Used Space on C vs Size on Disk of Folders/files on C

[Alan C. Brown]

I have just re-installed WinXP Pro SP2 from a Toshiba Recovery CD and
updated to XP Pro SP3 on my Toshiba Satellite Pro M70 laptop.

When I click My Computer it shows :

Local Disk C:
Toal Size - 19.9 GB
Free Space - 10.2 GB

Used Space - 9.70 GB

However when I right click on Local Disk C: & select explore, and then
highlight all the folders in the right pane of Windows expoler,and click on
properties, the info I get is :

44,671 Files, 2630 folders
Sze: 6.14GB
Size on disk: 6.04GB

Therefore there is a difference of 3.66GB (9.70 - 6.04) between the Used
Space and Size on Disk.

Question is why ?

Is this normal ?

Thank you

Alan C.Brown

 

[Alan C. Brown]

Did as you instructed and selected show hidden files and folders and show
hidden protected operating system files, and now with all the folders &
files highlighted in the C: partition, clicking on properties gives:

44,793 Files, 2649 Folders
Size: 9.21GB (9,892,328,944 bytes)
Size on disk: 9.10Gb (9,779,005,832 bytes)

Therefore the difference between Size (9.21GB) and Used Space (9.70GB) has
been reduced to 0.49GB (from 3.66GB) - so that explains most of the
difference originally observed. Wonder what the remaining 0.49GB difference
is due to.

I'm amazed at the size/size on disk/used space, considering I've only
installed 82MB of applications.

Confirm that I'm getting Size > Size on Disk (always thought it was supposed
to be the other way around (i.e. with Size on Disk = Size + wasted space).

Thanks for your help.

Alan C. Brown

Firstly there is a reason why the "Size" and "Size on disk" are different.
Space on disks is allocated in chunks which is a whole number of sectors,
so each file occupies a given number of sectors. Now the sector size can
vary, but assuming a 4KB sector size (which is what it is on my pc but
they can vary) then any file less than 4KB will take up a single sector.
So if my file is only 10 bytes long then the majority of that 4KB is going
to waste. On average each file will "waste" half a sector, so in my case I
loose about 2KB for each file. Applying that to your case, 44,671 files
would loose about 2KB*44671 = 87MB which is quite close to the 0.1GB
(100GB) which is the difference beween 6.14 and 6.04GB you have reported.

As for the difference between the "size" of 6.14GB and the "Used space"
figure of of 9.70GB. Normally I would expect the figures to be other other
way round with the total "Size" larger thant he reported "Used space". On
my pc the "size" is 128GB and the "Used space" is only 119GB, this is
because disk capacity is measured assuming 1GB = 1,000,000,000 bytes
whereas file sizes are calculated assuming that 1GB=2^30bytes =
1,073,741,824.

The reason (and now finally we come to the answer you are after) why your
"Used space" is larger than your total file "Size" is almost certainly
because windows hiding hidden and system files from you and that these are
therefore not included in the total. If in Windows Explorer you go tools >
Options and on the "View" tab select to show hidden files and folders and
protected operating system files, then I would expect your "Used space"
figure to increase.

I'm amazed at the size/size on disk/used space, considering I've only
installed 82MB of applications.

 

[Ken Blake, MVP]

Firstly there is a reason why the "Size" and "Size on disk" are different.
Space on disks is allocated in chunks which is a whole number of sectors, so
each file occupies a given number of sectors. Now the sector size can vary,
but assuming a 4KB sector size (which is what it is on my pc but they can
vary) then any file less than 4KB will take up a single sector. So if my
file is only 10 bytes long then the majority of that 4KB is going to waste.
On average each file will "waste" half a sector, so in my case I loose about
2KB for each file. Applying that to your case, 44,671 files would loose
about 2KB*44671 = 87MB which is quite close to the 0.1GB (100GB) which is
the difference beween 6.14 and 6.04GB you have reported.

Although what you say is generally correct, note that space is
allocated in units called "clusters," not sectors.

On hard drives, sector size is fixed at 512 bytes. Cluster size, on
NTFS volumes is normally 4K, but on a FAT32 volume, it varies with the
size of the volume.