[time-nuts] Drifting OT: Magic numbers in computers

David Forbes dforbes at dakotacom.net
Sun Jul 3 19:42:46 EDT 2005

At 3:39 PM -0700 7/3/05, Tom Van Baak wrote:
>Since I see you're also a fan of the intersection
>of precise time and prime numbers, have a look
>at one of my favorite articles on the subject:
>A Tutorial on Magic Numbers for High Definition Electronic Production

 From the article:

The FCC leaves a heritage of magic numbers: 7, 11 and 13, the factors 
of 1001. The mystical - some say unlucky - properties of these 
particular numbers were well known in ancient times.

An amusing if off-topic use of the magic primes is in the IBM 8" 
floppy disk. The original format was 77 tracks of 26 sectors of 128 
bytes each.

That is 2 * 7 * 11 * 13 = 2002 sectors.

The number of cards in a standard box of IBM punch cards was 2000. 
Coincidence? Of course not. The goal of the floppy disk project was 
to replace a box of punch cards with a single floppy disk, and the 
engineers went out of their way to achieve exactly that. Except they 
gave you two extra cards for free.


--David Forbes, Tucson, AZ

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