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Table Of Contents  CertiGuide to A+ (A+ 4 Real)
 9  Chapter 1: What are Operating Systems and How Do They Work?
      9  The Registry

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Registry Hives
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Registry Tools - RegEdit.EXE
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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.

Binary Value (Registry identifier: REG_BINARY)

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.

DWORD Value (Registry identifier: REG_DWORD)

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.

String Value (Registry identifier: REG_SZ)

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 user’s 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 Value (Registry Identifier: REG_EXPANDSZ)

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 Value (Registry identifier: REG_MULTISZ)

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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Registry Tools - RegEdit.EXE
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