Tvmama

1 Comment Written by Atila on July 23, 2008 – 5:27 pm

Compressed folders use mathematical and logical tricks to squeeze 10 pounds of stuff into a 5-pound bag, or more precisely something like 10MB of data in a 5-MB folder. The trick involves formulas (called algorithms) that look for repetitive characters or numbers that can be replaced with shorter blocks of data. Compression works especially well with image or sound files. For example, say you had a picture of the front cover of this book. Large sections are made up of nothing more than blank yellow or black background.

The computer’s file describing the cover might start with 10,000 iterations of the 24-bit binary code 111111111111111100000000, which is equivalent to the hexadecimal code FFFF00 (system code for yellow) to describe just the first 10 rows of data from the top. An uncompressed image file, then, might have to use up 240,000 bits (about 30,000 bytes) just to describe those first 10 lines.

But say you used a compression program that analyzed those 240,000 identical bits and instead wrote a description that said: 10,000 * 111111111111111100000000. That instruction might take up just 32 bits of space. One important detail: You need to use the same algorithm to compress and decompress the file. Everything else is handled by the extremely fast computer.

In the early days of personal computing and laptops, hard disk drives were measured in megabytes rather than gigabytes and space was at a premium. And users didn’t have large recordable CDs or huge recordable DVDs to offload files. Older technologies for transmitting files, including dial-up modems, also benefited from any compression; smaller files take less time to transmit than larger ones. Today, high-speed broadband and WiFi networks make that less of an issue.

However, compressed folders and files are still valuable. With Windows XP, compressed files became fully integrated into the OS after being generated previously by third-party add-on programs.