Re: Hashtable ordering
John B. Matthews wrote:
In article <c07g95til65tgpr8lmcgrif9b1d6ho8dum@4ax.com>,
Roedy Green <see_website@mindprod.com.invalid> wrote:
[...]
There was also the NCR CRAM. It consisted of a stack of magnetic
cards with rods running through the stack.
Featured here:
<http://www.computerhistory.org/brochures/companies.php
?alpha=m-p&company=com-42bc20992be7c>
Somehow the rods caused one of the cards to fall, and be sucked
around to be read, then replaced on the stack. It has been so long I
have forgotten precisely how it worked.
It looks like the notches represent a binary code. Shifting rods
laterally in the same pattern would release one card. I imagine using a
Gray binary code, or some other single-distance code, would reduce
jamming.
<http://en.wikipedia.org/wiki/Gray_code>
I don't think that would have been practical. When a card was released
from the drum, it always returned to the same end of the deck, so the
deck would be in last use order. The main attraction compared to
magnetic tape was random access to the cards, so last use order was
likely to be different from card number order.
I am an earwitness to the fact that whatever precautions were taken
against double drops were not totally effective.
Patricia