Any word on the Multics revival front?

Dave G4UGM dave.g4ugm at
Sat Mar 12 14:13:04 CST 2016

> >
> Multics includes a GCOS (6 I think) emulator which allows some GCOS
> programs to run under Multics. (The GCOS emulator copies the GCOS
> program to a segment, and executes the segment in BAR mode with an
> offset of 0; the GCOS application does OS calls with the MME (Master Mode
> Entry) instruction. The GCOS emulator intercepts the MME calls with Multics
> exception handler, deciphers what the call wants, does it, and continues the
> GCOS program.

I assume NOT GCOS 6 as that ran on the DPS6 mini and would need instruction emulation as well as MME. 
Most likely GCOS 3, usually just known as GCOS which was the operation system that ran on the GE600, GE600, L66/L6000/DPS300,  
i.e. the hardware from which the multics machines were derived.
MME is/was the equivalent of the IBM SVC (supervisor call) instruction...
.. not surprised it runs more quickly. GCOS 3 is only a swapping environment AKA OS MVT. Multics is true virtual
Same effect could be observed on IBM Mainframe. Running DOS VSE under VM/370. It ran faster...

> Several of the GCOS applications provided as part of the Multics distribution
> work; such as the DN355 cross assembler. (Let's see: running a cross
> assembler under a GCOS simulator running under Multics, which is running
> on emulated hardware. </scratch head>).

If the instruction set is similar it is not really that contrived. The DN355 cross assembler is written in L66 code. Multics just needs to emulate the system calls.
Just about the same as running MVT programs under VM or MTS on Hercules. For really weird try running the IBM1401 emulator on Hercules on X64...

> There is a also the GCOS TSS subsystem which is an interactive programming
> environment supporting several languages (Multics includes the BASIC and
> FORTRAN runtimes). Sadly, there remain some emulator bugs that are
> causing some failures under TSS; and lacking the source code for TSS, it is
> proving to be an intractable issue.

I wonder if my memory can be jogged. Sadly I no longer have the materials from the TSS internals course I went on in Holland...

> -- Charles


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