Section 4.3. Value Types


4.3. Value Types

Values are where Registry data is actually stored (as opposed to keys, which are simply used to organize values). The Registry contains several types of values, each appropriate to the type of data it is intended to hold. There are six primary types of values that are displayed and modified in the Registry Editor:


String values (REG_SZ)

String values contain strings of characters, more commonly known as text. Most values discussed in this book are string values; they're the easiest to edit and are usually in plain English. In addition to standard strings, there are two far less common string variants, used for special purposes:


Multistring values (REG_MULTI_SZ)

Contain several strings (usually representing a list of some sort), concatenated (glued) together and separated by null characters (ASCII code 00). The dialog used to modify these values is the same as for binary values. Note that the individual characters in REG_MULTI_SZ keys are also separated by null characters, so you'll actually see three null characters in a row between multiple strings.


Expandable string values (REG_EXPAND_SZ)

Contain special variables into which Windows substitutes information before delivering to the owning application. For example, an expanded string value intended to point to a sound file may contain %SystemRoot%\media\startup.wav. When Windows reads this value from the Registry, it substitutes the full Windows path for the variable, %SystemRoot%; the resulting data then becomes (depending on where Windows is installed) c:\windows\media\startup.wav. This way, the value data is correct regardless of the location of the Windows folder.


Binary values (REG_BINARY)

Similarly to string values, binary values hold strings of characters. The difference is the way the data is entered. Instead of a standard text box, binary data is entered with hexadecimal codes in an interface commonly known as a hex editor. Each individual character is specified by a two-digit number in base 16 (e.g., 6E is 110 in base 10), which allows characters not found on the keyboard to be entered. Note that you can type hex codes on the left or normal ASCII characters on the right, depending on where you click with the mouse.

Note that hex values stored in binary Registry values are displayed in a somewhat unconventional format, in which the lowest-order digits appear first, followed by the next-higher pair of digits, and so on. In other words, the digits in a binary value are paired and their order reversed: the hex value 1B3 thus needs to be entered as B3 01. If you want to convert a binary value shown in the Registry Editor to decimal, you'll have to reverse this notation. For example, to find the decimal equivalent of 47 00 65 6e, set the Windows Calculator to hexadecimal mode and enter 6e650047, and then switch to decimal mode to display the decimal equivalent, 1,852,112,967.

Binary values are often not represented by plain English and, therefore, should be left unchanged unless you either understand the contents or are instructed to change them by a solution in this book.


DWORD values (REG_DWORD)

Essentially, a DWORD is a number. Often, the contents of a DWORD value are easily understood, such as 0 for no and 1 for yes, or 60 for the number of seconds in some timeout setting. A DWORD value is used only where numerical digits are allowed; string and binary types allow anything.


Warning: In some circumstances, the particular number entered into a DWORD value is actually made up of several components, called bytes. The REG_DWORD_BIGENDIAN type is a variant of the DWORD type, where the bytes are in a different order. Unless you're a programmer, you'll want to stay away from these types of DWORD values.

The DWORD format, like the binary type, is a hexadecimal number, but this time in a more conventional representation. The leading 0x is a standard programmer's notation for a hex value, and the number is properly read from left to right. The equivalent decimal value is shown in parentheses following the hex value. What's more, when you edit a DWORD value, the edit dialog box gives you a choice of entering the new value in decimal or hex notation.

Even if you're not a programmer, you can figure out hexadecimal values pretty easily with the Windows Calculator (calc.exe). Just enter the number you want to convert and click the Hex radio button to see the hexadecimal equivalent; 435 decimal is equal to 1B3 hex.


Tip: If you aren't sure about the meaning of a specific Registry value, don't be afraid to experiment. Experimenting might include editing a value with the Registry Editor, but it might be easier or safer to work from the other end: open the application whose data is stored there (e.g., a Control Panel applet), change a setting, and watch how the Registry data changes. In this way, you can derive the meaning of many binary-encoded values. Note that although the Registry data will often change immediately, you may need to press F5 (Refresh) to force the Registry Editor to display the newly affected data. It's a good idea, though, to make a backup copy of a Registry key before making any changes.

QWORD values (REG_QWORD)

This is much like a DWORD value, with one difference: it is a 64-bit value, rather than a 32-bit value like DWORD.



Windows Vista Pocket Reference
Windows Vista Pocket Reference: A Compact Guide to Windows Vista (Pocket Guides)
ISBN: 0596528086
EAN: 2147483647
Year: N/A
Pages: 63

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