Email 101 Part 6

1. Files that use proprietary formats, such as word-processing programs, spreadsheets, database programs, etc. These files contain formatting (like italics, underlines, etc.) and perhaps graphics, and other goodies beyond the simple text.

2. "Application Programs". These are programs written in (the binary) machine language that your computer understands. They are "compiled" from text files of "source code" written in a programming language. Vendors almost never make their source code available--except for free software, which you may have to compile yourself.

3. Text files that have been compressed to about half their size with one of the popular compression programs. Compression makes texts files binary. Compression doesn't do much for files that are already binary unless the data they contain is very repet.i.tive.

4. Files containing graphics like GIF, TIFF, PICT, or JPEG files.

More on this below.

Transfering binary files is as easy as transfering text files once you understand the potential problems:

1. Most FTP programs start you out in TEXT mode. This means that text files are *translated* when they go from computer to computer on their way to you. This is fatal to binary files because their bit pattern has nothing to do with the groups of eight bits that make up text.

2. Even text files have slight compatibility problems because the three "worlds"--IBM, Macintosh, and UNIX--use a different control character to represent "return", "enter", or "newline." Translation between the different dialects is handled automatically in TEXT mode transfers. It is also the main reason why text files cannot be transfered in BINARY mode.

The two control characters involved are called "linefeed" (LF) and "carriage return" (CR):

IBM PC and compatibles :

Macintosh and VAX :

UNIX :

3. As mentioned above, text files are often compressed to save s.p.a.ce.

This means that you need a program to uncompress them before you read them--and that you have to transfer them in BINARY mode.

The most common compression programs and common file extensions are:

IBM PC and compatibles : PKZIP and PKUNZIP (.ZIP)

Macintosh : Stuffit and UnStuffit archives (.sit)

UNIX : compress and uncompress (.Z) and tape archive (.tar) with both together being most common (.tar.Z or .taz). Note capital "Z".

UNIX also has the gzip/gunzip command pair. gzip files usually have the extension ".z" (*small* z) or ".tgz" if they are also tape archive files.

Fortunately you can usually find free software for you computer that will uncompress formats from other computer models. For current information on compression software, see the FAQ for the newsgroup comp.compression (ftp://rtfm.mit.edu/x.x.x).

4. Conversely, sometimes binary files are converted to a sort of ASCII that looks like gibberish so that they can be mailed or transferred in TEXT mode--but again you need a program that translates them back to binary. Sometimes we encounter the ultimate absurdity, a text file that is compressed then re-encoded as ASCII for mailing.

Actually this makes sense if a large number of related text files are stored in a compressed "archive".

The most common programs for this are:

uuencode/uudecode for UNIX (used for Usenet news postings of binary files and for mailing programs) The file extension (rarely encountered because there is little reason to store files in this format) is ".uue".

BinHex for the Macintosh (.hqx) Often combined with Stuffit (.sit.hqx). This is a common method for distributing all the files that come with a program as a single file.

uuencoded files can be recognized by the fact that every line begins with a capital "M" and is exactly the same length. The file starts with the word "begin" and ends with "end" The translating program needs these words, but nothing above or below them. Often a uuencoded file is split into several parts for transmission and must be rea.s.sembled (and stripped of mail headers, etc.) in a word processing program before it is decoded. If you do this be sure to save the resulting file as a text file and not in the proprietary format of the word processing program!