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I've just done an upgrade from Windows Vista Home to Windows 7 Home. I had previously done a backup of all the files i needed to keep ( pics, music, emails,...) on another computer.

In all, the backup files amount to about 50GB. The computer in question has a 160GB hd, but for some reason, Win 7 only sees it as having 136GB. I know the actual size of a disk is smaller than the spec, but by this much? Doesn't sound right to me...

Space was not an issue while it was running Vista.

Any ideas? Thanks!

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3 Answers 3

The difference will be decimal GB versus binary GB and file system formatting/overhead. HDD manufacturers always quote sizes in decimal units.

1 GB (decimal) = 1,000,000,000

1 GiB (binary) = 1024 * 1024 * 1024 = 1,073,741,824

So, 160,000,000,000 / 1,073,741,824 = 149,011,611,938.

The difference between 136 GiB and 149 GiB is probably the file system overhead plus the installation size for W7 - doesn't seem unreasonable.

Remember too that the size that the files require on disk is greater than their total size in bytes due to disk allocation units; each file is rounded up to the DAU.

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If the backed up docs only use around 50GB, then we have to assume that the OS is using the rest? I haven't installed any big software yet either... Win 7 can't possibly be using 90GB? –  Logikdev Feb 11 '10 at 8:26
    
@Logikdev: Do you have a typo in your question? I make 160 - 136 = 24, not 140+? –  Lawrence Dol Feb 11 '10 at 8:40
    
My Vista C:\Windows directory takes about 16 GiB. –  Lawrence Dol Feb 11 '10 at 8:42

You'll find at the "Engineering Windows 7" blog a nice article describing their effort regarding Disk Space.

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Actually just found out what's going on.

When installing Windows 7 as an upgrade, it keeps the old OS on the hdd in the windows.old folder. This folder used up 75GB in my case.

Here's the way to get rid of this folder:

Removing windows.old folder

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