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what constitutes incompressible data?

Thu Apr 26, 2012 9:03 pm

I have seen plenty of ssd reviews and they all say sandforce drives are slower with incompressible data than compressible data.

So what types of files are incompressible data?

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Re: what constitutes incompressible data?

Thu Apr 26, 2012 9:10 pm

Since you don't need a CS explanation, they just mean things that are already compressed, since it's unlikely adding more compression will do much to the filesize as it's already close to optimal.

jpeg and mp3, but not png or wav
rar but not tar

et cetera
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Re: what constitutes incompressible data?

Thu Apr 26, 2012 9:25 pm

Some file formats are more compressible (wav more than mp3) but compresible itself means that the data has a lot of repeating patterns in it that can be substitutes for shorter patterns, or represented in a more compact form.

ie; for an image of 100 by 100 pixels of all the same color, its more efficient to store the image as "100 by 100 of color code" than color code, color code, color code etc... 10000 times.

I have two sandforce drives, and on a practical note, in day to day work, they are much faster than HDD and almost no one would notice the difference in compressed vs, uncompressed files unless they were benchmarking.
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Re: what constitutes incompressible data?

Wed May 16, 2012 6:43 pm

Mp3, Ogg, FLAC, etc are forms of audio compression. Those files are already compressed, so you're not going to get much more (if any) compression on them. Same goes for Jpegs, PNG, and TIFF (image compression formats); rar, tar, zip (general file compression) and most any other media format------unless you know that it's in a raw, uncompressed form (like a .wav).
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Re: what constitutes incompressible data?

Wed May 16, 2012 9:26 pm

@Egglick - Nit-pick: The most common compression algorithms used by TIFF are not very efficient, so the files may still qualify as compressible. I agree with you on the rest.
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Re: what constitutes incompressible data?

Wed May 16, 2012 9:53 pm

One of the dumb things that is quite common is rar compressing video files. They almost invariably end up being larger than the original file.
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Wed May 16, 2012 11:28 pm

Game_boy wrote:
…jpeg and mp3, but not png or wav…

Actually, hi–quality JPEGs are compress–able (using general purpose, loss–less algorithms, like the ones used in ZIP, RAR, and 7zip files); PNG are not compress–able (unless they were created using a lousy application/library).

Try it for yourself.
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Re: what constitutes incompressible data?

Thu May 17, 2012 12:02 am

Stuff that IS compressible:

Executable files (EXE, DLL)
Text (html, code, documents, logs)
Disk images (some ISOs, others already ARE compressed)

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