Reproducing old machines with newer technology (Re: PDP-12 at the RICM)

Chuck Guzis cclist at
Wed Jul 15 16:54:51 CDT 2015

On 07/15/2015 01:30 PM, ben wrote:

> Quick look on the web ... ARG! Max segment length 64K something.

Well, even in the late 70s, 64KB was still a goodly chunk of memory in 
the microprocessor world.  Which reminds me...

To bore you with another STAR tale--the machine had two page sizes--the 
"small" page, which was 512K 64-bit words and the "large page", which 
was 64K words.  What some smart-alec discovered was that in a 512Kw 
system, it was possible (easily) to write an instruction that could 
never get started.  You could have up to 6 addresses in a vector 
instruction (3 operands+3 control vectors).  Storage was managed in 512 
bit "super words".  Start your large-page job, put two of the operands 
near the end of a page and bingo--you get 8 page references just to get 
the instruction started.  Of course, the solution was to sell the 
customer more memory...


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