DecServer 550 chassis

Paul Koning paulkoning at
Mon Oct 19 13:55:24 CDT 2015

> On Oct 19, 2015, at 2:46 PM, Johnny Billquist <bqt at> wrote:
> On 2015-10-19 20:43, Paul Koning wrote:
>>> On Oct 19, 2015, at 2:30 PM, Johnny Billquist <bqt at Update.UU.SE> wrote:
>>> On 2015-10-19 19:42, Paul Koning wrote:
>>>> ...
>>>> CTERM was an attempt to wrap a single protocol around the terribly inconsistent semantics of the terminal drivers in all the DEC operating systems, and to export as much as possible to the server end. ...
>>> An interesting way to describe it.
>>> I've always looked at CTERM as an RPC service that essentially have all the functions of the VMS terminal driver. Makes it easy to implement in VMS, as you have a 1:1 mapping. Makes it horrible for everyone else, since other systems do not have the same functionality in the terminal driver, and now have to implement all the remote procedure calls of the VMS terminal driver, and somehow map that into how the native terminal driver works...
>> You can certainly view it as an RPC, and given that Cterm ended up basically doing VMS, looking at it as the RPC version of the VMS terminal driver is reasonably accurate.  But the original version aimed to support both VMS and TOPS-20 as primary clients, and other operating systems as well.  So it was supposed to be an RPC version of the union of all terminal drivers.  Which means that a full CTERM server (as opposed to client) would be hard to do for everyone, even VMS.
> The amount of swearwords from TOPS-20 people exceed all others combined, in my experience. So if they intended CTERM to be something reasonable for TOPS-20 it was an utter failure. :-)


> And it's really silly and sad, considering that something like telnet is very simple and straight forward, and can be done right on both VMS and TOPS-20, and will in the end work much better for people connecting from one to the other, than using CTERM...
> (I have the same issues with CTERM under RSX. telnet makes so much more sense.)

Sure, telnet in character mode (not line mode) works for everyone because it doesn't try to export any real work to the server end.

For the same reason, the older remote terminal protocols (the set of 4, before Cterm was perpetrated) work great.  Those simply export primitives suitable for the OS in question.  Simple line mode with the ability to switch to character mode for RSTS, character mode all the time for TOPS-20, and a much simpler RSX and VMS terminal driver QIO RPC for those two operating systems.  All these are so easy that RSTS can implement them all, quite unlike Cterm.


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