36bit still in use ?

Rich Alderson RichA at LivingComputerMuseum.org
Thu Dec 4 14:38:13 CST 2014

From: Lars Brinkhoff
Sent: Thursday, December 04, 2014 3:21 AM

> Johnny Billquist <bqt at update.uu.se> writes:

>> As far as I can recall, the TOAD-1 is not compatible with the
>> KL10B. I don't remember what the differences were, but I understood
>> that TOPS-20 had to be modified in an incompatible way to run on it.

> Right, it's not entirely compatible in executive mode.  But it is in
> user mode (well, probably apart from some minor details).

The biggest detail in user mode is that the entire 30-bit address space
is available to user programs, where the Model B KL-10s provided a 22-bit
physical address and a 23-bit virtual (in TOPS-20 from v4 and in Tops-10

The user model is easily seen in TOPS-20 v7+ when invoking DDT:  There is
a switch on the DDT command /USE-SECTION, the value of which is limited on
the KL to section 37 (octal), but can be up to 7776 on the Toad-1.

(Section 7777 is a magic value in the Toad architecture.)

The Toad-1 Architecture Reference Manual is available via anonymous FTP in
PDF, Postscript, and TeX DVI formats at Toad-1.LivingComputerMuseum.org,
in the directory <DOCUMENTATION.TOAD>.  Remember to specify "tenex" or
"type l 8" for the PDF or DVI files.


Rich Alderson
Vintage Computing Sr. Systems Engineer
Living Computer Museum
2245 1st Avenue S
Seattle, WA 98134

mailto:RichA at LivingComputerMuseum.org


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