阿元包文件通常被歸類為一個壓縮文件,而這些元數據包文件都集成了壓縮規範專有的蘋果,特別是適用於Mac OS X平台開發了Macintosh的安裝程序包的小程序。這些元數據包文件也執行與編碼標準,再次專有的蘋果,用來存儲在MPKG格式文件的生成。自解壓的功能也被內置到這些元包文件,以便用戶只需要執行的MPKG文件,並允許存儲在MPKG文件的源代碼中提取某些文件和文件夾,並將它們存儲在Mac OS X系統的指定目錄。這些元數據包文件的內容通常是源代碼還是由蘋果公司安裝的Macintosh安裝程序包為Mac OS X的這些可能包括操作系統更新,小升級和修復或補丁開發的算法。在Mac OS X平台,在這些元數據包文件的執行和初始化,引用存儲在MPKG文件中的數據和定位包含在Macintosh上安裝程序包中的其他程序文件,所以Mac OS X可以存儲在特定的文件和文件夾相應的目錄和執行其他相關文件,繼續與Macintosh安裝程序包的安裝。
Apple Installer is a system software installer which is already integrated in OS X, or the operating system of Macintosh computers. It has the function to install and extra files of .pkg packages. This installer was first created by NeXT but later maintained and republished by Apple Inc., yet the purpose is still to help developers and creators of software in creating installers for different applications and programs. The versions released by Apple are System 6, System 7.5, Mac OS 7.6, and Mac OS X with distinctive features each. Installer System 6 was a dialogue box so a user could not switch back to the Finder; however, there is a selection of items via the Custom Install. Installer 7.5 was a separate window with windows that are resizable, title bars, info buttons, and hierarchical triangular list view. Installer (Mac OS 7.6) is presently called as the umbrella installer with routine that must be executed. Lastly, the Mac OS X is the centralized program for Mac OS X computers that includes Installer application and to-be-installed software as a package.