In addition to the other comments: you can have an internal memory representation of data be Float32, but on disk, this is encoded through some form of entropy

In addition to the other comments: you can have an internal memory representation of data be Float32, but on disk, this is encoded through some form of entropy encoding. Typically, some of the earlier steps is preparation for the entropy-encoder: you make the data more amenable to entropy-encoding through rearrangement that's either fully reversible (lossless), or near-reversible (lossy).