT, take a look at how you can install or remove system devices safely.
Most hardware is configured by using one of Control Panel's device managers. For example, to modify your computer's video display, you would most likely use the Display applet from within Control Panel rather than the Devices applet. Although you can modify the video system device driver through the Devices applet, the Display applet provides a more intuitive and automated way to make the change. Additionally, the Display applet will allow you to test the various options available for the video display system device.
NOTE: PCMCIA devices, also known as PC Card devices, use the PC Card (PCMCIA) device driver to manage the drivers used for each specific card you install. The first time you install a PC Card in your system, you need to open the PC Card (PCMCIA) applet to install the specific driver for that PC Card.
Table 24.2 outlines the various hardware components and the proper installation or management tool within Windows NT. Use these methods of managing the respective system devices before you attempt to make any changes within the Devices applet in Control Panel.
| System Hardware | Proper Management Tool |
| Video display | Display applet |
| SCSI Adapter | SCSI Adapters applet |
| Multimedia/Sound Board | Multimedia applet |
| PCMCIA Devices | PC Card (PCMCIA) applet |
| Network Interface Cards | Network applet |
| CD-ROM drives | SCSI Adapters applet |
| NTFS/FAT File Systems | Drive Manager application within the Administrative Tools Start menu folder. |
| Disk/IDE drives | Devices applet |
Although the management tools vary for the different types of system devices, you can still manage all system devices from within the Devices applet in Control Panel. Figure 25.10 shows the Devices dialog box containing the list of the system device drivers that are either installed or available for installation off the Windows NT CD.
All system devices can be managed from within the Devices applet in Control Panel.
Within the list box in the Devices dialog box, you can see the current status of a particular driver. A system device driver is typically installed and running at all times; however, you can encounter the situation when a system device driver is not running due to hardware failure or incorrect I/O or memory settings.
For example, assume that you've purchased a new 6X speed IDE CD-ROM drive to replace your older 2X speed Mitsumi CD-ROM. You'll have to both add the new CD-ROM device driver and remove the old one using the SCSI Adapters applet in Control Panel. Figure 24.11 shows the SCSI Adapter applet.
The SCSI Adapters applet can be used to install new SCSI Adapter device drivers or drivers for other storage device interface hardware such as proprietary CD-ROM interfaces or disk arrays.
To add a new CD-ROM device driver:
2. Open Control Panel and run the SCSI Adapters applet.
3. Select the Drivers property sheet and click Add.
4. Select the appropriate driver from the list of known drivers or insert the floppy disk that contains the Windows NT device driver supplied by the manufacturer and click Have Disk.
5. Click OK. Windows NT now asks you where to find the device driver that matches the device you are trying to install. Choose the disk drive that contains the system device driver you copied in Step 1.
TIP: You can be caught in a bind when installing a CD-ROM device because you won't have the Windows NT CD-ROM from which to copy the appropriate drivers. If you have enough additional hard drive space (about 100 megabytes), you might want to copy the entire /I386 (or whatever processor you are running) directory to your local hard drive. Because device driver names might not make any sense (SPARROW.SYS = Adaptec SCSI Device Driver), you might not know exactly which driver to copy in Step 1. With the entire Windows NT installation on the local hard drive, you won't need to know the file name of the driver.
Removing a system device is much easier than installing one. For example, if you were removing the Mitsumi CD-ROM device driver, you would:
2. Select the appropriate device driver from the list.
3. Click Remove and confirm that you want to remove the device driver; then reboot Windows NT for the changes to take effect.
If you don't know which device driver to remove from your computer, check the System Event Log, which contains details about device failures. Figure 24.12 shows the System Event Log depicting the failure of the Mitsumi system device.
The Devices dialog box enables you to manage not only which device drivers are loaded on your system but also when they are loaded during the boot process. For example, most storage management hardware such as disk drives, IDE hard drives, and CD-ROM drives will be loaded as the operating system boots. To manage when a system device driver is loaded:
2. Select the system device driver that you want to manage.
3. Click Startup. This displays the dialog box shown in Figure 24.13.
4. You can select any of the options shown in Figure 24.14, but you should have instructions from your manufacturer that will let you know the proper selection. Don't change these options unless you've been given instructions by the vendor!
The System Event Log is a good place to check for the name of the system device driver that has failed when you remove a piece of hardware.
The Device startup dialog box lets you control when a system device driver is loaded.
CAUTION: Although you can make changes to the system device drivers in this way, it's suggested that you get explicit instructions from your hardware vendor before altering the operation of any system device driver.
If you want to verify a system device driver's settings, you can load the Windows NT Diagnostic Tool. This is helpful when you have installed the correct system device driver, yet Windows NT generates an error when you attempt to load the device. Figure 24.14 depicts the Windows NT Diagnostic Tool dialog box showing the system devices loaded on the computer.
The Windows NT Diagnostic Tool is helpful when troubleshooting system device driver installation problems.
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