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On Windows 9x computers, an older installation can have a very large registry that slows down the computer's startup and can make the computer unstable. This has led to frequent criticisms that the registry leads to instability. However, these problems do not usually occur on the Windows NT family of systems, including Windows XP
The Registry is split into a number of logical sections. These are generally known by the names of the definitions used to access them in the Windows API, which all begin "HKEY" (an abbreviation for "Handle to a Key"), and are often abbreviated to a 4 letter short name.

HKEY_CLASSES_ROOT (HKCR) stores information about registered applications, including associations from file extensions and OLE object class ids to the applications used to handle these items.
HKEY_CURRENT_USER (HKCU) stores settings that are specific to the currently logged in user.
HKEY_LOCAL_MACHINE (HKLM) stores settings that are general for all users on the computer.
HKEY_USERS contains subkeys corresponding to the HKEY_CURRENT_USER keys for each user registered on the machine.
HKEY_CURRENT_CONFIG contains information gathered at runtime; information stored in this key is not permanently stored on disk, but rather regenerated at boot time.
(Note that on Windows XP, all keys other than HKEY_USERS and HKLM are mirrors of other keys. For example, HKCR is a compilation of HKCU\Classes and HKLM\Classes, and HKCU mirrors the current user's subkey of HKEY_USERS.)

Each of these keys is divided into subkeys, which may contain further subkeys, and so on. Any key may contain values, which are either strings, "DWords" (numbers between 0 and roughly 4 thousand million), lists of strings, or binary data. Each key has a default value, which is in effect a value with the same name as the key. Registry keys and values are specified with a syntax similar to Windows' filenames, using backslashes to indicate levels of hierarchy. E.g. HKLM\Software\Microsoft\Windows refers to the subkey "Windows" of the subkey "Microsoft" of the subkey "Software" of the HKEY_LOCAL_MACHINE key.

The HKLM and HKCU nodes have a similar structure to each other; applications typically look up their settings by first checking for them in "HKCU\Software\Vendor's name\Application's name\Version\Setting name", and if the setting is not found looking instead in the same location under the HKLM key. When writing settings back, the reverse approach is used -- HKLM is written first, but if that cannot be written to (which is usually the case if the logged in user is not an administrator), the setting is stored in HKCU instead
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A software development kit (SDK) is available for Windows, which provides documentation and tools to enable developers to create software using the Windows API and associated Windows technologies.
The Windows API has always exposed a large part of the underlying structure of the various Windows systems for which it has been built to the programmer. This has had the advantage of giving Windows programmers a great deal of flexibility and power over their applications. However, it also has given Windows applications a great deal of responsibility in handling various low-level, sometimes tedious, operations that are associated with a Graphical user interface.

Charles Petzold, writer of various well read Windows API books, has said: "The original hello-world program in the Windows 1.0 SDK was a bit of a scandal. HELLO.C was about 150 lines long, and the HELLO.RC resource script had another 20 or so more lines. (...) Veteran C programmers often curled up in horror or laughter when encountering the Windows hello-world program."[9]. A hello world program is a frequently used programming example, usually designed to show the easiest possible application on a system that can actually do something (i.e. print a line that says "Hello World").

Over the years, various changes and additions were made to the Windows Operating System, and the Windows API changed and grew to reflect this. The Windows API for Windows 1.0 supported fewer then 450 function calls, where in modern versions of the Windows API there are thousands. However, in general, the interface remained fairly consistent, and an old Windows 1.0 application will still look familiar to a programmer who is used to the modern Windows API.[10]

A large emphasis has been put by Microsoft on maintaining software backwards compatibility. To achieve this, Microsoft sometime even went as far as supporting software that was using the API in a undocumented or even (programmatically) illegal way. Raymond Chen, a Microsoft developer who works on the Windows API, has said that he "could probably write for months solely about bad things apps do and what we had to do to get them to work again (often in spite of themselves). Which is why I get particularly furious when people accuse Microsoft of maliciously breaking applications during OS upgrades. If any application failed to run on Windows 95, I took it as a personal failure
]]> Gg http://www.desoft.co.uk/index.php?itemid=5 Wed, 2 Nov 2005 05:50:49 -0500 http://www.desoft.co.uk/index.php?itemid=4 Ff http://www.desoft.co.uk/index.php?itemid=4 Fri, 15 Jul 2005 05:47:29 -0400 http://www.desoft.co.uk/index.php?itemid=3 Ff http://www.desoft.co.uk/index.php?itemid=3 Fri, 15 Jul 2005 05:46:43 -0400 http://www.desoft.co.uk/index.php?itemid=2 Dd http://www.desoft.co.uk/index.php?itemid=2 Fri, 15 Jul 2005 05:45:10 -0400