spc3r21c.pdf tupo kib != KiB

Robert Snively rsnively at Brocade.COM
Fri Jan 21 09:28:52 PST 2005

* From the T10 Reflector (t10 at t10.org), posted by:
* "Robert Snively" <rsnively at Brocade.COM>
This is all good and constructive (and accurate) information.

The real key is that the units, whichever they are, should be
correctly specified in any documentation.  It really doesn't 
matter quite so much which you use, but proper specification
is a key.

As an example, as a marketing person, it would be in my interest to
use MegaBytes, because I can specify a number that is bigger
and because most people are more familiar with decimal arithmetic.

As a computer person involved in hardware and software design,
it would be in my interest to use MegaBytesBinary, because that is the 
arithmetic value most convenient to computer implementations.

In a standard, it is even more key that units be properly specified
using abbreviations and names that are internationally recognized.
However, a value or parameter could constructively be of either
decimal or binary type, depending on whether it is principally 
being made available for human/marketing use or for 
engineering/computation use.

That aligns with our discussion at the T10 meeting where
you chose and we agreed to accept familiar decimal percentage
numbers for health and free-space values, since those values
were principally focused on supporting human-useable interfaces.
Of course that may slightly complicate the programming in a
USB disk chip, since conversions from the actual fractional
value seen by the hardware, probably a binary fraction, to 
the desired decimal fraction would be required.  


> -----Original Message-----
> From: owner-t10 at t10.org [mailto:owner-t10 at t10.org]On Behalf Of Pat
> LaVarre
> Sent: Thursday, January 20, 2005 1:40 PM
> To: t10 at t10.org
> Subject: RE: spc3r21c.pdf tupo kib != KiB
> * From the T10 Reflector (t10 at t10.org), posted by:
> * "Pat LaVarre" <plavarre at lexarmedia.com>
> *
> "Standard" usage is split.
> The device folk who actually pay to create the storage build their
> companies on the physics of recording, be that flash, battery backup,
> rotating magnetic, whatever.
> Those physicists, like http://physics.nist.gov/cuu/Units/binary.html
> now, have consistently defined T G M K defined to mean 10 
> raised to the
> powers 12 9 6 3 since the metric era dawned, circa Bastille day 1789,
> drawing its prefixes from Greek teras, Latin gigas, Greek mega, Greek
> khiloi, etc.
> Yes the vast majority of people involved are the customers who buy the
> storage, and many of whom still speak of inches and ounces.
> Yes the physicists would be unemployed, without the 
> cooperation of those
> customers.
> Yes those customers have consistently defined T G M K in computing to
> mean 2 raised to the powers 40 30 20 10, denoted instead as 
> Ti Gi Mi Ki
> by the physicists of the U.S. NIST but then also the international IEC
> in December 1998, together with the pun of "mebibytes" pronounced like
> "may be bytes".
> But the physicists since the beginning have noticed that yielding in
> this dispute would mean they lose 2.4%, compounded with every
> generation.  To let T mean Ti costs 1.024 to the fourth power, i.e.,
> more than 9.95%, i.e., fuggeddaboutit.
> Our RAM colleagues could take a share of the blame here: in the
> beginning, they sold RAM architected to end on boundaries that grew
> exponentially as a power of two, without leaving room for ECC 
> and other
> overhead, as if physical storage were reliable.
> I remember in 2004 some friends & I checked a small 
> indeterminate sample
> of flash - I can report that least those flash folk had begun trending
> towards the physicists' T G M K, same as HDD always have.
> *
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