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Error in test

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There is a question - How many bits are in megabit? With proposed answer 1048576. It is wrong.

Megabit contains 1000000 bits.

1048576 bits are in mebibit.

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You just took a course or a lecture?   :drool:


1mega is 1 million, so yes, 1Mb = 1,000,000 bits. Officially... And the same applies to MegaBytes of course!


Now, the Kb, Mb, Gb to Tb notations are mostly used in relation to bit rates which, as far as I can recall, were most commonly calculated in powers of 10, i.e. 10n. For instance, when I started working as a network engineer in the '90s, 1Kb/s or 1Kbps = 1000bps, not 1024bps. When we deployed leased lines of say 128k, 256k or 1M, in the Telecom world it always meant 128,000bps, 256,000bps or 1,000,000bps.


It's for volume such as file size that that things (used to?) differ with the use of the byte (8bits or octet) notation. KB/MB/GB/etc. were calculated in powers of 2, i.e. 2n. As such:

  • 1KB = 210 bytes, i.e. 1,024 bytes
  • 1MB = 220 bytes, i.e. 1,024 kB or 1,024 x 1,024 = 1,048,576 bytes or 1,048,576 x 8 = 8,388,608 bits
  • 1GB = 230 bytes, i.e. 1,024 MB = 1,024 x 1,024 x 1,024 =  1,073,741,824 bytes
  • 1TB = 240 bytes, i.e. 1,024 GB =  1,024 x 1,024, x 1,024 x 1,024 = 1,099,511,627,776
  • and so on...

I can't recall my entire computing history but this derived from the fact that with n bits, you get 2n different values. 210 gives up to 1,024 values which was the closest to 1,000. And that's how the computing binary kilo came out to begin with. Please note that this notation remains heavily used in the computing world to date.


Since end 1998, the official IEC organisation has based things on the regular metric international standard (SI) of powers of 10, i.e.

  • 1kB = 1,000 bytes
  • 1MB = 1,000,000 bytes
  • 1GB = 1,000,000,000 bytes
  • 1TB = 1,000,000,000,000 bytes
  • and so on...


Indeed, the "old" computing-world notations for powers of 2 now officially uses the following convention:

  • kibi = kilo binary
  • mebi = mega binary
  • gibi = giga binary
  • tebi = tera binary
  • and so on...

but you'll hardly ever see those mentioned. For a huge number of people, the original notations most probably prevails. Rightly or wrongly, not for me to say...


Question is (and without checking 1st): which convention does macOS use? Which one does Win10 use?  ^_^

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You just took a course or a lecture?   :drool:

I just took a new member test, to be allowed to participate in this forum. This test contained a question about bits in megabit, with 3 invalid answers offered.

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I guess these were written by old farts (like me) for whom 1KB will always be 1024bytes. In fact, JEDEC still refer to the old computing norm for memory (RAM), i.e. 1KB=1024bytes.




Whether the answers you got are invalid or not will remain an open debate, I guess. And i2=-1 afterall...

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