Compression decreases the size of data.

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72
votes
11answers
3k views

Can zipping a file break it?

I just asked someone to send me a zipped psd file. They declined, citing that zipping a file can break the fonts. I assumed zipping a file is perfectly reversible, hence why it is commonly used. I ...
61
votes
20answers
64k views

Compressing with RAR vs ZIP

A lot of people are compressing files with RAR, sending compressed files with RAR and so on. ZIP is more standard and works on all platforms. Windows users have ZIP included and Linux users have no ...
54
votes
6answers
15k views

Compress and then encrypt, or vice-versa?

I am writing a VPN system which encrypts (AES256) its traffic across the net (Why write my own when there are 1,000,001 others already out there? Well, mine is a special one for a specific task that ...
42
votes
4answers
88k views

How to decompress a .bz2 file

I have a file as: filename.bz2, but I can't figure out how to decompress it. I tried several methods, none of them seems work. I have tried the command: tar xvjf filename.tar.bz2, but it didn't work ...
40
votes
4answers
40k views

How to specify level of compression when using tar -zcvf?

I gzip directories very often at work. What I normally do is tar -zcvf file.tar.gz /path/to/directory Is there a way to specify the compression level here? I want to use the best compression ...
37
votes
8answers
38k views

What’s a good way to extract .rar files on the Mac? [closed]

Anything built-in? (E.g. command line tools.) Any well-regarded software? Update: I like The Unarchiver, but vote up your favourite, or add it as an answer if it isn’t there.
35
votes
5answers
21k views

Pros and cons of bzip vs gzip?

I've known gzip for years, recently I saw bzip being used at work. Are they basically equivalent, or are there significant pros and cons to one of them over the other?
34
votes
5answers
3k views

Why is a 7zipped file larger than the raw file? [duplicate]

Possible Duplicate: Why doesn't ZIP Compression compress anything? I tried 7zipping an .exe file but it actually became larger. Is this the expected result?
29
votes
4answers
12k views

How does NTFS compression affect performance?

I've heard that NTFS compression can reduce performance due to extra CPU usage, but I've read reports that it may actually increase performance because of reduced disk reads. How exactly does NTFS ...
23
votes
2answers
23k views

What do the numbers 240 and 360 mean when downloading video? How can I tell which video is more compressed?

I have downloaded some computer science lectures from YouTube recently. There is usually more than one choice of file size and file format to download. I noticed that for the same video, the ...
23
votes
4answers
38k views

Create a tar file for compressing files and directories on Mac OS X

I'm new to Mac OS X and am not sure how to do this: I have three directories. I want to create a tar/zip file of them so that I can attach them to an email. Any ideas?
22
votes
5answers
1k views

Why doesn't Gzip compression eliminate duplicate chunks of data?

I just did a little experiment where I created a tar archive with duplicate files to see if it would be compressed, to my awe, it was not! Details follow (results indented for reading pleasure): $ dd ...
22
votes
5answers
14k views

How can I open a .7z file in Ubuntu?

How can I open a .7z file in Ubuntu?
22
votes
6answers
2k views

How can I evaluate the best choice of archive format for compressing files?

In general, I've observed the following: Linux-y files or tools use bzip2 or gzip for distributing archives Windows-y files or tools use ZIP for distributing archives Many people use 7-Zip for ...
20
votes
5answers
33k views

What is the maximum compression ratio of gzip?

What is the largest size a gzip (say 10kb for the sake of an example) can be decompressed to?
20
votes
4answers
2k views

Can Double Zipping Cause Problems?

