[sdiy] Cray history, was: Static ADC and DAC recommendations?

[Paul Burns]

Hi there , he may well have to do a lot of explaining , as he did in this
missive from a guy who went on to be communications CEO of NASA.

http://www.mediafire.com/view/?3olonbu1tq02mft

regards

Paul
-----Original Message-----
From: cheater cheater [mailto:cheater00 at gmail.com] 
Sent: 17 January 2013 23:40
To: Paul Burns
Cc: Phillip Harbison; sdiy diy
Subject: Re: [sdiy] Cray history, was: Static ADC and DAC recommendations?

I read at some point Cray got so pissed off with the way things were going
(as influenced by management) that he shut down his whole lab, built a
factory hall 250 km away, and only started after all the technical workers
moved there :) Management wasn't allowed :) But apparently after he was let
off the leash he couldn't deliver, and after being put on the back burner
left the company. Read all about
it:
http://en.wikipedia.org/wiki/Seymour_Cray#CDC.27s_Chippewa_Falls_laboratory

Then, your uncle had to explain why CDC wasn't doing so well, especially
compared to IBM:

http://tinyurl.com/ax8udh5

(full url:
http://books.google.de/books?id=khwnFtEzTccC&pg=PA45&lpg=PA45&dq=john+w+lace
y+cdc&source=bl&ots=Rk6pnA5tjo&sig=6FlpRZXxDpAUhbuHVm_mowMSxbM&hl=en&sa=X&ei
=nYj4UJ7ZI8aQ4gTBs4DgDA&ved=0CCoQ6AEwAA#v=onepage&q=john%20w%20lacey%20cdc&f
=false
)

interestingly enough it's the first link that shows up if you search for his
name and "CDC"..

Cheers

On Thu, Jan 17, 2013 at 11:54 PM, Paul Burns <paul at fitvideo.co.uk> wrote:
> Thank you for the historical insight, my uncle is one John W. Lacey 
> who was a top dog at CDC right from the outset ( he used to employ 
> Seymour Cray ;-)
> )
> Regards
> Paul Burns.
>
>
> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Phillip 
> Harbison
> Sent: 17 January 2013 22:41
> To: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] Static ADC and DAC recommendations?
>
> cheater cheater wrote:
>> Wait a sec guys - I thought the usual approach was folding converters.
>> That is, you take the input signal, scale it to e.g. 0-1V, and see if 
>> it's the upper or lower half [...]
>
> That essentially describes one type of ADC, the successive 
> approximation variety. The other type is a flash converter, where you 
> have enough comparators on the chip to do this all in parallel. The 
> problem is flash converters obviously get exponentially complex as you
increase the accuracy.
> You'll need twice as many comparators to go from 4 bits to 5 bits, so 
> anything beyond about 8 bits is prohibitive, and I've only seen it 
> used in extreme applications like video ADCs where 8 bits per color is 
> usually sufficient.
>
> Another problem is even with a flash ADC, you'll need some settling 
> time so there's still the issue of delay time even if you don't consider
it clocked.
> I don't think a continuous output is possible or at least not 
> realistic. I second the suggestion of using a sample rate high enough 
> that you don't notice it is not continuous. An ADC capable of 200K 
> samples per second should be good enough for audio.
>
> If you really need continuous signal processing, that is why we still 
> have analog computers. In my younger days I had the opportunity to 
> visit the McMorrow Labs, a research center on Redstone Arsenal 
> (Huntsville, AL) that does simulations to test missile guidance 
> systems. I was majoring in computer engineering so this was quite a 
> thrill. They had a CDC-7600 which was the fast supercomputer in those days
(the Cray-1 was not yet shipping).
> Connected to the 7600 was a CDC-6600 which interfaced to a room of 
> analog computers about the size of a hockey rink. I would guess there 
> were about
> 200 to 300 analog computers each about the size to two 19" x 84" racks.
> I asked why they needed all these analog computers, which I considered 
> to be fossils, when they had the fastest computer in the world 
> downstairs. My guide explained that solving any one of these complex 
> differential equations, each of which was handled by an analog 
> computer, would bring that
> 7600 to its knees. The analog computers were the right tool for the 
> job. The
> 7600 ran a Fortran program that read descriptions of differential 
> equations to patch layouts for the analog computers. OK, it did a few 
> other things. :)
>
> "If the only tool you have is a hammer, every problem looks like a 
> nail." -- me
>
> --
> Phil Harbison
>
>
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