Convert LZMA to TAR Online (Trading Compression for a Plain, Uncompressed Archive)

Why This Conversion Removes Compression Rather Than Changing It

A .lzma file is compressed data: a 13-byte header describing the LZMA parameters used, followed directly by the compressed bytes themselves, with the actual file content shrunk down through LZMA's dictionary-matching and range-coding process. Plain TAR is fundamentally different — it's an archiving format with no compression logic built into it at all. Tar's job, going back to its original tape-archive purpose, is bundling files together using 512-byte header blocks that record each entry's name, owner, permissions, and size; the data inside those blocks is stored exactly as-is, uncompressed.

Converting a .lzma file to a plain .tar file means decompressing the LZMA-compressed data back to its original, uncompressed form, then wrapping that data in tar's header-and-data block structure. Since the legacy .lzma format holds only a single compressed stream, this conversion typically produces a tar archive containing that one file; if the original .lzma file had actually held a tar stream compressed with LZMA (making it effectively a manually-built .tar.lzma), decompressing recovers that inner tar structure directly, and no further wrapping step is even needed.

Which exact tar header format the wrapping step produces is also worth being specific about, since tar isn't a single fixed layout. The original V7 Unix tar format from the 1970s, the POSIX ustar format standardized in 1988, GNU tar's own extended format, and the POSIX pax format from 2001 all describe slightly different header block layouts, and most modern tar implementations, including GNU tar, default to writing pax-extended headers today specifically because they handle metadata the older ustar layout couldn't, such as file owner and group names longer than 32 characters.

What a Plain Tar Archive Actually Stores

GNU tar's own documentation describes the format as a sequence of 512-byte blocks: a header block per file recording its name, mode, ownership, size, and modification time, followed by the file's data padded out to the next 512-byte boundary, with two all-zero blocks marking the end of the archive. None of that structure does anything to shrink the data — a 100 MB file stored in a tar archive takes up essentially the same 100 MB inside the archive, plus a small, fixed amount of header overhead per entry.

That's precisely the opposite trade a .lzma file makes. The legacy format exists specifically to reduce file size using LZMA compression, at the cost of needing a decompression step before the data is usable again. Converting to plain TAR reverses that trade entirely: the resulting file is typically much larger than the .lzma original, in exchange for data that's immediately readable by any tar-aware tool with zero decompression step required.

One documented technical limit is specific to the original ustar header format: its size field is 11 octal digits, capping any single stored file at roughly 8 gigabytes (2^33 bytes) before the field overflows. GNU tar and the newer pax format both work around that ceiling — GNU tar with its own base-256 size encoding, pax with extended header records — so a very large decompressed .lzma payload doesn't hit that old limit as long as a modern tar implementation is doing the wrapping.

What Removing Compression Gains and What It Gives Up

• Lose — the entire size reduction LZMA provided: a plain tar archive stores data uncompressed, typically making it substantially larger than the original .lzma file.
• Gain — zero decompression time to access the data: extracting from a plain tar archive requires no decoding step at all, unlike LZMA's dictionary-matching decompression process.
• Gain — Unix permissions and ownership recorded directly: tar's own header format stores file mode, owner, and group per entry, none of which the legacy .lzma format's 13-byte header tracks at all.
• Gain — native multi-file support: a single tar archive can hold any number of files and folders; the legacy .lzma format holds exactly one compressed stream.
• Lose — any compression-related settings entirely: concepts like dictionary size, which directly shaped the original .lzma file's compression, simply don't apply once the data has no compression layer at all.
• Gain — sparse-file handling in GNU tar: GNU tar's --sparse option can store files containing long runs of zero bytes efficiently, a capability with no equivalent concept in the single-stream legacy .lzma format.
• Gain — a format any text editor or hex viewer can partially inspect: because tar's header blocks are plain ASCII fields at fixed offsets, tools like file or a hex editor can identify entry names and sizes without needing an LZMA-aware library at all, unlike the binary-only, unlabeled legacy .lzma header.

