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Re: dd (coreutils) 5.97 used power of 10 not 2 for calculating MB

From: Pádraig Brady
Subject: Re: dd (coreutils) 5.97 used power of 10 not 2 for calculating MB
Date: Tue, 23 Jan 2007 10:16:25 +0000
User-agent: Thunderbird (X11/20061116)

Paul Eggert wrote:
> "Dat Head" <address@hidden> writes:
>> dd if=/dev/zero of=/dev/null count=100 bs=1024k
>> 100+0 records in
>> 100+0 records out
>> 104857600 bytes (105 MB) copied, 0.00933139 seconds, 11.2 GB/s
>> ---------------------------^^^ should be 100 MB
> No, "MB" means megabytes (i.e., 10**6 bytes).  I guess you want
> mebibytes (i.e., 2**20 bytes), but the standard abbreviation for that
> is "MiB", not "MB".  See <http://physics.nist.gov/cuu/Units/binary.html>.
> It might be reasonable to add support for binary multiples to "dd",
> but for media the decimal numbers are probably more useful.  As you
> mentioned, most media are measured in decimal multiples nowadays.

There is support for binary multiples in dd,
as I've summarized in the help output from my truncate util¹

<size> is a number which may be optionally followed
by the following multiplicative suffixes:
  b              512
  KB            1000
  K             1024
  MB       1000*1000
  M        1024*1024
and so on for G, T, P, E, Z, Y

> My favorite was the old "1.44 MB" floppy, which contained 1.44 * 1024
> * 1000 bytes.  Almost anything is better than that sort of confusion!

cool! You learn something new everyday.


¹ http://www.pixelbeat.org/scripts/truncate

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