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Test about Files and compression

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Here there is a little presentation about files and compression

Presentation:

Lossless Compression

Sometimes it´s important to be able to restore the original material when descompressing a file. You can use lossless compression for this.

One way is to put words or other data into a dictionary with a code. Instead of storing thw word many times, you store the code instead.

There are various algorithms for compressing without loss. Well-known examples are...
- LZW ( Lempel-Ziv-Welch) algorithm
- ZIP files.

Lossy Compression

Some of the detail is taken out in lossy compression in order to make the file smaller. The idea is to remove data that matters the least. This means that you can´t recover the original file when usin this type of compression.

An MP3 music file is only about tenth the size of the original CD track. Data is removed that´s considered beyond most people´s perpection, but some people say they cant tell the difference.

JPEG images are lossy. You can control how much detail to lose.

For more information:

Compression

Some files tend to be very big. Music, images and movies in particular can generate huge files.

A photograph can easily be more than 1Mb. A movie can play at 25 frames a second, which might be 25Mb a second.

Structured and Unstructured Files

Some files have an organised structured.Databases are often arranged as a sequence of records. In a relational database, all the records have the same layout and size.

Files

Files are named stores of data on a computer backing store. Like all other computer date, they are streams of bits: Os and 1s. They can represent any form of data, text, numbers, music, images, movies or instructions.

To make it easier for software and humans to interpret the data correctly, certain file types are recognised.

More information: