
Printer's key - senorgusto
https://en.wikipedia.org/wiki/Printer%27s_key
======
jewel
In summary, what book printers used to do is have a line of numbers on the
title page of the book, which they would erase one at a time with each
printing run. The reason why is that they would be reusing the original plates
in the printing press, and it was easy to erase a number (by destructively
removing it from the plate) as opposed to recreating a whole new plate for the
title page.

Flash memory works in a similar way. After a block is erased, which is a slow
process, it starts with all ones. It's very fast to switch a cell from a 1 to
a 0, but to turn a 0 back into a 1 you have to erase the whole block again.
(Block sizes can vary considerably, as much as 512 KiB on SSDs.) Note that
it's the erase cycle which reduces the lifetime of the flash, not the switch
from a 1 to a 0.

USB flash devices and SSDs don't expose low-level access to the NAND flash so
it's not possible to take advantage of this property, but if you could you'd
be able to have a small counter with one bit per number. Perhaps in some
circumstances a bitmask would also work well. A bloom filter could also be
implemented efficiently this way.

I imagine that embedded programmers and the SSD firmware takes advantage of
this property of flash memory for its own data structures, I'd love to hear if
that's the case.

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LeoPanthera
Does that mean that it's better to securely erase flash disks with FF's rather
than 00's?

~~~
omgtehlion
There is no difference from security point of view. To erase SSD you just
TRIM[0] the whole device and wait some time while it erases underlying flash.

[0]
[https://en.wikipedia.org/wiki/Trim_(computing)](https://en.wikipedia.org/wiki/Trim_\(computing\))

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johnobrien1010
Other fun book facts: by looking at the length of the number that is the
second to last digit in the ISBN, you can tell how many large an ISBN block
the publisher bought, which often relates to the size of the publisher. If
it's only two digits, they only bought a block of 100 ISBN's, so they're
probably a very small publisher.
[https://en.wikipedia.org/wiki/International_Standard_Book_Nu...](https://en.wikipedia.org/wiki/International_Standard_Book_Number)

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marincounty
I was watching this tv show about Horder's. The older gentleman collected
books. His place needed some cleaning, but his domicile was definitely
livable, and didn't look like a health hazard.

Well, his well meaning kids, and Ph.D, along with the army of helpers barged
into his home, and gave dad the ultimatum, "Throw out this junk!". He caved in
--I think he was tired too? The only thing I really remember from the show was
one phrase from this man. He said, "But, a lot of these are first editions?".

The production crew seemed baffled when the dumpster filled with these books
would magically empty itself overnight. I recall them saying someting like,
'There's so many Horder's out there? What a travesty?". And the melodramatic
music played in the background.

I guess it resonated with me because I collect first edition books?

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GabrielF00
While we're on the subject, does anyone know why books don't usually start at
page one? Even in the case of a novel, where there's no preface in roman
numerals, the book will often start on page three or four.

~~~
svisser
Books tend to have blank pages at the beginning and/or end when the actual
number of pages isn't a multiple of, say, 8, 16 or 32.

[https://en.wikipedia.org/wiki/Intentionally_blank_page#Print...](https://en.wikipedia.org/wiki/Intentionally_blank_page#Print_media)

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atsaloli
Nice. Reminds me of the explanation why the code for DEL (delete) in ASCII is
127 (1111111) -- back in the days of punchcards, when a punched hole meant
"one" and no hole meant "zero", you could convert any other code into 1111111
by overstriking it (similar to how in the days of typewriters you could
overstrike any other letter with X to cross it out).

~~~
drfuchs
Close, but that only worked for punched paper tape (which had 7 positions for
hole / not-hole per row, with a direct mapping to ASCII). Punch cards used
Hollerith code, with 12 positions per column, with a peculiar mapping to
EBCDIC, where there would be only one hole in rows 1 to 8, which more or less
gave the bottom 3 bits of the character, and a combination of holes in the
other 4 rows, giving the other 4 bits.

~~~
atsaloli
Thank you!

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sowbug
If you find this interesting, you'll love
[http://www.linotypefilm.com/](http://www.linotypefilm.com/). It was on Amazon
Prime Video about a year ago.

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personjerry
Neat! Nice to see that there were hacky thinkers back in the day :)

