[NBLUG/talk] Good hardwar vendors (was Missing ReiserFS superblock!)

Ron Wickersham rjw at alembic.com
Tue Jul 25 14:42:59 PDT 2006


On Mon, 24 Jul 2006, Lincoln Peters wrote:

---snip---

> I do have one concern about this hard disk: one reviewer on NewEgg
> said that the 500GB are "salesman's" gigabytes, meaning 1,000,000,000
> bytes instead of 1,073,741,824 bytes.  That means that the size is
> actually about 465GB!

the confusion is the result of the practice of "adopting" the SI
prefixes for powers of ten and changing them for nearby powers of
two.  this was primarily done for memory since devices were addressed
in powers of two, but was also used in other quantities and it was
necessary to guess the context and sort of know what units were actually
being discussed.

because the practice was widespread, yet clearly a corruption of the
international standard of units (SI), in 1998 the IEC ratified new units
for powers of two.  these units spelled out include bi for "binary" in
the prefix so 2^10 is kibi, 2^20 is mebi, and 2^30 in gibi.   the
symbols are Ki, Mi, and Gi respectively.

so in base 10
kibibyte (KiB) is         1,024 bytes
mebibyte (MiB) is     1,048,576 bytes
gibibyte (GiB) is 1,073,741,824 bytes

while
kilobyte (kB) is         1,000 bytes
megabyte (MB) is     1,000,000 bytes
gigabyte (GB) is 1,000,000,000 bytes

note that the units begin in lower case while the symbols are upper case
(along with all units bigger than 10^0 or 2^0) with the exception of kilo
whose symbol is lower-case k (since K is reserved for Kelvin).

the IEEE suggests we pronounce bi as "bee" in english speech.

since disk storage decended from punch cards and paper tape and later
storage drums the practice of stating capacity in base 10 predates the
usage of the word byte (as does communication speeds which are also in
base 10).

for a truly wierd combination of units, the "1.44MB" diskette is neither
1.44 in decimal or binary...and is 1000 kibibytes.   so that makes it
1.475 MB or 1.406 MiB.  and Seagate defines gigabytes as 1,024,000,000
bytes while other drive manufactures use 1,000,000,000.

CD capacity is always in binary units "770MB CD" is 770 MiB.
DVD capacity is always in decimal units "4.7GB DVD" 4.75 GB or 4.38 GiB.

-ron



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