Transporting an LGP-30

Jon Elson elson at
Thu Dec 29 23:51:27 CST 2016

On 12/29/2016 10:04 PM, Noel Chiappa wrote:
>      > From: Cory Heisterkamp
>      > this is likely as close as I'll ever come to having a first generation
>      > machine
> Dude, as far as I'm concerned, if it uses some sort of circulating memory for
> main memory (either delay line or drum), it's pretty much first generation (of
> course, it all depends on how one defines generations).
> (Unlike the very similar - in size/cost/role - Bendix G-15, it doesn't have
> the 'next instruction' field in each instruction, to optimize performance,
> though...)
Ouch!  That means it runs one instruction per revolution of 
the drum?  that would slow it to something like 30 IPS!
> Interesting factoid about the Bendix G-15: it was designed with the help of
> one of the ACE people (Harry Huskey), and is basically a re-packaged ACE with
> drum instead of delay lines. There's an interesting article by Huskey himself
> in "Alan Turing's ACE" (by Jack Copeland) which discusses the G-15.
>      > From: William Degnan
>      > I am being very careful not to call this "the first personal computer"
> Oh, I think a good case can be made. People often cite the LINC as the first,
> but the G-15 and LGP-30 were similar in cost and intent, albeit a generation
> (at least) older.
SEVERAL generations older.  Core memory was a HUGE advance.  
Rather more complicated than a drum, but got rid of the 
horrid latency with a drum.  Even if you optimized the 
executable code, machines like the G-15 had all sorts of 
insane trickery to make data access faster.  There were 
instructions that would copy a whole long line of data to 
the short lines so that these could be accessed every 4 word 
times, instead of having to wait a full drum revolution for 
the next word.  There were all sorts of synchronization 
issues between where the instruction word was and where a 
data word was.  (Not meaning it would cause a failure, but a 
small program loop that was passing over a list of data 
words in a long line would be slowed to one loop per every 
few drum rotations, as the data access instruction would 
hang waiting on the data word to come around, then have to 
wait for the instruction word to come around, etc.) 
Programming the G-15 was massively arcane, with all sorts of 
side effects and especially tricks to improve performance, 
so your program would run in a day, instead of a couple 

Then, of course, The LINC was a discrete transistor machine, 
ran off a plain 120 V outlet, didn't require air 
conditioning beyond typical office environment, etc.  And, 
it had a CRT display that was used for OS interaction, 
program editing and viewing data.  That was also a big step up.


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