Prebinding is a method for reducing the time it takes to launch executable

Executable

In computing, an executable file causes a computer "to perform indicated tasks according to encoded instructions," as opposed to a data file that must be parsed by a program to be meaningful. These instructions are traditionally machine code instructions for a physical CPU...

s in the Mach-O

Mach-O

Mach-O, short for Mach object file format, is a file format for executables, object code, shared libraries, dynamically-loaded code, and core dumps. A replacement for the a.out format, Mach-O offered more extensibility and faster access to information in the symbol table.Mach-O was once used by...

 file format

File format

A file format is a particular way that information is encoded for storage in a computer file.Since a disk drive, or indeed any computer storage, can store only bits, the computer must have some way of converting information to 0s and 1s and vice-versa. There are different kinds of formats for...

. For example, this is what Mac OS X

Mac OS X

Mac OS X is a series of Unix-based operating systems and graphical user interfaces developed, marketed, and sold by Apple Inc. Since 2002, has been included with all new Macintosh computer systems...

 is doing when in the "Optimizing" stage of installing system software or certain applications.

Prebinding looks up memory address

Memory address

A digital computer's memory, more specifically main memory, consists of many memory locations, each having a memory address, a number, analogous to a street address, at which computer programs store and retrieve, machine code or data. Most application programs do not directly read and write to...

es of symbols

Debug symbol

A debug symbol is information that expresses which programming-language constructs generated a specific piece of machine code in a given executable module. Sometimes the symbolic information is compiled together with the module's binary file, or distributed in separate file, or simply discarded...

 in libraries that the program is using before the program is launched, and stores this information ahead-of-time, so that the computer need not look up (bind) addresses on each launch.

Prebinding has changed a few times within the Mac OS X series. Before 10.2, prebinding only happened during the installation procedure (the aforementioned "Optimizing" stage). From 10.2 through 10.3 the OS checked for prebinding at launch time for applications, and the first time an application ran it would be prebound, making subsequent launches faster. This could also be manually run, which some OS-level installs did. In 10.4, only OS libraries were prebound. In 10.5 and later, Apple replaced prebinding with a dyld shared cache

Cache

In computer engineering, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere...

 mechanism which provided better OS performance.

The equivalent process on Linux is called prelink

Prelink

prelink is a free program written by Jakub Jelínek of Red Hat for POSIX-compliant operating systems, principally Linux . It is intended to speed up a system by reducing the time a program needs to begin...

.

See also

• Dynamic binding
• Library (computing)
• Linker (computing)
• Loader (computing)
  Loader (computing)
  In computing, a loader is the part of an operating system that is responsible for loading programs. It is one of the essential stages in the process of starting a program, as it places programs into memory and prepares them for execution...
  
  
• Object file
  Object file
  An object file is a file containing relocatable format machine code that is usually not directly executable. Object files are produced by an assembler, compiler, or other language translator, and used as input to the linker....
  
  
• Relocation
  Relocation (computer science)
  "Relocation is the process of assigning load addresses to various parts of [a] program and adjusting the code and data in the program to reflect the assigned addresses."...
  
  
• Static library
  Static library
  In computer science, a static library or statically-linked library is a set of routines, external functions and variables which are resolved in a caller at compile-time and copied into a target application by a compiler, linker, or binder, producing an object file and a stand-alone executable...
  
  
• Prelink
  Prelink
  prelink is a free program written by Jakub Jelínek of Red Hat for POSIX-compliant operating systems, principally Linux . It is intended to speed up a system by reducing the time a program needs to begin...
  
  
• Prefetcher
  Prefetcher
  The Prefetcher is a component of versions of Microsoft Windows starting with Windows XP. It is a component of the Memory Manager that speeds up the Windows boot process, and shortens the amount of time it takes to start up programs...