Apropos the use of SI prefixes and the prefixes for binary multiples, this is
the type of confusion we hope will someday resolve itself, now that a
standard set of prefixes for binary multiples is available. The quote below
comes from Plextor, makers of optical drives. See:
http://www.plextor.com/english/support/faqs/G00051.htm
I came across this while shopping for a DVD burner. Note that they do not take
their answer to the next level --- 10^9 versus 2^30. It is unclear to me
whether Microsoft et alia consider a "gigabyte" to be 1024^3 bytes or
1000x1024^2 bytes. In the case of 90 mm floppy disks, Microsoft considered a
"megabyte" to be 1000x1024 bytes!
Jim
[quote, edited by me to include missing carets]
Article ID. G00051
Why do I only get about 4.38GB on a DVD disc instead of the 4.7GB advertised
by the vendor?
DVD media has the same capacity conversion confusion suffered by users trying
to find out the correct capacity of their hard drives. Vendors compute
storage size in a decimal value, while computers compute storage in a binary
value. One megabyte (MB) of hard drive storage is computed by the vendor as 1
x 10^6, or 1,000,000. Computers are binary systems, seeing a megabyte as 1 x
2^20, or 1,048,576 bytes.
In a CD or DVD, a percentage of the disc is taken up by overhead, i;e. link
blocks, track information, reserved areas for video title, etc., and takes up
some of the user data area , but may not be part of the output data stream.
In the case of a DVD, this is approximately 1 MB.
So a DVD disc advertised by the vendor as 4.7GB (decimal) is displayed by
computer applications as approximately 4.38GB: (4,700,000,000 � 1,048,576) -
1MB = 4.38GB.
[end quote]
--
James R. Frysinger
Lifetime Certified Advanced Metrication Specialist
Senior Member, IEEE
http://www.cofc.edu/~frysingj
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