Kermit (protocol)

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For other meanings see Kermit.

Kermit is a computer file transfer/management protocol and a set of communications software tools; it provides a consistent approach to file transfer, terminal emulation, script programming, and character set conversion across many different computer hardware and OS platforms.

The Kermit protocol allows for transferring text and binary files on both full-duplex and half-duplex 8 bit and 7-bit serial connections in a system- and medium-independent fashion, and is implemented on hundreds of different computer and operating system platforms. On full-duplex connections, a sliding window protocol is used with selective retransmission which provides excellent performance and error recovery characteristics. On 7-bit connections, locking shifts provide efficient transfer of 8-bit data. When properly implemented, as in the Columbia University Kermit Software collection, performance is equal to or better than other protocols such as ZMODEM, YMODEM, and XMODEM, especially on poor connections. Unlike XMODEM and its successors, Kermit can be configured to run on connections over Statistical Multiplexors and the like, where some control characters may not be transmissible.

Kermit was developed at Columbia University in 1981 to allow students to use removable media on microcomputers (initially Intertec Superbrains running CP/M) to hold files from IBM mainframes and DEC DECSYSTEM-20 machines running the TOPS-20 operating system. IBM mainframes used an EBCDIC character set and CP/M and DEC machines used ASCII so conversion between the two character sets was one of the early functions built into Kermit.

CP/M machines used many different floppy disk formats, which meant that one machine could not normally read disks from another CP/M machine. PIP with a very low baud rate (because it had no built-in error correction) was used to transfer a small simple version of Kermit from one machine to another over a null modem cable, or failing that, a very very simple version of the kermit protocol could be hand coded in binary in less than 2K using DDT, the CP/M Debugging Tool. Once that was done the simple version of Kermit could be used to download a fully functional version. That version could then be used to transfer any CP/M application or data.

Over the more than 20 years since its inception, the Kermit protocol has evolved into a worldwide de facto data communications standard, and the software has been used for tasks ranging from simple student assignments to solving compatibility problems aboard the International Space Station.^[1] It has been ported to a wide variety of mainframe, minicomputer and microcomputer systems (some even say that C-Kermit is the second most portable program in the world, after hello world programs);^[2] most versions had a user interface based on the original TOPS-20 Kermit. The MS-DOS version of Kermit was developed in 1983. Later versions of some Kermit implementations also support network as well as serial connections.

Implementations that are presently supported include C-Kermit (for Unix and OpenVMS) and Kermit 95 (for versions of Microsoft Windows from Windows 95 onwards and OS/2), but other versions remain available as well. The Kermit protocol can still be used as a bootstrap and there is an apocryphal story about its legendary portability: "If your toaster has a microchip in it, someone somewhere has probably ported Kermit to it".

[edit] Muppets and copyright

Kermit was named after Kermit the Frog from the Muppets. The program's icon in the Apple Macintosh version was a depiction of Kermit the Frog. A backronym was nevertheless created, perhaps to avoid trademark issues, KL10 Error-Free Reciprocal Microprocessor Interchange over TTY lines.