I have a directory that I have been storing a ton of files in. Among the 10ish types of files there are also .zips of other directories. In my personal experience I vaguely remember issues when ...
19
votes
10answers
6k views

Best PNG Compression Software? [closed]

I've just been trying to compress an image with the PNG image format and have had varying results from different applications. For reference, the image I am trying to compress is a screenshot of this ...
19
votes
2answers
12k views

Is zip's encryption really bad? [closed]

The standard advice for many years regarding compression and encryption has been that the encryption strength of zip is bad. Is this really the case in this day and age? I read this article about ...
18
votes
5answers
14k views

Compressing folders on a mac, without the .DS_Store

Is there anyway to get rid of the .DS_Store when compressing a folder on a mac? I work on a mac and send work to clients in zip format, but always get questioned on the .DS_Store folder inside them. ...
17
votes
6answers
20k views

Is it possible to open a self-extracting compressed Windows file on a Mac?

If I have a compressed file that's stored as a self-extracting archive for Windows, i.e., a .exe file, is it possible to convert it to a zip file that can be unzipped under OS X? Alternatively, is ...
16
votes
5answers
30k views

Windows Disk Cleanup: “Compress old files” option

Should I check "compress old files" option while performing disk cleanup on Windows XP? What are the pros and cons? Likewise, there is another option in Local Disk Properties window: "Compress drive ...
15
votes
4answers
26k views

How to make 7-Zip faster

I normally use WinRAR over 7-Zip simply because it's faster and only a little less efficient with compression. I did a few tests on different filetypes and sizes comparing the 7-Zip and WinRAR default ...
14
votes
5answers
39k views

Command to 'gzip' a folder?

I am new to Mac command prompt stuff. How do you create a gzip of a folder in Mac OS X? I was told by a few folks that if you want to create a gzip of a folder you should 'tar' it first and then ...
14
votes
2answers
25k views

Is it possible to execute a file after extraction from a 7-Zip self-extracting archive (SFX) archive?

I'm try to make a compressed deploy-able application. Currently I'm taking a set of files that I've published from my IDE (Visual Studio 2008 - WPF published application) and compressing ...
13
votes
5answers
12k views

What is the quickest, easiest way to compress a mp3 file?

I would like to compress an mp3 file, and I see a lot of references when searching google, but it seems like by now someone must have found something easy and that is guaranteed to work. Compressing ...
13
votes
2answers
35k views

Different compression methods in 7zip: Which is best suited for what task?

So there are different compression methods in 7zip. Which method is best suited for what task? For example: One difference between LZMA and LZMA2 is I can choose all my cpu cores, whereas in LZMA 2 ...
12
votes
4answers
1k views

Why is a FLAC encoded from a decoded MP3 bigger than the MP3?

To be more precise than in the title, suppose I have a MP3 file that is 320 kbps. If I decompress it, then logically, all the data except for roughly 320 kilobits out of each second of audio should be ...
12
votes
5answers
5k views

Fastest GZIP utility

I'm looking for the fastest gzip (or zip) utility. I have a LVM volume which 95% exists out of blank 0's, so compressing that is very easy. I'm looking for the most fastest solution, and don't really ...
12
votes
1answer
239 views

Three formats? Why?

I needed to download the Ruby Source recently from here and it says, "available in three formats" which are .tar.bz2, .tar.gz and .zip. Is there any reason that we need all three formats? At least on ...
12
votes
2answers
5k views

How does file compression work?

So, I realised today I take file compression for granted. The ability to bundle a few files together into one, and have it come out smaller than any of them, is something I just accept as a fact, but ...
11
votes
2answers
418 views

Compressing many similar big files

I have hundreds of similar big files (30 megabyte each) which I want to compress. Every pair of files have 99% of same data (less then 1% difference), so I expect to have not more than 40-50 megabyte ...
10
votes
8answers
10k views

Why doesn't ZIP Compression compress anything?

A 398MB directory was only compressed to 393MB using 7Z and Normal ZIP compression. Is this normal? If so, why do people continue to use ZIP on Windows?
10
votes
9answers
22k views

Highest compression for files(for web transfer)?