Tools That Handle Both Sides of This Conversion

GNU tar can create and read plain, uncompressed tar archives directly with no extra flags needed, since that's the format's original, default behavior before any compression option is layered on top. Decompressing the source .lzma file first requires a tool that understands the legacy format specifically — XZ Utils via its `--format=lzma` compatibility option, 7-Zip's own command-line or GUI tools, or Python's `lzma` module with its `FORMAT_ALONE` constant are the documented options for that step.

Plain tar archives themselves are read by essentially every Unix-like system's built-in tar command, by 7-Zip and WinRAR on Windows, and by macOS's Archive Utility, with no special software required beyond what typically already ships on the system. That broad, unremarkable compatibility is really the entire point of converting to plain TAR in scenarios where compression isn't actually needed or wanted for the next step in a workflow.

Windows itself has shipped a native tar.exe since Windows 10 build 17063, an Insider build released in February 2018 that added both `tar` and `curl` as built-in commands — that tar.exe is actually a build of bsdtar, part of the libarchive project started by Tim Kientzle, rather than GNU tar, though the two read and write plain tar archives interchangeably for this kind of conversion. That means creating or opening a plain .tar file on a current Windows machine no longer strictly requires installing 7-Zip or WinRAR at all, though those tools remain the more common route for anyone working through a GUI rather than a command line.

Real Reasons Someone Strips Compression From an Old LZMA File

A documented, recurring reason involves feeding archived data into a pipeline or tool that expects to apply its own compression later, such as a backup system that recompresses everything with its own preferred algorithm and settings — decompressing the legacy .lzma file to plain tar first avoids running compression twice on the same data, which would waste processing time without meaningfully shrinking the file any further.

A second real pattern shows up when the data inside a .lzma file needs to be inspected, edited, or processed by tools that can't read LZMA-compressed streams directly, and decompressing to a plain, uncompressed tar archive is the simplest intermediate step to make that content directly accessible without needing LZMA-aware tooling at every stage of the pipeline.

A third scenario involves transferring data over an already-fast, already-private connection, such as within a local network or between drives on the same machine, where the time spent compressing and decompressing outweighs any benefit from the smaller transfer size — stripping the compression entirely and working with a plain tar archive removes that overhead completely for this specific kind of transfer.

A fourth documented pattern shows up in digital forensics and data-recovery work, where investigators specifically avoid running compressed evidence through additional decompression libraries until absolutely necessary, preferring to work from a plain, uncompressed archive whose bytes can be hashed and re-verified at every stage without a compression algorithm sitting between the analyst and the original data.

Legacy LZMA and Plain TAR Compared Directly

Questions About Converting Legacy LZMA Data to Plain TAR

Will the resulting file be bigger than the original .lzma file?
Yes, typically substantially. A plain tar archive stores data uncompressed, so it generally matches the size of the original uncompressed content rather than the smaller size LZMA compression achieved.

Why would I remove compression instead of keeping the file small?
Mainly to avoid a decompression step in a pipeline that will apply its own compression later, or to make the data directly readable by tools that can't handle LZMA-compressed streams without extra setup.

Does plain TAR preserve file permissions the legacy format didn't track?
Yes. Tar's own header format records file mode, owner, and group for every entry, none of which the legacy .lzma format's 13-byte header has any field for at all.

Can a plain tar archive hold more than one file, unlike the original .lzma file?
Yes. Tar natively bundles any number of files and folders into one archive, while the legacy .lzma format holds exactly one compressed stream and needed a separate archiving step to bundle multiple files in the first place.

Should I compress the resulting tar archive afterward?
Often yes, if the goal is a smaller file for storage or transfer — pairing tar with gzip, bzip2, or xz restores compression using a format that natively supports multi-file archives, unlike the original legacy .lzma format.

Does Windows need extra software to create a plain .tar file now?
Not necessarily. Windows 10 has shipped a built-in tar.exe (a build of bsdtar from the libarchive project) since Insider build 17063 in February 2018, though 7-Zip and WinRAR remain the more common GUI-based route for most users.