By c-emmons -

When transferring files, several users seem to have trouble figuring out why such things as images do not send over properly.  A reason for this may be due to the fact that the file could be corrupted by using the wrong type of codes.  Rule of thumb is that if it does not work, you probably corrupted it through your transfer.  Many systems today make it easy to send files without worrying about corruption, but lets take a step back to look at the variations between ASCII and binary transfers.

Binary is the number system that is based on 2, referring to numeric information.  It uses all 8 bits in a byte.

ASCII is the American Standard Code for Information Interchange, or simply the  code that computers have been using to store text for decades.  It is used to code for text only.  If sending an HTML document for example, use the ASCII mode.  It is a limited transfer system because it only uses 7 of the 8 bits in a standard byte.  When it was first created, this was an adequate amount and was run because of the price of computer memory.  The modem speeds then were also much slower, allowing 7 bits instead of 8 made the transfer more rapid.  However, if you were to send something that utilized all 8 bits, 1/8 on the content would be lost.  So the big question here is why do we even bother with ASCII any longer when binary transfers allow for all 8 bits in a standard byte…

If you transfer using ASCII, both FTP clients and servers will translate any symbols into the native language of the computer recieving.  This will rid files that look to have garbage in them or appear to be a long line.  Overall, if sending an HTML file it is safest to used ASCII.  You can send it via binary transfer but you may mess up the file a bit.  Keep in mind if you use a command-line FTP client the default mode is ASCII.

WS_FTP has an Auto mode.  If this is checked, it does not affect the status of the ASCII or binary mode.  This mode helps to send files in either the binary or ASCII mode, whichever is more effective.  This is accomplished by going under the Options dialog, clicking Extensions and filling in the rest.

To summarize, a file that is simply text, HTML, postscript or EBCDIC should be transferred using the ASCII mode because transferring in binary mode could damage the file.  A file that had compressed (.exe, .jpg, .bmp), a bitmap, or an executable should be transferred in binary mode.  Furthermore, keep in mind is the growing system of Unicode.