[Simh] On {O,D}DDT

[Paul Koning]

> On Jan 21, 2016, at 2:27 PM, Timothe Litt <litt at ieee.org> wrote:
> 
>> ...
> An early DDT manual (~ 1970, but I've lost the colophon page) explains the DDT situation thusly:
> 
> INTRODUCTION
> DDT-10 (for Dynamic Debugging Technique) * .... long page
> 
> In very small print, smaller than I can reproduce here:
> *Historical footnote: DDT was developed at MIT for the PDP-1 computer in 1961.  At that time DDT stood for "DEC Debugging Tape".  Since then, the idea of an on-line debugging program has propagated thoroughout the computer industry.  DDT programs are now available for all DEC computers.  Since media other than tape are now frequently used, the more descriptive name "Dynamic Debugging Technique" has been adopted, retaining the DDT acronym.  Confusion between DDT-10 and another well-known pesticide, dichloro-diphenyl-trichloroethane (C14H9Cl5) should be minimal since each attacks a different, and apparently mutually exclusie, class of bugs.
> 
> Oddly enough, this paragraph subsequently caught the attention of folks who had power, but not much humor.  So it was removed.  But it stuck with me, and is one of the few chemical formulae that I always have instantly to hand.

Neat.  "Mutually exclusive"?  I suppose in those days; earlier, not necessarily, consider the famous story about the first bug as reported by Cmdr. Grace Hopper.

I remember PASDDT.  And yes, various PDP11 ODT flavors existed; the original had rather primitive command parsing, which is why there were odd things like ;B to remove all breakpoints.  As I recall, the original DOS ODT worked that way, and perhaps the early (V2 era) RT11 ODT as well.  Later versions with slightly more available memory were friendlier, which is when removing breakpoints became simply B without the odd semicolon.

> ...
> The other somewhat amusing thing is that DDT's adoption of the <ESC> (echoed as '$') key required a lot of explanation in the manuals, as various models of TeletypeTM caused keys located in the upper left corner of their keyboard to emit different codes -- or the same codes, with different labels.  The monitor had SET TTY commands to map these down to <033>.

Oh yes.  ALT MODE and ... what was the third possible label?  SEL?

While we're on the subject of oddball disclaimers: the RSTS monitor (kernel) debugger was originally a hidden feature, in V4A.  A couple of releases later it became slightly less hidden.  There was a manual for that debugger, which described some of the additional things it could do (like direct examination of data on RK05 disk).  The manual title page came with what looked like a standard DEC copyright / license disclaimer of that era, until you read it carefully:

The material included in this document, limited to but not including,
construction speeds and operating purposes is for instruction times
only. All such claim is material without notice, and is bound to
change the subject.

The standard text of those days (as seen in published RSTS V4 manuals) looks like this:

This document is for informational purposes and is subject to change
without notice.  DEC assumes no responsibility for the use or
reliability of its software on equipment which is not supplied by DEC.

	paul