Re: Compression Utilities


"Roedy Green" <my_email_is_posted_on_my_website@xxxxxxxxxxxxxx> wrote in message news:96a5021u518df69g4tucqseht3ot3am90k@xxxxxxxxxx
I have benchmarked a number of compression utilities and have posted
the results at http://mindprod.com/jgloss/compressionutilities.html


You mention that it's important that you compress to a format that the recipient can decompress from; have you considered adding to the benchmarks compressions where you create self-extracting archives? E.g. Winzip and WinRar offer to compress to a .EXE instead of .ZIP and .RAR files.

Obviously, the resulting self-extracting archives would probably be platform specific, but this might make sense if what you were archiving were the distribution for a platform specific program anyway.


Microsoft is preposterously inept.. [...] their
compression barely makes a dent in the size.

To be fair, the intent of their "compact" utility is to allow the files to be used without an explicit decompression step, which (AFAIK) none of the other formats (.ZIP, .RAR, .7z, etc) allow. I believe they use something really simple like run-length encoding, to allow for fast decompression, random seeking within the file, and other stuff that one would typically want to do with the uncompressed contents of a file, that might be prohibitively expensive or difficult to do with the compression schemes used by the other formats.

I have some images of CDs on my harddrive which I mount using a CD drive emulator. The "useful contents" of the CDs are relatively small (100MB), but they contain padding files of sizes around 600MB which just contain the byte 0x00 over and over again; the reason for this is to place the useful content near the outer edge of the CD, thus allowing for faster data reads (because when the CD spins at a constant angular velocity, the drive can read from the outer edge faster than the inner edge).

This trick doesn't do anything for when the CD is stored as an image on my harddrive though, so the file is 600MB bigger than it needs to be. If I use the "compact" utility, it does RLE on the padding file to reduce it to just a few kilobytes, and so the image file is down to a more reasonable 100MB size.

- Oliver

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