Data Compression: Something for Nothing
Emma was gratified, and would soon have shewn no want of words,
if the sound of Mrs Elton’s voice from the sitting-room had not
checked her, and made it expedient to compress all her friendly and
all her congratulatory sensations into a very, very earnest shake of
—JANE AUSTEN, Emma
We’re all familiar with the idea of compressing physical objects: when you try to fit a lot of clothes into a small suitcase, you can squash the clothes so that they are small enough to fit even though they would overflow the suitcase at their normal size. You have compressed the clothes. Later, you can decompress the clothes after they come out of a suitcase and (hopefully) wear them again in their original size and shape.
Remarkably, it’s possible to do exactly the same thing with information: computer files and other kinds of data can often be compressed to a smaller size for easy storage or transportation. Later, they are decompressed and used in their original form.
Most people have plenty of disk space on their own computers and don’t need to bother about compressing their own files. So it’s tempting to think that compression doesn’t affect most of us. But this impression is wrong: in fact, compression is used behind the scenes in computer systems quite often. For example, many of the messages sent over the internet are compressed without the user even knowing it, and almost all software is downloaded in compressed form—this means your downloads and file transfers are often several times quicker than they otherwise would be. Even your voice gets compressed when you speak on the phone: telephone companies can achieve a vastly superior utilization of their resources if they compress voice data before transporting it.
Compression is used in more obvious ways, too. The popular ZIP file format employs an ingenious compression algorithm that will