Explain why compressed files take up less space on a hard drive?

General principle of data compression

Data compression is simply the art of organizing information so that it takes up less space. Imagine a wardrobe where you stuff your clothes in haphazardly: it fills up quickly. In contrast, by folding and organizing them better, you can fit more in. It's the same here; we first identify redundant information (that often repeats) or data that can be easily simplified. Then we assign a shortened code to them (a kind of keyboard shortcut, but for your files). The result: a much lighter file that contains the same information, but better organized.

Reduction of redundancies in files

When you look at the data in a file, a lot of information comes up repeatedly. These repetitive elements, called redundancies, take up unnecessary space. Compression techniques identify these repetitions and assign them much shorter codes. For example, if you have a series of ten identical data points, instead of rewriting that data ten times, your system records that data once along with a note that specifies "repeat this ten times." The same goes for certain file structures, like images, where multiple areas contain strictly identical pixels: compression keeps just a reference to those pixels instead of recreating them each time. Fewer unnecessary repetitions inevitably mean a lighter file, resulting in a less filled hard drive.

Effective encoding techniques used

Compression often relies on clever encodings. Among the most well-known is Huffman coding, which assigns short codes to frequent characters and longer codes to less common ones. The principle is simple: fewer bits for what we see often, and too bad for rare letters. Another classic technique is dictionary coding, used for example in the LZ77 algorithm, where repetitive patterns in the file are identified and repetitions are replaced with a simple reference to the first occurrence. Finally, Run Length Encoding identifies long repeated sequences (for example, a series of identical pixels in an image) and simply states how many times a particular element appears instead of repeating it endlessly. These little tricks combined explain why some compressed files take up much less space than originally.

Impact on the storage space used

When you compress a file, it becomes "lighter" because redundant data is removed or optimized. As a result, it takes up less space on your hard drive or USB stick. If a 100 MB file is compressed to 30 MB, for example, you directly gain 70 MB of free space. This allows you to store more photos, documents, or applications. It also avoids the need to frequently buy new storage space, saving you money in the long run. The benefit is twofold: your hardware wears out less quickly, and your data management becomes much smoother.

Differences between lossless and lossy compression

With lossless compression, you retrieve exactly the same data after decompression as you had at the start. Of course, this is essential for files that cannot tolerate any errors, such as computer programs, texts, or certain images (PNG format). On the other hand, lossy compression allows for a slight loss in quality to gain a significant amount of space. This is the case for music in MP3 format or JPEG photos: you lose details considered not too important for the human eye or ear, but it greatly reduces the file size. In short, with lossless compression you keep everything, but you gain less space. With lossy compression, you sacrifice a few minor details to maximize file size reduction, but be careful, it's impossible to go back afterwards!