I have seen some highly compressed files around, such as 700MB of data compressed to around 30-50MB. But how do you get such compressed files? I have tried using software like WinRAR and 7Zip but ...
10
votes
4answers
9k views

.tar files without directory structure

I'm .taring some files with the path example/super_user/Output.*. The resulting .tar looks like this: + example + super_user - Output.zip - Output.xml - Output.txt ...
10
votes
5answers
6k views

Is there a way of replacing those ghastly 7-Zip default icons?

I like 7-Zip a lot - it's my compression utility of choice on Vista and XP. I have just one problem with it: it's butt ugly. I'm really kind of reluctant to install it on my fresh Windows 7 system ...
10
votes
4answers
5k views

Mac OS X not reporting directory sizes correctly?

In Finder, I've noticed that if I duplicate some .app files (in the Applications folder), Finder will show that the duplicate .app file is not the same size as the original. This file size ...
9
votes
6answers
17k views

How do I uncompress vmlinuz to vmlinux?

I have already tried uncompress, gzip, and all other solutions that come up as google results and these have not worked for me. To get just the image search for the GZ signature - 1f 8b 08 00. ...
9
votes
4answers
9k views

How to obtain maximum compression with .tar.gz?

The way i understand the use of tar + gzip is that tar is normally used to consolidate a grouping of files into a single file, then gzip is used to compress that file. I recently learned that tar can ...
9
votes
3answers
14k views

7-Zip compression on multi-core computers

Does 7-Zip take advantage of multiprocessor or multi-core systems when compressing? For example, would there be a close to 16 times speed-up on a 16 core system assuming no disk or memory ...
9
votes
4answers
31k views

What are the best options to use when compressing files using 7 Zip?

I often have to gather log files and upload them to a central server (Owned by another company). The central server has a size limit of the file, so I am trying to create the smallest file possible ...
9
votes
1answer
222 views

What is the practical value of redundancy in zip files?

How is redundancy implemented in zipping, and how do I benefit from it? I'd assume it consists of something like storing the lookup tables twice so a single defect does not invalidate the whole rest ...
8
votes
2answers
24k views

How to set password on already existing winrar archive and encrypt it also?

Not when creating new archive, but on existing archive. I would also like to know how to do that in other archiver.
8
votes
4answers
3k views

How can I compress a file on Linux in-place, without using additional disk space?

I've got a 100GB drive that has a 95GB file. I need to free up some space on the drive (and right now transferring the file off the drive is not an option). The file would compress well with gzip or ...
8
votes
5answers
9k views

How to unpack a chrome theme?

How to unpack a packed chrome theme(*.crx)? Their FAQ states how to pack, but not how to unpack.
8
votes
3answers
4k views

Is there a way to determine the decompressed size of a .bz2 file?

Is there a way to print the decompressed size of a .bz2 file without actually decompressing the entire thing?
8
votes
2answers
35k views

What settings to use when making 7zip files in order to get maximum compression when compressing PDFs?

What settings to use when making 7zip files in order to get maximum compression? I'm compressing PDF documents containing scanned images. I'm thinking about using LZMA2, but I don't know what to set ...
8
votes
2answers
349 views

let tar auto detect compression type when extracting from stdin

I use GNU tar. It can auto detect compression type when compressing/decompressing files. But I need to decompress an archive from stdin and the compress type is unknown. I noticed that tar can give me ...
8
votes
3answers
10k views

How to do “Files to store without compression” in 7-zip?

Is there any way to selectively prevent certain file types from compression in 7-zip, like in WinRAR? I'm trying to compress a huge folder (many gigabytes), and I don't want the already-compressed ...
7
votes
5answers
3k views

Whatever happened to compressed read/write filesystems?

Back in the 90s, my home computer was an Acorn Archimedes. It had on it a piece of software called ArcFS, which allowed you to create compressed archives, a bit like zip files. Unlike zip files, they ...
7
votes
3answers
5k views

How do I convert tar.bz2 to tar.gz?

I'm new in Linux, is this conversion possible? Do I need to compress and decompress all content?