A file transfer protocol refers to the method used to transfer files across a network. To enable file transfer to and from a host system a good terminal emulator must support a wide range of protocols to cater to the needs of any number of differing host systems. We take a tour through TTWin’s file transfer options.

Which file transfer protocol shares it's name with a famous green muppet?
Which file transfer protocol shares it's name with a famous green Muppet?


The grand daddy of file transfer protocols, FTP was first mooted in 1971 and has undergone several revisions since that time. FTP is available across numerous host systems and devices and is still widely used today. While web browsers are primarily concerned with viewing data and web pages via the HTTP protocol many also include basic support for FTP transfer.

Today, most users will be familiar with modern GUI based FTP clients however the original FTP clients were entirely terminal and command line based utilities.

Like Telnet, FTP was not designed to encrypt traffic which, in modern times has quite rightly lead to concerns with data security.


SFTP stands for SSH File Transfer Protocol (or occasionally this is interpreted to be Secure File Transfer Protocol), but despite the name it is not merely a secure version of FTP. SFTP is, in fact, an entirely different protocol, distinct from FTP despite the fact that they are functionally similar.

SFTP addresses security concerns in adding the capability to work with underlying secure protocols such as SSH and encrypts both commands and data transfer.


The Kermit  file transfer protocol is a popular file transfer protocol originally developed in the early 1980s at the Columbia University for use among students, faculty and staff. It now has world-wide support on most types of computers.

Kermit is independent of the underlying communications protocol, meaning it can be run over any transport protocol available in Turbosoft’s range of terminal emulation software.

And yes, the protocol is named after that famous green Muppet!

XModem, YModem and ZModem

These three related public domain protocols represent an evolutionary line of file transfer protocols originally designed to work with serial connections and packet switched networks such as x.25. Many old time users will have first encountered one of the three when transferring files on old Bulletin Board Systems, or BBSs - multiuser systems which predated the World Wide Web.

Whilst initially used by hobbyists on BBSs, implementations of these protocols have been created for many host systems.


Originally developed in 1977 by Ward Christensen , whom among other things was the operator and developer of the first BBS software. Consequently the protocol became particularly popular amongst this type of user.

Variants of XModem such as XModem/CRC, XModem-1k and SEAlink made improvements to error checking and transfer throughput.


YModem was developed as a successor to XModem and is similar to its predecessor. It uses larger block sizes (the individual packets or chunks of data sent) along with error checking and correction.

Perhaps most significantly YModem includes support for batch transfer and wildcard (*) usage in selecting files, allowing users to send multiple files in a single request. XModem, on the other hand, allows only one file per transfer.


ZModem was a further evolution on earlier protocols such as YModem and XModem and was particularly popular during the 1980s and early 90s. It was significantly faster that its earlier competitors. During the intervening time between the release and popularization of XModem and YModem, network speeds had greatly improved courtesy of enhanced modem devices. ZModem allowed users to make the most of the that speed increase when transferring files.


The IND$file protocol is closely tied to IBM hosts in that it was originally designed to facilitate file transfer between an IBM mainframe and an IBM PC utilizing 3270 emulation. Due to it’s narrow focus you are unlikely to encounter IND$File outside software such as a Windows terminal emulator.

TTWin 4 is Turbosoft's premier terminal emulation software for Windows operating systems.

With support for 80+ terminal types, secure SSL3, SSH and SFTP along with macro and scripting support, TTWin4 is a comprehensive terminal emulation solution for superior host connectivity.

For product information, free trial software and technical specifications, visit the TTWin 4 product page.