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Hack 68 Don't Fear the Registry

The Registry is the single best tool available
for hacking XP. Here's an introduction to how
it's organized and how to use it.

If you haven't spent much
time in the Registry, you can easily be cowed by it. At first glance,
it's a maze of apparently incomprehensible settings.
In fact, though, there's a method to the madness.
The Registry is a hierarchical database of information that defines
exactly how your system works, including virtually every part of XP
and its applications. Editing the Registry database is often the best
way to hack XP. In fact, there are many changes to the operating
system that you can make in no other way.

Even if you've never used the Registry directly
before, you've changed it without realizing it.
Whenever you change a setting using the Control Panel, for example,
behind the scenes a Registry change is made that puts that new
setting into effect. The menus and dialog boxes you see in XP are
often little more than a visual front-end to the Registry.

If you want to optimize XP and master every part of it,
you'll have to use the Registry. XP contains so many
different settings and customizations that it simply
wasn't possible for Microsoft to build a graphical
interface for every conceivable possibility. And there are many times
when it's easier and you get more options when you
edit the Registry rather than using the graphical XP interface. You
can use Windows XP without ever editing the Registrymany users
dobut advanced users understand its power tool status.

The way to edit the Registry is by using the Registry
Editor , also called RegEdit,
which is shown in Figure 7-1. To run it, type
regedit at the Run box or command line and press
Enter.

Figure 7-1. Controlling Registry settings by using the Registry Editor

Before you edit the Registry, though, you should first get a basic
understanding of its structure.

Sometimes, we power users like to jump in without reading the manual. The Registry is not the best place to experiment and learn as you go, until you understand at least a little what's going on. You could render your system useless and unrecoverable with just a few changes. So, we recommend making a backup [Hack #71] and reading at least most of this chapter first. You'll be glad later if you do this now.

7.2.1 The Five Logical Registry Hives

The Registry has many thousands of
settings; in fact, it often has tens of thousands of them. They are
organized into five main Registry sections, called Registry
hives. Think of each hive as a root directory. Each of the
hives has a different purpose. When you start to delve into the
Registry, you may notice that many of the settings seem to be exact
duplicates of one anotherin other words, settings in one hive
mirror the settings in another hive. In fact, frequently one set of
settings is merely an alias (called a symbolic
link) of another, so that when you change those settings
in one place, the changes are made in both hives.

The hives themselves are stored in the C:\Windows\system32\config and C:\Documents and Settings\{username} files.

Following are the five hives and what each does:

HKEY_CLASSES_ROOT

This
hive
contains
information about file types, filename extensions, and similar
information. It instructs XP how to handle every different file type
and controls basic user interface options, such as double-clicking
and context menus. This hive also includes class definitions (hence
the word
"CLASSES" in its
name) of unique objects, such as file types or OLE objects.
Frequently, classes associated with file types contain the
Shell subkey,
which defines actions, such as opening and printing, that can be
taken with that file type.

HKEY_CURRENT_USER

This
hive
contains
configuration information about the
system setup of the user that is currently logged into XP. It
controls the current user's Desktop, as well as
XP's specific appearance and behavior for the
current user. This hive also manages

network connections and connections to
devices such as printers, personal preferences such as screen colors,
as well as security rights. Also included in this hive are

Security Identifiers (SIDs), which
uniquely identify users of the PC and which have information about
each user's rights, settings, and preferences.

HKEY_LOCAL_MACHINE

This
hive
contains information about the computer itself, as well as about the

operating system. It
includes specific details about all hardware, including keyboard,
printer ports, storagethe entire hardware setup. In addition,
it has information about security, installed software, system
startup, drivers, services, and the machine's
specific XP configuration.

HKEY_USERS

This
hive
contains information about every user profile on the system.

HKEY_CURRENT_CONFIG

This
hive
contains information about the current
hardware configuration of
the system, in the same way that HKEY_CURRENT_USER
contains information about the current user of the system.

7.2.2 Using Keys and Values

Each hive is at the top of the
hierarchy, and underneath each hive are keys, which can in turn contain
subkeys, and those subkeys can contain
subkeys, and so on, organized in folder-like fashion, much like a
hard drive.

Keys and subkeys contain a value, which
controls a particular setting. For
example, this
key:

HKEY_CURRENT_USER\Control Panel\Mouse\DoubleClickSpeed

determines the amount of time between mouse clicks that must elapse
before Windows won't consider it to be a
double-click. To set the amount of time, you change the
key's value. In this case, the default value is
500, measured in milliseconds, and you can edit
the Registry to change it to whatever value you want, as shown in
Figure 7-2. You can also make the changes using the
Mouse Properties dialog box (Start Control Panel
Printers and Other Hardware Mouse). When you
make changes to that dialog box, the changes are in turn made in the
Registry, which ultimately controls the setting. In essence, the
dialog box is merely a convenient front-end to the Registry.

