Your Internet Consultant - The FAQs of Life Online
The Internet's e-mail system usually handles basic text files nicely, but doesn't reliably handle binary ones. Text messages are called 7-bit files because characters in the low ASCII character set--which contains the letters A through Z, the numbers, some punctuation, and some special symbols--only use seven of the eight bits that make up each byte. Binary files such as graphics images, sampled sounds, Microsoft Word documents, and many others use all eight bits of each byte. The problem is that many of the hodgepodge of computers on the Internet can't handle 8-bit messages, only 7-bit ones. If you send electronic mail that contains a binary (8-bit) file, chances are that by the time it reaches its destination, it will be stripped of all those eighth bits, something that will completely upset your graphics program, sound player, or word processor.
The solution is to convert those 8-bit files to 7-bit ones before the e-mail trip. The recipient of the message must then convert the file back to eight bits before using the data. There are three common schemes for translating between eight- and seven-bit files: binary to ASCII/ASCII to binary (BtoA/AtoB), uuencode, and binhex. You also may stumble upon xxencoded files, a rare conversion scheme that was supposed to be better than uuencode but never seemed to gain wide acceptance.
BtoA conversion is most popular among UNIX folks. uuencoded translations are popular in the UNIX and IBM PC worlds. Binhex files seem to be preferred by the Macintosh crowd. All of these conversion schemes cause the resulting ASCII file to be larger than the original binaries due to the overhead of all that bit shuffling.
To send a binary file in e-mail, both you and the message's recipient must have a utility to translate between one of these formats.