I Don't Understand HD Capacity Ratings

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There seems to be a significant difference in the capacity I thought I was buying versus the capacity my iPhone and iPad show. Specifically:
- iPhone was purchased as a 16GB device. If I go to Settings->General->About, the capacity is shown as only 12GB, with 6.6GB available
- iPad was purchased as a 32GB device. If I go to Settings->General->About, the capacity is shown as only 26.7GB, with 16.9GB available.

In contrast, my iMac capacity rating appears to be spot on. It was purchased as a 640GB device. If I 'Get Info' for this Macintosh HD running Yosemite, the capacity is shown as a 639GB device, with 612GB available.

So it appears that my iPhone and iPad did a little false advertising :Angry:, whereas my iMac was extremely accurate. I would appreciate it if someone can explain why the difference ratings.

Thanks in advance.
 

bobtomay

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Math - Base 2 vs Base 10 - you can google it for more.

https://support.apple.com/en-us/HT201402

......

Apple changed OS X to use Base 10 instead of Base 2 calculations a few years ago to stop this question - which frankly was being asked all the time - even here in this forum, we saw this question practically every day - sometimes multiple times a day. Apple should have done it with iOS at the same time.

OS X is, at this time, the only operating system that has been converted to use Base 10 while every drive manufacturer uses Base 10 in advertising their drive sizes.
That is why you will always see the 1 GB = 1,000,000,000 bytes on the packaging.
 
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Math - Base 2 vs Base 10

https://support.apple.com/en-us/HT201402

......

Apple changed OS X to use Base 10 instead of Base 2 calculations a few years ago to stop this question - which frankly was being asked all the time - even here in this forum, we saw this question practically every day - sometimes multiple times a day. Apple should have done it with iOS at the same time.

Thanks for the education. I do understand base 10 versus base 2, but I had no idea that Apple used different bases for their little iDevices. Since I bought the iMac first, I never expected different math on the products I later bought. My dumb mistake.

You sound a little perturbed that someone else has now asked the question you've faced multiple times a day. Sorry, but that happens sometimes on good forums with wide membership. I did do several unsuccessful searches of forum posts before I asked the question.

Thanks again for the info.......
 

bobtomay

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It's not a dumb question and it has been a long while I think since anyone asked about this here.
There were times in the past where a thread with this question could be seen 2-3 times in the first page of returns in the 'New Posts' link or 10+ times in the past week. Sorry, my frustration is not at all at you, but at Apple, for not making the same change across both of their operating systems.

Of course with Apple using Base 10 within the OS, am surprised we haven't seen the "Windows says this file is "X" size and OS X says it is "Y" size" questions.
 

Slydude

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I think if he's perturbed at anyone it's at Apple for not changing IOS to report things using the same base as OS X uses.
 

bobtomay

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And actually, the frustration belongs squarely on the shoulders of the drive manufacturers. Then again, they're behind the 8 ball. They're going to have to state what 1 GB equals no matter what they do. If they put "1 GB = 1,073,741,824 bytes" on the label, half the consumers would be doing a double take.
 

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For what it's worth. I have a 13" 2011 MacBook Pro with a 320gig hard drive. Doing a "Get Info" on the HD…it's capacity is listed as 319.21gig.

I'm not going to loose any sleep over 320gig vs. 319.21gig!;)

- Nick
 
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There seems to be a significant difference in the capacity I thought I was buying versus the capacity my iPhone and iPad show. Specifically:
- iPhone was purchased as a 16GB device. If I go to Settings->General->About, the capacity is shown as only 12GB, with 6.6GB available
- iPad was purchased as a 32GB device. If I go to Settings->General->About, the capacity is shown as only 26.7GB, with 16.9GB available.

In contrast, my iMac capacity rating appears to be spot on. It was purchased as a 640GB device. If I 'Get Info' for this Macintosh HD running Yosemite, the capacity is shown as a 639GB device, with 612GB available.

So it appears that my iPhone and iPad did a little false advertising :Angry:, whereas my iMac was extremely accurate. I would appreciate it if someone can explain why the difference ratings.

Hi Durango - yep, base 2 vs. base 10 makes a difference - on my 64 GB iPad Air 2 & wife's 64 GB iPhone 6, the total capacity reported in settings is 55.9 GB - now the 64 GB advertised is using base 10 (i.e. 64,000,000,000 bytes); BUT, 1 GB in base 2 = 1,073,741,824 bytes, so if my iDevices capacity is being stated in 'base 2 GBs', the 64 divided by 1.0737 equals 59.6 - I suspect that the discrepancy of about 4 GB is being used by the iOS. Dave :)
 

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