Kermit Software for the PDP-11


Digital Equipment Corporation's PDP-11 was (and is) a 16-bit mini- or microcomputer used in applications ranging from embedded device control to general-purpose timesharing. Several different Kermit programs are available for the PDP-11.

Kermit-11 is the Kermit software for Digital Equipment Corporation PDP-11 operating systems: RT-11, RSX-11, RSTS/E, IAS, P/OS, and (not a DEC OS) TSX+. Kermit-11 was written by Brian Nelson of the University of Toledo, Ohio, circa 1984-89, in PDP-11 assembly language, Macro-11. Separate programs, listed below, are available for other PDP-11 operating systems like UNIX and MUMPS.

The Kermit-11 source code is available at our ftp site in the kermit/b subdirectory as k11*.mac, and you can find prebuilt-binaries for various operating systems and configurations in kermit/bin/, as k11*.tsk or k11*.sav. If you are unfamiliar with FTP, or have problems with it, READ THIS. There are also various utilities -- hex encoders and decoders, etc -- written Macro-11, Fortran, and Basic in the kermit/b directory, along with all the Kermit-11 text files, whose names all start with "k11".

Kermit-11 can operate in either remote or local mode; that is, it can transfer files when it is on the far end, and it can make connections and enter terminal mode (and transfer files) when it is on the "near end".

The documentation for Kermit-11 is based on Brian's last release (please note that the ".doc" extension was used for plain-text documentation files since long before Microsoft existed, so if your Browser thinks it's some kind of rich-text document that needs a helper application to read it, tell it to just load it directly as plain text, no helper needed).

Installation instructions are also available:

There are separate versions of Kermit-11 for each DEC OS, plus distinct Kermit programs for other PDP-11 operating systems. Originally all the Kermit-11 programs were all built from a common code base. After Brian moved on, some of the Kermit-11 versions took on separate identities that, we hope, will someday be brought back into alignment. The PDP-11 Kermit programs are:

RSX-11, RSX-11/M, RSX-11/M+, Micro/RSX, IAS, and P/OS
Brian's last release, 3.60 from June 1989, is still current for RSX and its cousins. RSX-11/M 4.1, RSX-11/M+ 2.1, P/OS 2.0 or IAS 3.1 or later is required in most cases. This version has some bugs that prevent successful transfers with more modern Kermits, which can usually be worked around by telling one or both Kermit programs to "set attributes off".

RT-11, Pro/RT, and TSX+
A new version, 3.62, for the RT-11 family only, was produced by Billy Youdelman in September 1993 and includes lots of bug fixes and enhancements. Version 3.63 was released 27 September 1997. RT-11 4.0, TSX-Plus 5.0, or Pro/RT 5.1 or later are required. All of the source files are in the kermit/b area as krt*.*. The krt.doc file contains complete installation instructions for RT-11 and TSX-Plus.

The RSTS version was further developed by John Santos in 1996, based on Billy's version, and a test edition of John's improved RSTS version is available. RSTS/E 8.0 or later is required. The source files are in the kermit/test/pdp11/ area as krt*.*.

2.8, 2.9, 2.10, and 2.11 BSD
The 2.xBSD versions are covered by G-Kermit 1.00 and C-Kermit 6.0 rather than Kermit-11. (C-Kermit 7.0 or later, even in a minimal configuration, is too large for the PDP-11 address space.)

G-Kermit is available for Ultrix-11 3.0.

VENIX 1.0 and 2.0
C-Kermit 4.x was buildable for VENIX on the Pro/350 and 380. Versions 5A and later were never tested there, but the C-Kermit makefile still contains the appropriate entries. Unfortunately binaries were not saved.

Bell UNIX V6 and V7
G-Kermit can probably be built for UNIX V6 or V7, but so far we have no reports about it.

A version of Kermit for the MUMPS-11 PDP-11 operating system can also be found at the Kermit archive. It is totally separate from Kermit-11 and C-Kermit. It was written in MUMPS-82 at the New York State College of Veterinary Medicine in 1984 and can be found in the kermit/b area as mp*.*, with documentation in the plain-text mpker.doc file. Nothing has been heard about this version since 1984, when it was submitted; it is completely unsupported. Reports would be welcome.

Others for which no Kermit programs are known to exist
It is a goal of the Kermit Project to unify the divergent Kermit-11 versions, bringing the RSX version up to date in the process but this will require some volunteer effort by PDP-11 aficionados, and no promises can be made.

Kermit-11 Binaries

As noted, all the text files, including source code, documentation, utilities, and so on, are in the kermit/b directory of the Kermit software archive, all sharing the filename prefix "k11". The newer RT/TSX version is in the same directory, but with prefix "krt". The RSTS/E test version is in kermit/test/pdp11. Binaries are in kermit/bin/ and kermit/test/pdp11/bin/. Prebuilt binary executables are as follows; more detailed descriptions can be found in the accompanying installation instructions.

