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I am learning computer architecture and organization I am stuck in the following question.

Consider a hard disk with sector size 1024 bytes, 5000 tracks per surface, 64 sectors per track, and 8 surfaces. If the disk platter rotates at 10,000 rpm, and one track of data can be transferred per revolution, the average data transfer rate is ……………. Mbytes/sec.

Correct answer is 10.66 Mbytes/sec.
1 track = 64 x 1024 = 64 Kbytes.
Time for one revolution = 6 msec.
So, in 6 msec the data transferred is 64 Kbytes
Thus, in 1 sec the data transferred is 64 / 6 Mbytes = 10.6 Mbytes/sec

The solution was given along with the question which I think is wrong as the correct answer should be (64 * 1000) / (6 * 1024) = 10.41 Mbytes/sec.

SamGibson
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Anshul Gupta
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  • A drivemaker's guide on confusing people and padding metrics: use 1000 instead of 1024 from time to time. May drive makers never get into baking or the bakers' dozen will face greater danger... – Abel Apr 25 '21 at 17:07
  • what is the *1000* in your equation? – jsotola Apr 25 '21 at 17:21

1 Answers1

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The actual number is 10922666.6666667 bytes/second.

If you divide by 1024, you can write it as 10666.666 kbytes/second.

If you divide by 1024 again, you can write it as 10.416 Mbytes/second.

Apparently, whoever wrote the answer decided to take the middle figure and divide it by 1000 in order to call it "megabytes". This is just wrong.

Dave Tweed
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    This kind of confusion comes up a lot and even ended with a legal settlement between flash memory sellers and buyers. By international standard, 1000 bytes is **defined** as one kilobyte and 1,024 bytes is **defined** as one kibibyte, where "kibi" is supposed to mean something like a "binary kilo". Likewise, 1,000,000 bytes is a megabyte but 1,048,576 bytes is a mebibyte. – Elliot Alderson Apr 25 '21 at 17:49
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    @ElliotAlderson: Yes, but whoever wrote the answer used one factor of 1024 and one factor of 1000. That's why it's "just wrong". – Dave Tweed Apr 25 '21 at 21:29
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    You are absolutely right, the answer quoted by the OP is a hot mess. I was just trying to add some details to your correct answer. – Elliot Alderson Apr 25 '21 at 22:12