There are different types of registry keys and settings. They are usually stored as binary, decimal, and hexadecimal numbers.
• REG_BINARY Raw binary data for storing hardware component information.
• REG_DWORD Data represented by a 4-byte number (32-bit integer). DWORDS are used as the parameters for many settings, including device drivers and software and configuration options.
• REG_EXPAND_SZ A variable length data string.
• REG_MULTI_SZ A multiple string, for example a list of multiple values in a format that people can read. These are usually separated by commas or spaces.
• REG_SZ A fixed-length text string.
• REG_RESOURCE_LIST A resource list in a series of nested arrays. These are used by device drivers.
• REG_RESOURCE_REQUIREMENTS_LIST An array list of hardware resources required by device drivers.
• REG_FULL_RESOURCE_DESCRIPTOR Nested arrays used to store resource lists for physical hardware devices.
• REG_NONE Data without any particular type.
• REG_LINK A Unicode string that names a symbolic link.
• REG_QWORD Data that is represented by a 64-bit integer.
In the same way that 64-bit versions of Windows 7 have two Program Files folders for 32-bit and 64-bit programs, the registry contains different sections for 64-bit registry keys. You can find these in HKEY_LOCAL_MACHINE\Software\WOW6432Node.
Source of Information : Microsoft Press - Troubleshooting Windows 7 Inside Out