File archiver

Archiving and compression programs (short packer, English short- Archiver. ) Summarize one or more other files to container files - so-called archive files - together or extract them from it again. They were once used often to archive the backup to magnetic tape (the file name extension. Tar derived for example from English = tape archiver, tape archiver ' from ).

Operation

In the simplest case be of a pack while the program to archive files easily consecutively hanged as a data stream, and in addition, the names, lengths ( and possibly the order) held the individual files in the index of the archive file. Mostly, however, some meta information can still be saved, such as creation dates, permissions and file attributes, such as the archive bit. These can be modified at the user may also when packing (eg resetting the archive bit after successful archiving).

Even if the archive is in the foreground, the data are usually additionally compressed to save space .. Hence the term archiving program is often used when actually a data compression program is meant. Even pure compression tools such as tar are often used in data compression to data compression programs such as gzip or bzip2, treating only individual files, multiple files to a previously summarized (progressive compression).

File application

In addition to explicit packaging programs and file managers support the Pack Programs using some application programs the same or similar built-in algorithms for their data and settings. Other decompress provided (and usually only data to be read ) during the term. For example, some programs want the free file for the assignment of IP addresses to countries GeoIP.dat.gz already unpacked in the data directory have reside, others directly use the compressed version.

In addition, there are compression programs for program files (*. Exe, *. Dll, etc.) that get the ability to run the programs, such as UPX. Depending on the system, the programs will be unpacked in memory only, or create a local temporary file. Partly it comes to save disk space, which was relevant in times of disk drives and is now particularly relevant even for small computers such as embedded systems. Otherwise it can now bring a speed advantage when the program starts of slow disks or directly over the network, where the computation time to decompress the weight falls less than the data transfer rate. In addition, the program files before disassembling simple experiments are protected. Packers who use a password protection when Dekomrimieren outside of the term or installed a kryprografische encryption to protect effectively against analysis, reverse engineering and modifications.

Program development

So-called Archiver are also used in the field of program development. There summarizes an Archiver many object files in an archive ( also called library ) together. Instead of the individual object files to the linker only has the name of the archive to be called, from which it then seeks out the necessary object files in order to integrate them into the target file.

An example of Archiverprogramme in the latter sense are the ar65 Archiver the C compiler cc65 or the packer used on Unix operating systems ar, which is now being used, among other things chiefly so.