Hi Bojan, [Tom] >> the very idea of 7zip is to tar first (internally), then compress.
[Bojan] > Very idea of 7zip is a specific compression algorithm, not a way > the compressing utilites work. :) Actually you are BOTH right. As Rugxulo already mentioned, there is a difference between archives where each file inside is compressed separately and "compact" archives. The latter put all files in one big block of data and compress that. The default mode of 7ZIP is to make a COMPACT archive with a SPECIFIC compression algorithm. ZIP is non-compact and otherwise comparable to TAR.GZ in strength of algorithm. So if you compress many similar files, TAR.GZ gives you the smaller archive. More modern algorithms like BZIP2 will often compress data better, but will spend much more RAM and CPU time in doing that. So TAR.BZ2 is smaller than TAR.GZ which uses GZIP. You do not usually have to make a TAR and GZIP or BZIP2 it separately with a pipeline: Both functions are usually combined behind one command, in particular in DOS where pipelines are not efficient to use. In Linux or Windows, it could happen that the modules internally communicate via pipes without you noticing: In both scenarios, you do not need to have the big, uncompressed "throw all files in one TAR" file lying around on your harddisk while processing a TAR.GZ (TGZ) or TAR.BZ2 (TBZ) file, luckily! However, compact archives also have disadvantages: You cannot remove files from them without recompressing the whole thing. Adding files might also work less well than for "uncompact" formats. Each of multiple files archived in a ZIP exists in a separate area of the ZIP, so it is easy to add or remove a file from a ZIP or unpack a single file without having to go through the whole ZIP and unpack all data to find it. As Rugxulo mentions, 7ZIP also supports "less compact" ways of archiving. That could mean storing information about contents in a more accessible way and compressing the big, compact blob of data in not-so-big chunks. This could allow you to unpack only the 10 MB of your 100 MB BIGSTUFF.7Z file where you have that 5 MB COOLDOC.TXT that you want to extract, thanks to some sort of table of contents in the file and thanks to having an uncompression start point every few MB. Note: I simplify here! Regards, Eric PS: Note that the 7ZIP tool HAS an option "delete file from archive" but you will see that this is ONLY happy when used for ZIP files. When used on 7Z or TGZ, it will work worse. ------------------------------------------------------------------------------ Learn the latest--Visual Studio 2012, SharePoint 2013, SQL 2012, more! Discover the easy way to master current and previous Microsoft technologies and advance your career. Get an incredible 1,500+ hours of step-by-step tutorial videos with LearnDevNow. Subscribe today and save! http://pubads.g.doubleclick.net/gampad/clk?id=58040911&iu=/4140/ostg.clktrk _______________________________________________ Freedos-user mailing list Freedos-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/freedos-user
