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| 7/13 |
| 2005/2/3-5 [Computer/HW/Memory, Computer/HW/Drives] UID:36055 Activity:moderate |
2/3 So, I'm really confused about this notion of computer science
metrics where everything's kind of 2^n, but sometimes not. For
example, if I have a 4 GIG hard drive, does that mean I have
exactly 2^32 bytes of space? Does that translate to 4000000000
bytes, or some number that's close to it? How about megahertz?
Say I have a 2.5GHz computer, does it run at exactly 2500000
hertz? Or 2^n for some multiple of n?
\_ As a few other people have said, just about everything is ordinary
decimal units now. A 4G hard drive is (about) 4,000,000,000 bytes,
and a 2.5GHz processor runs at (about) 2,500,000,000 Hertz.
Operating systems still tend to report file sizes in binary units,
though, so a 4G file is probably 4,294,967,296 bytes. (Sometimes
it's configurable: GNU du and df let you specify -h for binary
units or -H for decimal.) The only hardware still sold in binary
units is memory -- a 1G flash memory card is 1,073,741,824 bytes.
Also note that all storage devices are sold by raw capacity, not
counting filesystem overhead.
\_ I'd actually argue that in computers, all standards and measurements
are 10^n with the exception of RAM and addresses. HDDs, bandwidth,
frequency, resolution (megapixels) are all base ten.
\_ The ISO standard (IIRC) is Gibibytes for 2^30 and Gigabytes for
10^9. Memory is addressed by logic which is friendly to powers of
2. Non-memory doesn't matter.
\_ Frequencies (Hertz) are not stated in powers of two obviously.
You can usually find the exact frequency in the tech specs.
Computer data quantities are normally referred to with binary
prefixes (kilo=1024). Hard drive producers use 1000 because
they are fuckers. A frequency is not a data quantity.
\_ The whole k=1024 thing was a cute hack invented by computer
folks, but it becomes imcreasingly strained as you move into
mega- and giga- prefixes. At some point you need to admit it's
more trouble than it's worth. The computer should be the one
worrying how to address it's memory in base-2, rather than the
end user wondering how many bytes are in a gig.
\_ Memory is sized in 2^n because that's how the chips are laid out.
The capacity of a hard drive is determined by the track width
and magnetic domain size. This gives you a non-binary capacity.
It makes sense to therefore measure it using the SI system. The
fact that CS people started calling 1024 and 1048576 kilo- and
mega- when those prefixes had been in use for ages says to me
that the CS people are the fuckers, not the engineers who are
just adhereing to standard terminology. I personally count all
file and data sizes in base-10, except when refering to memory
usage. Anyway, this debate has been done to death before.
\_ so 1M is what really? 1000000 or 10^20?
\_ Officially, 10^6 (you mean 2^20, right?).
M = 10^6, Mi = 2^20
See:
http://physics.nist.gov/cuu/Units/binary.html
\_ No, it doesn't make sense when you're talking about computer
storage capacity to use a different meaning of GB than
everybody normally uses when talking about computer storage.
It's not like the drives are storing non-binary data. It's
going to have a filesystem and store vanilla kilobytes and
megabytes. Nowhere else does Gbyte refer to 1000*1000*1000.
In a computer environment, files are loaded into memory and
to disk, it's idiotic to change the terminology just because
the underlying media is different. CD and DVD storage is
referred to in binary. Sorry, you're wrong.
\_ FWIW, floppies are counted under a bastardized hybrid
system where 1.44 'megabytes' = 1440 KiB, or 1.44k-KiB
\_ No. CDs and DVDs are counted base-10, as is bandwidth.
The fact that the drives are storing binary data has no
bearing on the method you use to count the bytes, which
this debate shows, is a matter of dueling conventions, not
some underlying fact. I'm not wrong, you're just an ass.
\_ The orange book standard says a cd has a capacity
of 650*2^20 bytes.
\_ A DVD+-R(W) is 4.7*10^9
\_ Hard to argue, since they charge $5,000 for a
copy of a DVD format spec ($500 for each
additional spec) and require an NDA. Do you
actually have access to the four specs you
mention? The holder of DVD Forum's specs is
http://www.dvdfllc.co.jp |
| 7/13 |
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| physics.nist.gov/cuu/Units/binary.html home page Prefixes for binary multiples In December 1998 the International Electrotechnical Commission (IEC), the leading international organization for worldwide standardization in ele ctrotechnology, approved as an IEC International Standard names and symb ols for prefixes for binary multiples for use in the fields of data proc essing and data transmission. It is important to recognize that the new prefixes for binary multiples a re not part of the International System of Units (SI), the modern metric system. However, for ease of understanding and recall, they were derive d from the SI prefixes for positive powers of ten. As can be seen from t he above table, the name of each new prefix is derived from the name of the corresponding SI prefix by retaining the first two letters of the na me of the SI prefix and adding the letters "bi," which recalls the word "binary." Similarly, the symbol of each new prefix is derived from the s ymbol of the corresponding SI prefix by adding the letter "i," which aga in recalls the word "binary." The full content of Amend ment 2, which has a publication date of 1999-01, is reflected in the tab les above and the suggestion regarding pronunciation. Subsequently the c ontents of this Amendment were incorportated in the second edition of IE C 60027-2, which has a publication date of 2000-11 (the first edition wa s published in 1972). The complete citation for this revised standard is IEC 60027-2, Second edition, 2000-11, Letter symbols to be used in elec trical technology - Part 2: Telecommunications and electronics. Historical context^* Once upon a time, computer professionals noticed that 2^10 was very nearl y equal to 1000 and started using the SI prefix "kilo" to mean 1024. Tha t worked well enough for a decade or two because everybody who talked ki lobytes knew that the term implied 1024 bytes. But, almost overnight a m uch more numerous "everybody" bought computers, and the trade computer p rofessionals needed to talk to physicists and engineers and even to ordi nary people, most of whom know that a kilometer is 1000 meters and a kil ogram is 1000 grams. Then data storage for gigabytes, and even terabytes, became practical, an d the storage devices were not constructed on binary trees, which meant that, for many practical purposes, binary arithmetic was less convenient than decimal arithmetic. The result is that today "everybody" does not "know" what a megabyte is. When discussing computer memory, most manufac turers use megabyte to mean 2^20 = 1 048 576 bytes, but the manufacturer s of computer storage devices usually use the term to mean 1 000 000 byt es. Some designers of local area networks have used megabit per second t o mean 1 048 576 bit/s, but all telecommunications engineers use it to m ean 10^6 bit/s. The confusion is real, as is the potential for incompatibility in standards and in implemented sy stems. Faced with this reality, the IEEE Standards Board decided that IEEE stand ards will use the conventional, internationally adopted, definitions of the SI prefixes. Mega will mean 1 000 000, except that the base-two defi nition may be used (if such usage is explicitly pointed out on a case-by -case basis) until such time that prefixes for binary multiples are adop ted by an appropriate standards body. SI prefixes *Historical context adapted from: Bruce Barrow, "A Lesson in Megabytes," IEEE Standards Bearer, January 1997, page 5 Portions copyright 1997 b y the Institute of Electrical and Electronics Engineers, Inc. The IEEE d isclaims any responsibility or liability resulting from the placement an d use in the described manner. Information is reprinted with the permiss ion of the IEEE. |
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