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

[cheater cheater]

Indeed, quite a bit of turmoil there - the NASA report was fairly scathing.

On Fri, Jan 18, 2013 at 9:43 AM, Paul Burns <paul at fitvideo.co.uk> wrote:
> 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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