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Windows 7: Work out the true Megabytes for Gigabytes.

08 Sep 2017   #1
Paul Black

7 HP SP1 64-bit Vista HB SP2 32-bit Linux Mint 18.3
Work out the true Megabytes for Gigabytes.

Good afternoon,

I have seen several different explanations on how to work out a true 100 GB partition during a clean install for Windows 7 using Megabytes.
The calculation below seems to be the one recommended...

Perfect 100GB Drive = (10 x 10240) + (10 x 8) = 102480MB (Displayed as 100.00GB) this correct please?

I have used 102900 MB in the past but this appears as being greater than 100 GB.

Thanks in advance.

My System SpecsSystem Spec
08 Sep 2017   #2

W7 home premium 32bit/W7HP 64bit/w10 tp insider ring

Hi Paul,

thats the correct formula - MS justs like to be different

So 1029 would appear greater than 100.

Youll see a greater difference if you use an SSD
500GB converts down to about 490 usable

My System SpecsSystem Spec
08 Sep 2017   #3

Windows 7 Ultimate x64

Confusion on this matter comes all the time (there are many posts on the forum about this) and the answer it's always the very same: Microsoft got it wrong from day 1 and there is a (minor) bug in Windows that still exists.

Problem is that Windows displays decimal sufixes everywhere (kilobytes, megabytes, gigabytes, etc.) that imply multiplyng by 1000, but does the math for them in binary units (kibibytes, mebibytes, gibibytes, etc.) that multiply by 1024, hence there is a small difference in each and every size calculation.

The correct calculation is 100 x 1024 = 102400 MiB, but Windows will wrongly show 100.00 GB (when it should show 100.00 GiB), the bug is that it displays the wrong unit, but the calculation will still be correct.

I don't get why you added 10x8 thing, that will add a bit over 100GiB, but being so small it will be rounded. Also 102900 is somewhat bigger and might show a very small difference.

Anyway, may I ask why it's important to have an exact size?
My System SpecsSystem Spec

08 Sep 2017   #4
Paul Black

7 HP SP1 64-bit Vista HB SP2 32-bit Linux Mint 18.3


Thanks Roy, it is appreciated.


Anyway, may I ask why it's important to have an exact size?
When I do things I like them to be exact and correct. If I want a partition to be 100 GB I don't want it to be just over or just under what I have specified. No more than that really. I am probably being a bit anal about this but there is a LOT of discussions on the net trying to get to a difinitive answer to this question.

Thank you both for your answers.
My System SpecsSystem Spec
08 Sep 2017   #5

Windows 7 Pro 64 bit

Be aware that there is some rounding in drive specifications. Drives are not manufactured to have exactly the advertised capacity. The actual capacity will be somewhat more or less. Two drives from the same manufacturer with identical published specs may have been manufactured in different countries with significant internal differences, and with different capacities. It appears that this is particularly common with some removable devices.
My System SpecsSystem Spec
08 Sep 2017   #6

W10 Pro desktop, W10 laptop, W10 laptop, W10 Pro tablet (all 64-bit)

Other than your OCD tendencies, what does having a partition that "reports" it's size as exactly 100GB buy you? There is absolutely no benefit or consequence to being slightly more or slightly less. There's no way you could use exactly 100GB of disk space anyway.
My System SpecsSystem Spec
08 Sep 2017   #7

Win-7-Pro64bit 7-H-Prem-64bit

I too go for whole #gb's it makes it quite easy to align ssd's plus it just looks better
Although I use this which does have a portable you can install on a cd,
Best Free Partition Manager for Windows | MiniTool Partition Free
My System SpecsSystem Spec

 Work out the true Megabytes for Gigabytes.

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