Patches

In computing, a patch is a small piece of software designed to update or fix problems with a computer program or its supporting data. This includes fixing bugs, replacing graphics and improving the usability or performance. more...

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Though meant to fix problems, poorly designed patches can sometimes introduce new problems (see software regressions).

Patch management is the process of using a strategy and plan of what patches should be applied to which systems at a specified time.

Types

Programmers publish and apply patches in various forms. Because proprietary software authors withhold their source code, their patches are distributed as binary executables instead of source. This type of patch modifies the program executable—the program the user actually runs—either by modifying the binary file to include the fixes or by completely replacing it.

Patches can also circulate in the form of source code modifications. In these cases, the patches consist of textual differences between two source code files. These types of patches commonly come out of open source projects. In these cases, developers expect users to compile the new or changed files themselves.

Because the word "patch" carries the connotation of a small fix, large fixes may use different nomenclature. Bulky patches or patches that significantly change a program may circulate as "service packs" or as "software updates". Microsoft Windows NT and its successors (including Windows 2000, Windows XP, and later versions) use the "service pack" terminology.

In several Unix-like systems, particularly Linux, updates between releases are delivered as new software packages. These updates are in the same format as the original installation so they can be used either to update an existing package in-place (effectively patching) or be used directly for new installations.

History

Applying a patch once involved a tedious, error-fraught process that required end-users to follow an often ill-documented set of procedures. Missing or misapplying a step usually resulted in having to re-install both the application and patch. Today, patch installation generally occurs automatically.

Historically, software suppliers distributed patches on paper tape or on punched cards, expecting the recipient to cut out the indicated part of the original tape (or deck), and patch in (hence the name) the replacement segment. Later patch distributions used magnetic tape. Then, after the invention of removable disk drives, patches came from the software developer via a disk or, later, CD-ROM via mail. Today, with almost ubiquitous Internet access, end-users must download most patches from the developer's web site.

Today, computer programs can often coordinate patches to update a target program. Automation simplifies the end-users' task -- they need only to execute an update program, whereupon that program makes sure that updating the target takes place completely and correctly. Service packs for Microsoft Windows NT and its successors and for many commercial software products adopt such automated strategies.

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