Talk:Gzip

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[edit] Old Discussion

"Although its file format also allows for multiple such streams to be concatenated together (these are simply decompressed concatenated as if they were one), gzip is normally used to compress just single files."

I don't understand what this sentence is trying to say. --Gbleem 19:08, 15 October 2006 (UTC)

Here's §2.2 of RFC 1952:
A gzip file consists of a series of "members" (compressed data sets). The format of each member is specified in the following section. The members simply appear one after another in the file, with no additional information before, between, or after them.
That is, a member is a compressed file and the gzip format allows one .gz file to contain multiple compressed files. In practice, however, it is always better to use either a ZIP archive or a compressed tar archive to handle multiple files, so people rarely put more than one member in a compressed file. In fact, the gzip program provides no easy way to do that. Furthermore, when used to decompress a .gz file containing multiple members, the program does something quite unhelpful (creates a single file containing the concatenated contents of the original members) instead of (for instance) recreating the original members as individual files.
I hope this helps. Cheers, CWC(talk) 05:22, 16 October 2006 (UTC)

[edit] AdvanceCOMP/7-zip

AdvanceCOMP and 7-zip use a DEFLATE implementation which produces gzip-compatible files with better compression ratios than gzip itself, at the cost of more processor time.

I removed this because 7-zip does not produce gzip-compatible files. Even using the deflate method, 7-zip files cannot be decompressed with gzip. If you contend otherwise, please post the required commands to compress a file with 7-zip and then decompress it with gzip. I used: '7za a test.7z test.bin' then 'mv test.7z test.gz' then 'gunzip test.gz' and gunzip reported: "gunzip: test.gz: not in gzip format". '7za l -slt test.7z' reports "Method = Deflate". I don't know anything about AdvanceCOMP. If you can verify that an AdvanceCOMP-compressed file can be decompressed using gzip, feel free to re-add the part about that program, but please clarify whether *all* or just *some* AdvanceCOMP archives are gzip-compatible, if so. Ramorum (talk) 07:37, 17 February 2008 (UTC)

Hello Ramorum, did you try using the -t switch? This should select the container format; eg. -t7z, -tzip, -tgz (the last should produce gzip encapsulated DEFLATE) using the internal DEFLATE implementation. —Sladen (talk) 15:39, 17 February 2008 (UTC)

[edit] Good source

There's an excellent concise discussion of the specific techniques used in gzip in the book Managing Gigabytes, section 2.6, pp.78–79. It even includes some important implementation details not in the RFC. I'll add some info from there once I've dealt with the more fundamental Ziv-Lempel articles. Dcoetzee 19:37, 9 May 2008 (UTC)

[edit] --rsyncable option

perhaps some discussion of the rsyncable option, which occasionally resets the compressor so that an early change can still leave later sections identical after compression (for smaller deltas), might be worthwhile. I don't know enough to do it myself. —Preceding unsigned comment added by 216.106.175.189 (talk) 19:04, 3 June 2008 (UTC)