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zip programs - same final file size?


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#1
bufalo

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I tried a few zip programs, but I have one question.

Am I wrong or should the zipped file be smaller than all the other regular files inside of it put together?

I'd imagine it would be, isn't that the point of zipping? I choose the files, zip them. Any idea if I'm doing something wrong?

thanks!
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#2
Retired Tech

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ZIP is a fairly simple archive format that compresses every file separately. Compressing files separately allows for individual files to be retrieved without reading through other data; in theory, it may allow better compression by using different algorithms for different files.

However a caveat to this is that archives containing a large number of small files end up significantly larger than if they were compressed as a single file

http://en.wikipedia....ZIP_file_format
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#3
Neil Jones

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Am I wrong or should the zipped file be smaller than all the other regular files inside of it put together?


In theory yes but it depends what you're zipping.
You only see a reduction in file sizes if what you are zipping contains redundant data. The final results are dependent on what files you are zipping.
You can't compress something any further than it already is (think what happens if you fold a piece of paper in half and half again - eventually you can't go any further) and in some cases attempting to compress what is already compressed may in actual fact inflate it.

The other point of zipping is to download a bunch of files in one go as opposed to downloading them individually.
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#4
bufalo

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Oh, it's abit more complicated than I thought. I have a power point presentation with video that I wanted to email. It is about 64MB and zipped came to about the same. I guess video is difficult to zip.

I thought I just zip the folder and viola! smaller file to email - wrong.
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#5
Retired Tech

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You can use this if the size for e-mail is too large

http://www.yousendit.com/
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#6
bufalo

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thanks, that's what I used in the end. Took forever to upload, but hey, it's free (also, my laptop is a bit slow)
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#7
Retired Tech

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Upload speeds are unfortunately a lot lower usually than download speeds, although the recipient will be able to download it at their line speed
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