[Simh] DECsys-7 on SimH [was Re: new paper on history of Unix]

Rich Alderson simh at alderson.users.panix.com
Mon Aug 23 18:12:01 EDT 2010

> Date: Sun, 22 Aug 2010 23:34:49 +0200
> From: "dott.Piergiorgio" <dott.piergiorgio at fastwebnet.it>

> Il 22/08/2010 19:11, Rich Alderson ha scritto:

>> I'll do what I can, but there is a problem right up front:  They did not
>> use standard DECtapes!  They wrote huge data blocks containing 8K words
>> so that a memory bank could be filled or dumped in a single operation.

> really marvelous... the only surviving copy of an historical OS is an 
> hacked copy.... and decsys-7 itself having also at least three 
> chronological layers of coding, will be not an easy work figuring out 
> how U of OR has modded the binary tape we have here....

Ah, no, you misunderstand me.  I apologize for misleading you.

The physicists at the University of Oregon did not use DECSYS-7.  They wrote
their own programs, and designed their own data layouts on DECtape.  They
adapted these to the PDP-9/15 Advanced Software System, but they did not
modify the operating system itself, having no need to do so.

They owned DECSYS-7 media, because it came with the system when they purchased
it in 1966 (installation date in March, according to a document in our files).

> This reminds me when, during mid-late 80s, I have written a small piece 
> of SF centered about "digital archeology".. briefly, the plot was around 
> the understanding and use of the humanist methods & tools (philology, 
> collation of editions, textual criticism &c.) by technically-minded 
> people (I'm actually a sort of polymath more humanist than sci/tech...) 
> I guess that this shows how I'm feeling now..

I am an Indo-Europeanist historical linguist by training, as well as a
programmer, systems analyst, computer scientist, and now museum curator and
collections manager.  I think I have some idea of houw you feel. :-)

>> They also had two hardware modes installed on the machine which allow it
>> to execute PDP-9 and bank-mode PDP-15 code, and used the PDP-9/15 operating
>> system, rather than DECsys-7, for most of the system's history.  I'm not
>> sure that SimH can handle their code without some changes--we'll have to
>> see once I can begin imaging tapes.

> Meh, this is an interesting issue in hardware restoration: this specific 
> -7 is the lone surviving -7, and there is the decision of keeping it in 
> its original condition (that is, "standard" PDP-7) or in his actual 
> working configuration.

Al Kossow pointed out two others (I admit I had forgotten the one at CHM),
so I know of four (two in Australia, Tore Bekkedal's in Oslo, and CHM) other
than ours.

                                                                Rich Alderson

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