Why Some Files Do Not Compress Much and What You Can Do About It
You drag a 1 GB folder onto an icon called Compress and end up with a 990 MB archive. It feels like the algorithm failed. It did not; the folder was already close to its theoretical minimum size before you started. Understanding why is the difference between rage-quitting at the progress bar and getting an actually-smaller file out the other end. The core idea: information density Compression works by removing predictable patterns. A file with lots of repetition or structure compresses well; a file that already looks like random noise barely compresses at all. The technical term for that looks-like-noise property is high entropy. Two short examples make this concrete. A 10 MB text file containing nothing but the letter A can compress down to a few hundred bytes; the compressor just records 10 million As and stops. A 10 MB file containing genuinely random bytes will hardly compress at all; any reduction would require predicting bytes that, by definition, cannot be predicted. Every...