7Z to TAR Converter

What is 7Z to TAR Conversion?

Converting 7Z to TAR is the process of repacking data from a modern compressed archive into a classic Unix family archive container. Unlike 7Z, the TAR format does not apply any compression at all. It is a continuous stream of 512 byte blocks where every file is preceded by a header carrying metadata: name, size, permissions, owner, group, timestamps. The very name TAR comes from Tape ARchive - the format was designed in 1979 for sequentially writing data to magnetic tape on Unix V7.

The defining feature of this conversion is that the resulting file becomes substantially larger than the source. While 7Z with the LZMA2 algorithm compresses data 2-10 times, TAR stores content in its raw form. This is not a drawback but a deliberate choice: TAR is needed in situations where compression is either no longer relevant or will be applied separately by another tool down the pipeline. Unix philosophy says each program should do one thing well, so archiving and compression are split between different utilities.

During conversion, the contents of the 7Z archive are decompressed from LZMA2 blocks into the original bytes, after which all files and directories are sequentially packed into a TAR stream with the full set of POSIX attributes restored. The resulting TAR can be opened by any Unix system through native tools, piped to other utilities, or used as an intermediate stage in backup or deployment scripts.

Technical Differences Between 7Z and TAR Formats

Algorithms and Storage Principles

7Z is a container with built in compression. Data inside passes through a chain of transformations: filtering (BCJ, delta), LZMA2 compression, optional AES-256 encryption. The LZMA2 algorithm uses a dictionary up to 1 GB and adaptive range coding. In solid mode, all files are treated as one long byte stream, which is especially efficient for collections of similar documents.

TAR is a pure archival format with no compression. Every archive entry is stored as a record: a 512 byte header followed by file content padded to a 512 byte boundary. The header includes the file name (with long names supported through GNU or PAX extensions), the size, permissions and timestamps in octal form, the record type (regular file, directory, symlink, device), the owner and group identifiers, and the header checksum.

Capability Comparison Table

Size Comparison: Real Examples

Size relationship between 7Z and TAR for typical data sets:

For already compressed data (photos, video, audio), the difference is small because 7Z could not compress them much in the first place. For text data, source code, logs, and database dumps, the size growth is dramatic, which must be considered when planning disk space.

When 7Z to TAR Conversion is Necessary

Integration with Unix Tooling

TAR is the native format of the Unix operating system family, and many scenarios in this environment specifically require it:

• Backup systems - tools like dump, restore, rsnapshot, BackupPC expect a TAR stream as input.
• Application deployment - the standard way to deliver a distribution to a server is to prepare a TAR with the file tree and unpack it into the target directory.
• File system migration - when moving data between servers, TAR preserves the full set of attributes, which is critical for system files.
• Docker image creation - the docker import command accepts a TAR file containing the root file system of the container.
• Source code tarballs - projects using autotools expect source code as a TAR archive.

Preservation of POSIX Attributes

If the source 7Z contains files from a Unix system, it is important to transfer them with the full set of system metadata:

• Access permissions - chmod modes (rwxrwxrwx) are stored in octal form in each entry header.
• Owners and groups - UID and GID, as well as user and group names, are recorded in the archive.
• Timestamps - mtime is written in each header, and PAX extensions can add atime and ctime with nanosecond precision.
• Special files - block and character devices, FIFOs, and sockets are preserved as corresponding record types.
• Hard and symbolic links - archived with target path references, without duplicating content.

Use as an Intermediate Format

TAR is often a stage in a data processing pipeline followed by an external compressor:

• TAR + gzip through tar | gzip - quick packing with acceptable compression for everyday tasks.
• TAR + bzip2 - moderate to strong compression for distributions and research data.
• TAR + xz - maximum LZMA2 compression for long term archives and Linux repositories.
• TAR + zstd - modern fast compressor from Facebook with flexible compression levels.
• TAR + streaming - the archive can be sent over the network through ssh without intermediate files: tar cf - dir | ssh host 'tar xf - -C /path'.

Incompressible Data

If an archive contains already compressed files (JPG photos, MP4 videos, MP3 audio, DOCX documents), recompressing through 7Z gives negligible benefit but wastes time on compression and decompression. TAR is the more logical choice in this case: the same bytes without CPU overhead.