Name Description
k11.tsk Kermit-11 3.60 for RSTS/E 8.0 or later, linked to RMSRES
k11id.tsk As above but with I&D space
k11nrs.tsk RSTS, but not linked with RMSRES
krtid.tsk A test 3.62 version for RSTS, requires I&D space
k11idm.tsk Kermit-11 3.60 for RSX11M+ or Micro/RSX with I&D Space
k11pos.tsk Kermit-11 3.60 For RSX11M+, Micro/RSX, or P/OS, might also work on RSX 3.x.
k11rsx.tsk Kermit-11 3.60 for RSX, not linked with RMSRES
k11sml.tsk Kermit-11 3.60 RSX11M, small executable, tightly overlaid
k11i31.tsk Kermit-11 3.60 for IAS 3.1
k11ias.tsk Kermit-11 3.60 for IAS
k11xm.sav Kermit-11 3.60 for RT-11XM and TSX+.
k11rt4.sav Kermit-11 3.60 for RT-11FB and TSX+.
krt.sav Kermit-11 3.63 for RT-11FB/SB/SJ and TSX+.
krtmin.sav Kermit-11 3.62 for RT-11FB/SB/SJ minimal version
krttsx.sav Kermit-11 3.63 for RT-11XB/XM/ZB/ZM and TSX+.

Native Media

The Kermit Project has no PDP-11 computers in house to make PDP-11-specific formats. We can no longer make 9-track tapes of any kind, and we have never been able to make 8-inch or any other size of PDP-11 format diskette, no RK05, DECtape, etc.

Native media -- RX01, RX50, RK05, DECtape, who knows what else -- might be available from the DECUS library (if it still exits), 219 Boston Post Road, BP02, Marlboro, MA 01752-1850. Write, or call (800) 332-8755, or send Internet e-mail to for further info.

When you can't get PDP-11 Kermit on native media, you will have to find a way to "bootstrap" the appropriate hexified binary onto your PDP-11, along with the dehexifying program, and then use the latter to decode the former (next section).


How to get Kermit-11 onto your PDP-11 if it doesn't already have Kermit or FTP, and nobody can send you a binary on the required media? The precise answer depends on your PDP-11 operating system (RT, RSTS, RSX, etc), but basically involves "capturing" a copy of the appropriate Kermit-11 binary that has been converted to hexadecimal (ASCII) format onto your PDP-11 disk, as well as a copy of the dehexifying program (written in Macro-11, Fortran, or BASIC), and then running the dehexifying program to decode the hexified binary.

For example in RT-11, get the following files in text mode:

Name Bytes Description
krtmin.abs 1122 A short abstract describing KRTMIN
krtmin.doc 4032 Documentation (krt.doc is the complete version if need be)
krtmin.hex 135937 A HEX encoded copy of the Kermit executable image
krtmin.hlp 45137 The HELP command text file
krtmin.ini 185 A sample init file
krthex.mac 9836 The HEX to executable image conversion program (Macro-11)

And then read the instructions are at the top of the krthex.mac file.

Here are the "hex" encoded (i.e. printable text) versions of the executable programs. They are useful if you don't have any way to get binary files onto your PDP-11. Hex files can be "bootstrapped", sent by email, etc.

Name Bytes Corresponding binary Description
k11.hex 286848 Corresponds to k11.tsk. RSTS/E 8.0 or later, RMSRES
k11i31.hex 199296 Corresponds to k11i31.tsk. IAS 3.1
k11nrs.hex 441216 Corresponds to k11nrs.tsk. RSTS/E 8.0 or later, no RMSRES
k11pos.hex 270720 Corresponds to k11pos.tsk. RSX11M, MicroRSX, P/OS
k11rsx.hex 361728 Corresponds to k11rsx.tsk. RSX, no RMSRES
k11rt4.hex 229248 Corresponds to k11rt4.sav. RT-11RB or TSX+
k11xm.hex 233856 Corresponds to k11xm.sav. RT-11XM, TSX+.
krt.hex 236161 Corresponds to krt.sav. RT-11FB/SB/SJ, TSX+.
krtmin.hex 135937 Corresponds to krtmin.sav. RT-11FB/SB/SJ minimal version
krttsx.hex 243073 Corresponds to krttsx.sav. RT-11XB/XM/ZB/ZM, TSX+.

Programs for "dehexifying" the hex files (i.e. converting them back to their original binary executable format) are:

Name Bytes Description
k11hex.bas 2525 RSTS/E 8.0 or later Basic-Plus
k11hex.b2s 2735 VAX Basic and PRO/Basic
k11hex.ftn 3827 Fortran-77 for RSX, RSTS, and RT-11.
k11hex.mac 4042 Macro-11 for RT-11.

Additional Information

Onsite files and links:

Note: .HLP and .DOC are original 1960s and -70s DEC filetypes. If your browser insists on treating them as Windows Help or Microsoft Word documents, your browser lacks a sense of history.

Offsite links:

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Kermit for the PDP-11 / Columbia University / / 4 Dec 2003