[ntp:questions] 500ppm - is it too small?

Uwe Klein uwe_klein_habertwedt at t-online.de
Thu Nov 12 14:34:26 UTC 2009


Joseph Gwinn wrote:
> In article <87r5s3syxz.fsf at pc9454.klinik.uni-regensburg.de>,
>  Ulrich Windl <Ulrich.Windl at RZ.Uni-Regensburg.DE> wrote:
> 
> 
>>"nemo_outis" <abc at xyz.com> writes:
>>
>>
>>>"Richard B. Gilbert" <rgilbert88 at comcast.net> wrote in
>>>news:TLSdnQ2E26bBLBnXnZ2dnUVZ_sydnZ2d at giganews.com: 
>>>
>>>
>>>>nemo_outis wrote:
>>>
>>>...
>>>
>>>>>I fail to see the value or relevance of "500ppm satisfies 98% of
>>>>>computer clocks" if some other number, perhaps 5000 ppm, could
>>>>>satisfy yet even more than 98% of computer clocks with no downside -
>>>>>as indeed seems to be the case!  Chrony, whatever its other merits
>>>>>and demerits, is an "existence proof" for this proposition.
>>>
>>>
>>>>I can't follow Dave's math but I'm reasonably sure that there is a
>>>>good reason for the 500 PPM limit.  Since almost all computer clocks
>>>>can meet this criterion I'm not going to worry about it.
>>>
>>>Hmm, "faith-based" ntp?  Not for me.  If there is a "good reason" I'd 
>>>like to hear it - 500 ppm has the smell of arbitrariness about it.
>>
>>As arbitrary as there are 8 bits in a byte.
> 
> 
> No, 8 bits isn't arbitrary.  
> 
> Computer hardware is simplified if the various word lengths are all 
> powers of two.
> 
> Eight bits was the smallest power-of-two size that allowed the full  
> Roman alphabet including punctuation and control characters to be coded.
> 
> There are 5, 6, and 7 bit codes, all now obsolete:
> 
> Five-bit: Baudot, used in teletypes.
> 
> Six-bit:  Fieldata (Univac and Control Data, and others I assume.)
> 
> Seven-bit:  ASCII without parity bit.
> 
> Eight bit:  ASCII with parity bit, and EBCDIC 
> (http://www.ncsa.illinois.edu/UserInfo/Resources/Hardware/IBMp690/IBM/usr
> /share/man/info/en_US/xlf/html/lr425.HTM)
> 
> ASCII came from AT&T, while EBCDIC came from IBM.
> 
> 
> And now sixteen bit: Unicode.  
> (http://unicode.org/standard/WhatIsUnicode.html)
there is 32bit unicode too.
The stream encoding is a variadic kommaless coding based on 8bit bytes (octets)

uwe




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