I couldn't say for sure, but in general, when you are talking about the speed of a line in kilobits per sec, megabits per sec, etc. Those lines are all measured in units of 1,000 (ie. a 64kbps circuit is
64,000 bits per sec, a 3mbps line is 3,000,000 bits per sec).
Almost everyone still refers to a Metabyte as 1048576 bytes, drive manufacturers and the mebibyte people withholding.
They probably are just going with the normal convention that most people use.
One thing to note is that Iperf uses 1024*1024 for Megabytes and 1000*1000 for Megabits.
Data formatting: (-f argument)
The -f argument can display the results in the desired format: bits(b), bytes(B), kilobits(k), kilobytes(K), megabits(m), megabytes(M), gigabits(g) or gigabytes(G).
Generally the bandwidth measures are displayed in bits (or Kilobits, etc ...) and an amount of data is displayed in bytes (or Kilobytes, etc ...).
As a reminder, 1 byte is equal to 8 bits and, in the computer science world, 1 kilo is equal to 1024 (2^10).
For example: 100'000'000 bytes is not equal to 100 Mbytes but to 100'000'000/1024/1024 = 95.37 Mbytes.
Well, since he's apparently benchmarking some device, it must mean he actually has something working. There's hope, methinks, maybe.
Perhaps it would be more appropriate to ask on the iPerf mailing list:
Oh, he already posted a question and got a mostly wrong answer. Oh well.
Pretend I didn't mention IEC 60027-2 A.2 which uses kibi, mebi, and gibi bytes.
However, he wanted to know why iPerf did it both ways. The first version of iPerf was scribbled in May 2001. The ISO released the binary prefix standards in 1998, which are generally ignored by the industry to this day. Until the failure to use kibi, mebi, and gibi bytes is made an international crime punishable by being forced to read the entire standard from cover to cover, the choice of prefixes are those of the author.
Really? I always thought that (in digital-land) since 1 Kbyte = 1024 bytes, a Mbyte is 1024*1024 = 1,048,576 bytes. And a Gbyte = 1024 (1k) mBytes =
1024^3 = 1,073,741,824 bytes. In other words, "digital" SI prefixes are a little bit larger than "engineering" ones, and conveniently follow power-of-two groupings (kilo=2^10, mega=2^20, giga=2^30, tera=2^40). Wikipedia seems to agree
formatting link
and further informs me that the NIST has created a new set of prefixes that follow this new digital meaning: "kibi" (for "kilobinary"), "mebi", etc.
The real reason for this difference, which for some reason is rarely given, is because of address decoding. If you have a RAM chip, the memory cells are addressed by a binary address, so this leads naturally to blocks of memory that are powers of 2. One could design RAM chips with 1000 byte blocks say, but it makes the address decoding unnecessarily complex. Binary addressing is the most efficient method.
For disk drives the magnetic recording medium is linear, so the block size and cylinder/head/sector addressing can be arbitrary and not based on powers of 2. For convenience, the sector size is chosen to be a power of 2 to match how memory is arranged. Whether the overall storage size of a disk is quoted in SI or K is down to preference, but the manufacturers prefer the standard SI units.
For communications, the bit rate is determined by a clock, which is also somewhat arbitrary and doesn't need to be based on powers of 2. Therefore it is natural to use the standard SI units.
So in general, SI units are the preferred units. For directly addressed RAM chips (or ROM, Flash etc) a binary unit reflects the underlying layout, and gives an integral value. For storage media like disks, it's a gray area, and usage depends on choice. For communications and bit rates, SI units are normally used. In all cases, I recommend to use the IEEE binary prefixes (KiB, MiB etc) where appropriate to make it clear which unit is being used.
And I think that the world would be a lot better off if most marketing types (along with a few other groups) suffered the fate of "The marketing division of the Sirius Cybernetics Corporation". :-)
I have enough trouble keeping people straight in conversation about the difference between MegaBytes and Megabits that the difference between 1024 and 1000 gets lost in the noise.
I have a nicely prepared document from a large firm last month that used MB throughout, and by knowing some of the background, I could tell that some were Megabits, and others MegaBytes, within the same page of text.
On all of the iperf tests, it would have been wise to specify the -f format, since the performance of my network, just to add to the misery, was often 1/10th of the speed of nominal, and the iperf output default would fluctuate, making careful attention to the labels important. That was occasionally overlooked.
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