This is still the preferred backup method for some industries. Historically, data from servers was often backed up onto tape archives, which are magnetic tape devices that can be used to store sequential data. An “archive” on a Linux server in general has a slightly different meaning. The idea of “archiving” data generally means backing it up and saving it to a secure location, often in a compressed format. The dictionary progressively gets more efficient as the process continues. Instead, they analyze the file as they go and rewrite the dictionary based on what data is actually repeated. This means that they do not analyse the entire input file at the beginning and create the “dictionary” of reference substitutions from that. These are actually the two stages that every lossless compression technique uses: map highly repeated values to something which is smaller that can be easily referenced and then change the occurrences of each of those values with the reference.įurthermore, modern lossless compression techniques are said to be adaptive. Think of this process as creating a list of variables that define blocks of data, and then using those variables later on to fill in the program. This allows the computer to store the information on less disk space. It continues on and replaces later occurrences of the pattern with It removes these and replaces them with a placeholder. This type of compression does not use approximations to compress data, and instead uses certain algorithms to recognize repeated portions of a file. Lossless compression is the type that we will cover in this guide. The greater the compression ratio that is used, the larger the range of colors is that will be blanketed in this manner.Īlternatively, a lossless compression method creates a file smaller than the original that can be used to reconstruct the original file. A JPEG compression utility will try to find fields of color that are close enough to one another and replace the entire field with a single color. The more they are compressed, the more significant data is lost and the more the compression will be visible. The higher the compression ratio, the more the compression will start to affect significant portions of the audio.Īnother example of this is JPEG images. The compression may be unnoticeable to the user, but it does not contain all of the relevant information of the original. You can not convert the MP3 back into the same source file later on. This is called a lossy compression method because it really does lose the information from the original file that does not make it into the MP3. This is because an MP3 is created by analysing the waveform of the audio file and basically figuring out which data it can throw away permanently while still retaining the spirit or general sound of the original. This type of compression is fundamentally different than what we will be talking about in this guide. An MP3 is a compressed sound file that is used to create a smaller file from a larger source music file. Let’s take for example an MP3 music file. When discussing compression in regards to computers and file types, the same terms can mean a few different things depending on context. Both of these areas represent opportunities to employ compression techniques. Furthermore, content itself is often repeated. Files are formatted in certain ways that make their general structure somewhat predictable, even if their content varies. Compression and Archival Basicsīefore we jump in to the actual tools we’ll be using, we should define our terms and discuss some of the different characteristics of compression and archiving techniques.Ĭompression is a way of reducing the size of a file on disk using different algorithms and mathematical calculations. We will be demoing these tools on an Ubuntu 12.04 VPS instance, but they will operate pretty much exactly the same on any modern Linux distribution. We will also touch on some associated operations, like archiving, which make our compression tools much more flexible. In this guide, we will discuss some of the different methods of compressing data and talk a bit about some of the trade-offs of various methods. Some of the more straightforward benefits are conserving disk space and using less bandwidth for network communication. There are many reasons why you would want to compress files and directories on a computer.
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