In ftp or sftp, we sometimes need to choose between ascii or binary modes. Why don't just do away with ascii?

Question

I know there's a difference between the two modes (in how carriage returns are handled). But what I would like to know is the advantage of offering this binary/ascii option. Is it more efficient to transfer a text file in ascii mode? Otherwise, since text files may also be transferred in binary mode, why don't just do away with ascii mode altogether?

Answer 1

As you know, ASCII transfers are for text only. If you transfer a text file in binary mode from Windows to UNIX, then the resulting file will have the line feeds and end of record markers messed up. The windows file may have had multiple lines/records on the unix side it would be seen as one record (one big long line).

Also, the ascii mode will automatically convert to EBCDIC when transfering a file to an IBM MVS system.

So, basically, the reason is because ascii transfer mode allows you to retain the text records integrity when transfering between differing operating systems.

Answer 2

The reason there are separate ascii and image modes goes back to when FTP was first developed, and there were two different character sets in use: ASCII and EBCDIC. If your computer used ASCII, and you sent a text file to another computer that used EBCDIC, it would be interpreted wrong, so the FTP protocol lets you specify which character set the file is in, so it can convert it to its native encoding. For binary files, however, you have to use image mode to transfer the file exactly octet-for-octet.

Answer 3

I tried to upload some Web pages onto my Web site a few months ago in binary, and the pages would not work. So, I uploaded with ASCII and they worked.