HKEY_DYN_DATA
HKDD is a fake key--it doesn't really exist. It serves as a convenient
doorway to device driver, Win32 application, and native NT performance counters
via the Registry API. When a Win32 program queries a value or key in HKDD, the
request gets routed as an I/O request to the appropriate driver or Win32
program, which returns information that looks like the result of an authentic
Registry access. The Performance Monitor (Perfmon) program accesses this root
key to provide the intricate performance information it displays.
HKEY_CURRENT_CONFIG
HKCC, a new root key in NT 4.0, is a link to
HKLM\SYSTEM\CurrentControlSet\Hardware Profiles\Current, which contains the
configuration data for the hardware profile in use on the system. Microsoft
added HKCC to NT to let applications that access this key run on both Windows 95
and NT. To create, configure, and change hardware profiles, you can use Control
Panel's System, Services, and Device applets.
Registry Gems
Now that you understand the basic structure of the Registry, let's look at a
few handy settings for data stored in the Registry. As always, before you try
any of the following suggestions, back up your Registry. Editing Registry
entries incorrectly can cause systemwide problems that may require you to
reinstall NT to correct them.
Auto-logon. If you have a private NT system (e.g., a
machine you use at home), you can configure NT to automatically log you on when
you boot NT. To enable auto-logon, you must modify four values in HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon. First, set the AutoAdminLogon value to 1. Then specify appropriate strings for DefaultDomainName,
DefaultPassword, and DefaultUserName. The next time you reboot, you'll
automatically be logged on.
Tuning a workstation for server-like workloads. NT
Workstation and NT Server have vastly different performance characteristics
because of the internal tuning NT performs. You cannot access most tuning
parameters, but you can find a few in the Registry. If you run NT Server and
double-click the Server entry of the Services tab in Control Panel's Network
applet, you get a dialog box that lets you determine what type of applications
you want to tune the machine for. You can choose among Minimize Memory Used,
Balance, Maximize Throughput for File Sharing, and Maximize Throughput for
Network Applications. Systems running NT Workstation do not present this dialog
box. The options change two Registry values:
HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Memory Management\LargeSystemCache
and HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\Size.
Table 7
lists the value data you need to enter in the Registry of a system running NT
Workstation to achieve the same tuning options the NT Server dialog box offers.
Previewing bitmaps in their icons. How many times have you
wished you could get a quick look at what's in a bitmap file without opening it?
You can, with a simple Registry setting. Just change the value of
HKCR\Paint.Picture\DefaultIcon to "%1". Reboot for the change to
take effect.
After the Tour
These few tips conclude a whirlwind tour of the Registry. If you want to
learn more about the Registry, get Microsoft Windows NT Workstation Resource
Kit or Microsoft Windows NT Server Resource Kit, which include
extensive online documentation about the Registry. If your interest lies in
programming the Registry API, refer to the Win32 software development kit (SDK).