ZIP, 7z and tar.gz: What Each One Is For and What It Actually Does

ZIP as a Portable Exchange Format

ZIP is the go-to format for cross-platform file and data exchange. Zipped files package one or more files together and apply compression and sometimes encryption. The ZIP archive format, which stands for, originated with Phil Katz and has been openly documented by PKWARE since the start. APPNOTE.TXT and many developers and archives refer to it as "the ZIP specification." ZIP stores the file data, indices in the format of a parallel local header and a central directory, and an archive footer, the last of which is required.

The central directory is the ZIP archive’s most important feature. It groups together record data about every file, such as filename, compression method, and relative location in the archive. Like the whole ZIP format, the central directory records are standardized and indexed in a defined order making them straightforward to parse and store for extraction or decompression. But the central directory while integral, is not the only feature.

ZIP's predictable structure, open documentation, and ease of use cross-platform has made it a widely recognized and used file packaging, compression and archiving solution. You can trust almost any PC, Mac, web, or archive service will read a ZIP archive. The archive format's major drawback is mild compression ratios - ZIP was not designed to be the most compressed, but the most portable.

Tar Plus gzip: Packaging First, Compression Second

The gzip format is a compression format by itself, but you are probably more likely to see it in use with tar. Tar creates archives of all sorts, as distinct from compression, grouping files into a nominal directory tree in one tar file. Then, tar calls a packer to run over the archive and internally compress it.

When tar needs to compress an archive, it uses the -z or —gzip flag to call gzip, which compresses the files in the archive before tar packages them. Tar by its design was not made to be compressed. Its archives preserve metadata as much as the underlying file system used to build the tar archive does. So a gzip file has all the individual file names, permissions and paths in the originating file system, but cannot add to or alter them in the compressed archive.

7Z as Compression-First Archiving

7z extends the same architecture concept as trade-offs. 7z archives can contain files compressed by a wide range of compression algorithms but those are not files - they're collections of compressed blocks. An archive decompresses one block at a time but cannot skip to decompression locations. The decompression speed compared to gzip, bzip, and ZIP is. Compression speed and ratio create another tradeoff: the slower you compress, the faster you decompress and get better ratios.

Why the Format Choice Matters in Practice

Knowing what each archive format does and its pros and cons is critical when choosing one to meet your needs. ZIP is a reliable go-to for exchanging or sharing a set of files — it is supported across platforms and with all major archive tools. Tar, meanwhile, preserves the names, permissions and organizational structure of the files you select, but compresses less effectively than ZIP after. 7z, on the other hand, uses the most advanced compression algorithms available with strong compression, but compression efficiency among the three. And it sacrifices the ability to access file information, which means 7z makes it hard to browse the contents of archived files. A ZIP archive, meanwhile, stays invisible until you decompress and extract.

The differences in cost add another factor. ZIP and tar archives are typically faster to compress and decompress, but 7z archives often take longer to extract, especially when they have been compressed with the highest settings. This is because 7z uses a different compression algorithm for each file, and the order in which files are decompressed can affect the total time.

The differences in cost add another factor. ZIP and tar archives are typically faster to compress and decompress, but 7z archives often take longer to extract, especially when they have been compressed with the highest settings. This is because 7z uses a different compression algorithm for each file, and the order in which files are decompressed can affect the total time.

What the Docs Can't Settle, tar only preserves access to files as the archive was made, but after it is compressed, the file names, permissions, and paths are no longer available. Once compressed, it can only be read from start to finish with no option for extracting a specific file from the middle of the archive without first decompressing the whole archive., 7z archives can contain files compressed by a wide range of compression algorithms but the archiving and compression of files is entirely separate from each other. Unlike ZIP, 7z doesn't put file metadata or a central directory in each file: it tries to compress the entire archive into a single solid block. This makes 7z archives extremely efficient, but also hard to open when you don't want to decompress the whole archive. Finally, while 7z can compress files with a wide range of compression algorithms, not all of them are supported by all operating systems. For example, 7z files compressed with LZMA2 or PPMd are not recognizable to macOS or iOS archive utilities.

Bottom Line: No One Size Fits All

ZIP, 7z and tar.gz are designed for very different uses and have very different trade-offs. ZIP is a cross-platform archive format with relatively mild compression but strong compatibility. Tar plus gzip pairs an archive format with a compression format to preserve file directory organization in the archive with mild compression and reasonable speed and efficiency, but no ability to access random files without decompression. 7z uses advanced compression algorithms optimized across the whole archive to yield the best compression ratios of the three, but the flexibility and portability loses most random-access ability and archives take longer to decompress. In the end, which format you choose depends on your specific needs and priorities.