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What is a system library

DLL - dynamic system library

In general terms, the library system is a data warehouse, the operating system or application software in the course of work or compilation.


System libraries often containfound subroutines and functions. With regard to programming, the libraries are stored common classes for working with graphics, arrays, and other dialogs.
The concept of a library system is applicable to both individual programs and to the operating system as a whole, and this applies to the Windows and families, and the UNIX, and Mac.

The term "library" first appeared in 1951 in the book M. Wilkes, D. Wheeler and S. Gill "Drawing programs for electronic machines countable"

The operating principle of the system libraries are divided into dynamic and static.

Dynamic libraries

Dynamic link libraries - iscomponent that is loaded into memory at the request of a running program. Thus there is no need to copy the code routines in every application - the most common functions are stored in a library.
Also loaded into memoryLibrary can be used by multiple applications simultaneously, which saves system resources. This was especially true in the early days of computing.
Files shared libraries in OC Windows haveextension .dll (Dynamic Link Library) and stored in the directory system32. Similar components are shared objects (shared objects) are called UNIX-like systems and have the extension .so, in Mac OS - .dlyb.

Maurice Wilkes and colleagues gave the following definition of the library - a short, pre-prepared program for the individual, common (standard) computing operations.

All the advantages of a modular approach to implementation ofIt failed to get the program. This is because of a phenomenon known as DLL hell, where the program asks at the same time different versions of the same library (DLL). This leads to failures and reduced operating reliability.
In the current Windows operating systems, in order to avoid conflicts, allowed the use of different versions of libraries, which increases reliability, but is contrary to the principle of modularity.

Static library

Static libraries also store a codesubroutines and functions, but in contrast to the dynamic, they are used when compiling programs. That is, the necessary code is included in the whole program. The app becomes an autonomous, independent dynamic libraries, but increases in size.
Usually in Windows these library files have the extension .lib, in UNIX-like systems - .a.
Work with most compiled languages, eg, C, C ++, Pascal, is impossible without the static libraries.

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