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I have a SSD with a capacity of 447 GiB. There are 319GiB used for files visible in Windows Explorer. The used space of the partition is reported by Windows as 393 GiB. This drive is only used for games, it has never contained an OS.

Running chkdsk it reports that

468718591 KB total disk space

415493328 KB in 64379 files

I am running a new instance of Windows 10 Pro with no changes to any default settings. The SSD was used with previous installations of Windows so I suspect that there are old system files which my current Windows instance won't show me.

The files take up 314 GiB but 393 GiB have been used. What could be taking up 74 GiB of space which isn't visible in Windows Explorer on a new vanilla Windows installation?

EDIT 1:

The disk contains a single partition which is 447 GiB as reported by Disk Management in Windows.

It appears that the partition is allocated the right amount, and that the free space Windows Explorer reports matches what chkdsk reports. The 15% discrepancy is between the size of visible files in Windows Explorer and size of files reported by chkdsk.

EDIT 2:

The space used by the visible files in Windows Explorer is 343,374,991,368 bytes. The space used by all files as calculated in chkdsk and the drive properties in Windows is 423,015,841,792 bytes. A difference of approximately equal to 73 GiB. The missing 73 GiB is not counting in 1000 vs 1024 as it is present when counting only in bytes.

EDIT 3:

Within the partition was a set of old system files from a previous installation of Windows. When viewed through Explorer they had a size of 0 B but Tree Size Free revealed had large file size.

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Flash_Steel
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  • It can be for various reasons such as file allocation unit size set when formatting the drive. – Chris Rogers Feb 16 '19 at 08:31
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    Plus, drive space is reported in Windows under [JEDEC memory standards](https://en.wikipedia.org/wiki/JEDEC_memory_standards), so space is in GB (Gigabytes which is 1024MB per GB) not GiB (Gibibytes) – Chris Rogers Feb 16 '19 at 08:43
  • How is the disk partitioned? Could it contain a recovery partition for a previous install? – davidgo Feb 16 '19 at 08:56
  • @ChrisRogers - I usually expect that there would be some small discrepancy, but 15% of the entire partition seems a huge amount. Also, I believe that JEDEC acknowledge their binary Mega is equal to Mebi rather than different to it, https://www.jedec.org/standards-documents/dictionary/terms/mega-m-prefix-units-semiconductor-storage-capacity – Flash_Steel Feb 16 '19 at 09:58
  • @davidgo - It is all in a single partition and I have edited my question to reflect this. – Flash_Steel Feb 16 '19 at 10:01
  • please show some screenshots to make it clear. Possible duplicate of [Why don't the sizes of my folders add up to the size of my hard drive in Windows?](https://superuser.com/q/304474/241386), [C: drive is full, but folders don't add up](https://superuser.com/q/455689/241386), [Why is the folder size (in properties) different from the total file/folder sizes in the folder?](https://superuser.com/q/567175/241386)... – phuclv Feb 16 '19 at 10:42

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You will be able to view every single directory and file if you select both "show hidden files" and "show hidden system files" in Folder Options, as shown in the following image. These two settings are both set to "don't show" by default on a vanilla Windows installation (at least since Windows XP).

dialog

It's likely there are hidden system files (with attribute S) in the partition, like Page File or whatever other programs have made hidden. Also, take into account that the Recycle Bin is hidden by default $RECYCLE.BIN.

iBug
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  • Good thinking. I had indeed forgotten to check the option for protected operating system files. Alas, this was not this issue. I unchecked the box and the same discrepancy was still present. – Flash_Steel Feb 16 '19 at 10:33
  • @Flash_Steel Have you re-calculated the file size? It's likely after unchecking them, the hidden files will show up and will add to the total size. You can alternatively just check if the size of the hidden files adds up to that very 73 GiB. – iBug Feb 16 '19 at 10:34
  • Yes, I recalculated viewing Hidden Files and Operating System Files. There was around 1 KiB in difference. I had just run Disk Cleanup on the drive before posting the question so that may have cleared out some of the files that would have been revealed. – Flash_Steel Feb 16 '19 at 10:38
  • @Flash_Steel As you said - there was a previous Windows installation on that volume - there certainly are paths that you can't access (guarded by ACL), for example, `\PerfLogs` or `\Windows\System32\Config`. You need some tweaks to actually see all files. – iBug Feb 16 '19 at 11:00
  • It was very weird. I could view the files in Windows Explorer but their file size was 0 Bytes. Obvioulsy Windows and chkdsk could see file sizes. Tree Size Free showed that they in fact had substantial non-zero sizes! – Flash_Steel Feb 16 '19 at 11:03
  • @Flash_Steel It's because when reading the occupation of a **volume**, there is no need to access individual files and sum them up, thus bypassing the ACL when counting sized. With your "total size of files" method, individual files *must* be accessible before their sized could be counted. This is probably the cause, AFAICT. – iBug Feb 16 '19 at 11:05