Registry Keys and Values
Within these hives, data is stored in a specific format organized into keys and values. A registry key is approximately equivalent to a folder on a hard drive, in that it can contain data and sub keys. A value is a single piece of data represented by a text string, stored within a key.
There are 5 types of values.
As the name suggests, a binary value can only represent an on or off Boolean value. These values are normally used to represent single choice options in applications such as check boxes, where the option can only be checked or unchecked.
A DWORD is short for double word, a 32-bit data type used for storing numerical data. DWORDs can be split into HIWORDS and LOWORDS, depending on which 16 bits of the value are significant (in other words, used to store data in). Although hexadecimal by necessity, a DWORD can store an integer value.
A string value simply stores a text string, whether it is used internally within an application (as a license key, for example) or for the users benefit (by showing them the filename of the last file they saved). The SZ part of the Registry identifier comes from Hungarian Notation, a style of programming in which string variables are prefixed with sz.
Expansion strings are used in conjunction with environment variables. Environment variables were covered in. These values are the same as string values, but accept embedded environment variables. For example, a REG_EXPANDSZ value called System32DirectoryLocation may contain %systemroot%\system32. The %systemroot% is an environment variable set to the Windows directory location, usually C:\WinNT or C:\Windows. When an application reads this key, whilst it may contain %systemroot%\system32 in the Registry, the application will actually see it as C:\WinNT\system32.
MultiString values are storage containers for string values. As the name suggests, multiple individual strings can be stored within one multistring value. These types are rarely used, but do have one interesting property that will be covered shortly.
When referring to a registry location it is normal to use the abbreviated hive name followed by the key structure and value name delimited by obliques, in a similar style to a directory path. For example, to refer to a string value called CompTIA in a key named Exams in the HKEY_LOCAL_MACHINE hive the following convention may be used: HKLM\Exams\CompTIA.
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