Figure 7-2. Editing a Registry key's value

A key can
contain one or more values. Following are the
five primary data types of values in
the Registry:

REG_SZ (String value)

This data type is easy to understand and
edit because it is made up of plain text and numbers. It is one of
the most common data types in the Registry. The value for
DoubleClickSpeed, mentioned earlier in this hack,
is of this type.

REG_MULTI_SZ (String array value)

This data type
contains several strings of plain text and numbers. The Registry
Editor will let you edit these values, but it won't
let you create them.

REG_EXPAND_SZ (Expanded string value)

This data type contains variables
that Windows uses to point to the location of files. For example, to
point to the location of the Luna theme file, the expanded string
value in the Registry is
%SystemRoot%\resources\Themes\Luna.theme.

REG_BINARY
(Binary values)

This data type is made up of binary data: 0s and 1s. Figure 7-3 shows a typical example of a binary value. As
a general rule, you won't edit binary
valuesinstead you'll edit string values
because they're made up of text and numbers, as
shown in Figure 7-4.

Figure 7-3. Binary values

Figure 7-4. Editing String values

REG_DWORD

(DWORD values)

This data type is represented as a number. Sometimes a
0 turns on the key or 1 turns
off the key, though it can use other numbers as well.
While
you see and edit the value as a number, such as
456, the Registry itself views the number as a
hexadecimal number, 1C8.
Figure 7-5 shows a DWORD value being edited.

Figure 7-5. Editing DWORD values

7.2.3 Launching the Registry Editor

There's
an upside and a downside to using XP's

Registry Editor. The upside is that
it's relatively simple to use. The downside is that
it doesn't offer much functionality beyond basic
Registry editing.

In some instances, when you make changes using the Registry the changes take effect as soon as you exit the Registry. In other instances, they'll take effect only after you log out and then log back in. And, in yet other instances, they'll take effect only after you restart Windows.

To run the Registry Editor, type regedit in the
Run box or a command prompt and press Enter. If this is the first
time you've run the Registry Editor, it will open
highlighting the HKEY_CURRENT_USER hive, as shown
in Figure 7-6. If you've
previously used the Registry Editor, it will open highlighting the
last key you edited or the last place you were in the Registry.

Figure 7-6. Using the Registry Editor for the first time

You
can browse through the Registry with the Registry Editor in the same
way you browse through a hard disk using Windows Explorer. Clicking a
+ sign opens a key to reveal the next level down of the hierarchy.
Clicking a - sign closes the key.

The Registry can be several levels deep in keys and subkeys, so
navigating it using a mouse can take a substantial amount of time.
(Every time you open it, it jumps to the last-used key.) You can use
shortcut keys, though, to more easily navigate through the Registry.
The right arrow key opens a key to reveal subkeys; the left arrow key
closes a key and moves one level up in the key hierarchy. To jump to
the next subkey that begins with a specific letter, press that letter
on the keyboard.

You use the Registry Editor to edit
existing keys and values, create new keys and values, or delete
existing keys and values. Sometimes, the changes take effect as soon
as you make the change and exit the Registry Editor; other times,
you'll have to reboot for them to take effect. Keep
in mind that there is no "Save"
button. When you modify a value, it changes right then and there.
There is also no Undo button, so make your changes carefully.

If there's a particular key that you want to edit,
an even faster way to navigate is to use the Find command from the
Edit menu. (You can also use the Find command by pressing Ctrl-F.) To
find successive keys with the same value, press the F3 key.

To edit the data associated with a value, double-click on the value
in the right pane of the Registry Editor; a box appears that lets you
edit the value, as shown in Figure 7-7.

Figure 7-7. Editing a value

When you're editing the Registry,
it's often hard to tell what key
you're editing, because the Registry Editor
doesn't highlight that key. Instead, it shows only
an open folder icon next to it, but it's easy to
miss that icon. Check the status bar at the bottom of the Registry
Editor; it should display the key you're editing. If
it doesn't, choose View Status Bar from
the Registry Editor menu.

To rename a key, select it and
choose Edit Rename from the menu. You can also right-click
on the key and choose Edit Rename.

7.2.4 Adding and Deleting Keys and Values

Editing the Registry often requires
that you add and delete keys and values To add a new key, select the
new key's parent key in the left pane. Then, choose
Edit New Key from the menu. Type in the new
key's name. You can also right-click on the new
key's parent key and choose Edit New
Key. To delete a key, select it and press the Delete key.

Very often, you need to add values to a key in order for its changes
to take effect. To add a value to a key, select the new
key's parent key in the left pane. From the menu,
choose Edit New, and from the submenu, select the type of
value you want to create. We've already covered the
five types of values you can create; as a reminder,
they're detailed in Table 7-1.

To
create a new value, type in the name of the new value and press
Enter. Press Enter again. The Edit Value dialog box appears, as shown
in Figure 7-7. Enter your data and press
Enter.

7.2.5 See Also

For an excellent collection of Registry hacks, go to the Registry
Guide for Windows at http://www.winguides.com/registry. Make sure
to sign up for the newsletter that offers Registry advice and
hacks.