Conversion Process: What Happens to the Archive

Transformation Stages

1. Reading 7Z metadata - the archive header is analyzed to extract the file list, compression methods of each block, encryption information, and checksums.

2. LZMA2 decompression - compressed blocks are expanded into the original bytes. With solid compression, the entire block is decompressed even if only one file from it is needed.

3. File tree reconstruction - names, paths, and attributes are restored into a hierarchical directory structure.

4. TAR stream formation - for every file a 512 byte header is generated with the name, size, permissions, owner, timestamps, header checksum, and record type.

5. Content writing - after the header comes the file content padded with null bytes up to the 512 byte boundary.

6. Trailing blocks - two empty 512 byte blocks of zeros are written at the end of the TAR archive to mark the end of the archive.

What is Preserved and What Changes

Preserved:

• File and directory names with full paths
• Content of all files (byte for byte)
• Directory structure of any depth
• Modification timestamps
• Access permissions and owners (if present in the source archive)

Changed:

• Archive size (grows manyfold due to absence of compression)
• Storage method (compressed blocks become a sequence of bytes)
• Checksums (CRC-64 in 7Z is replaced with the simple header checksum in TAR)
• Access type (random in 7Z, sequential in TAR)

Not transferred:

• Encryption (TAR does not have it in the standard)
• Solid compression mode (the concept does not exist in TAR)
• Extended Windows attributes (NTFS specific)

Comparing TAR with Other Formats

TAR vs ZIP

ZIP is more convenient for mixed environments, TAR for native Unix tasks.

TAR vs CPIO

CPIO is an alternative Unix archive format used in RPM packages and initrd images.

TAR won mass adoption thanks to its convenient interface.

TAR vs Modern Containers

• TAR + compressor - time tested solution, flexible and compatible.
• SquashFS - compressed file system that can be mounted, but requires kernel modules.
• Disk image - dd, ddrescue for byte for byte copies, without selective recovery.

TAR remains the universal minimal tool for packing a hierarchy of files into a single stream.

TAR Compatibility and Support

Operating Systems

TAR was originally created for Unix and is available everywhere in this ecosystem:

• Linux - the tar utility is part of the standard set in any distribution (GNU tar in most, busybox tar in minimalistic ones).
• macOS - bsdtar is present in the system out of the box and handles TAR fully.
• FreeBSD, OpenBSD, NetBSD - bsdtar is built in and supports additional formats.
• Windows - starting with Windows 10 1803, the system has the tar command based on bsdtar.
• AIX, Solaris, HP-UX - TAR is present in all commercial Unix systems as a standard tool.

Format Specifications

Several TAR dialects exist, differing in how metadata is stored:

• V7 - the original Unix V7 format, simple, with a 100 character name limit.
• USTAR - POSIX 1003.1-1988 extension with names up to 255 characters and an extended set of fields.
• GNU tar - GNU extensions for long names, sparse files, and incremental backups.
• PAX - POSIX 2001, the most modern format with arbitrary metadata in headers.

Modern tar implementations work with all dialects, so TAR compatibility between different systems is very high.

Programming Languages

Working with TAR is built into many standard libraries:

Limitations and Alternatives

When Converting to TAR is Not Optimal

• Internet transfer - uncompressed TAR is many times larger than 7Z, slowing down the transmission.
• Storage on a limited disk - if space is critical, choose a compressed variant (tar.gz, tar.xz, tar.bz2).
• Archives for Windows recipients - if the recipient works on Windows and does not use tar, ZIP is more appropriate.

Alternative Scenarios

• 7Z to TAR.GZ - universal compressed Unix format, balance of size and speed.
• 7Z to TAR.XZ - maximum LZMA2 compression like the source 7Z but in a Unix wrapper.
• 7Z to TAR.BZ2 - strong compression, classic of Unix distributions of the 2000s.
• 7Z to ZIP - for compatibility with Windows and web services.

Conversion to plain TAR is justified when an uncompressed container is specifically needed for further processing in scripts, pipelines, or automation systems.