Compression decreases the size of data.

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170
votes
7answers
365k views

How to decompress a .bz2 file

I have a file as: filename.bz2 I need to decompress. I have tried the command: tar xvjf filename.tar.bz2, but it didn't work as the file is not a tar file. How do I decompress this file?
131
votes
6answers
18k views

How is PNG lossless given that it has a compression parameter?

PNG files are said to use lossless compression. However, whenever I am in an image editor, such as GIMP and try to save an image as a PNG file, it asks for the compression parameter, which ranges ...
81
votes
11answers
4k 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 ...
76
votes
20answers
101k 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 ...
74
votes
4answers
83k 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 ...
74
votes
5answers
41k 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?
73
votes
7answers
24k 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 ...
70
votes
8answers
94k 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.
42
votes
4answers
24k 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 ...
39
votes
5answers
34k 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. ...
34
votes
5answers
7k 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?
34
votes
4answers
71k 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?
31
votes
6answers
70k 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 ...
28
votes
5answers
64k 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?
28
votes
2answers
74k 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 ...
26
votes
6answers
30k 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 ...
26
votes
3answers
50k 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 ...
25
votes
4answers
40k views

How to obtain maximum compression with .tar.gz? [duplicate]

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 ...
25
votes
7answers
3k 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 ...
24
votes
5answers
7k 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 ...
24
votes
5answers
18k views

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

How can I open a .7z file in Ubuntu?
24
votes
6answers
3k 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 ...
23
votes
2answers
42k 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 ...
22
votes
10answers
7k 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 ...
20
votes
4answers
49k 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 ...
20
votes
3answers
69k 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 ...
19
votes
2answers
15k views

Is zip's encryption really bad?

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
3answers
45k 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.
18
votes
5answers
38k 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 ...
16
votes
6answers
29k 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. ...
16
votes
4answers
33k 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 ...
16
votes
7answers
16k 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 ...
16
votes
5answers
12k views

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

I like 7-Zip a lot - it's my compression utility of choice on Windows. 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 because ...
16
votes
2answers
8k 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?
16
votes
4answers
21k 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 ...
16
votes
3answers
21k 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 ...
15
votes
5answers
10k 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 ...
15
votes
4answers
12k views

Is it safe (or advisable) to compress Windows Installer folder via NTFS compression?

The title pretty much explains the question. Aside from the obvious (speed), is it generally safe or advisable to compress via NTFS compression the C:\Windows\Installer folder given that it's within ...
15
votes
2answers
7k 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 ...
15
votes
5answers
35k views

What if I checked the box “Compress this drive to save disk space” on an SSD?

I was wondering how it would effect an SSD if this was checked: I was just curious whether it would save my SSD disk space?
15
votes
1answer
19k views

How does 'dictionary size' affect compression?

I know that higher size may lead to better compression ratio and vice verca. But is there a way I can decide better?.. since there are so many choices So far I've noticed dictionary size ≈ file ...
14
votes
4answers
46k 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 ...
14
votes
3answers
35k views

What is the cause of a high CPU usage of 'system and compressed memory' in Windows 10?

There is an observation to be made for Windows 10 on my laptop running with 24G memory available, and 2.5G used. There is no 'memory pressure'. Other questions have looked at memory consumption ...
13
votes
8answers
24k 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?
13
votes
4answers
2k 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 ...
13
votes
2answers
14k views

Compress files from OS X terminal?

In the Finder, there is this wonderful ability to right click on a file or directory, select compress from the drop-down, and end up with a zipped file. Is it possible to do the same thing from the ...
13
votes
4answers
8k 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 ...
13
votes
1answer
12k views

How do I rar a file into several parts in Linux?

I want to make a rar file(not tar or gzip) with several parts in linux shell, how can do that please? for example my file is : m.avi - 500mb I want this : m.part1.rar 250mb m.part2.rar 250mb
13
votes
6answers
12k 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.
13
votes
6answers
24k views

How can I achieve the best, standard ZIP compression?

I don't care how long it takes to compress, all I want to achieve is two things: The absolute best possible compression ratio Compatibility with standard readers, such as Windows and WinZip So ...