unaccounted hard drive memory space

see if this program helps you to ascertain what is taking up the space:

http://www.jam-software.com/treesize_personal/

system restore by default will take up to 15% of the hard drive capacity

you may like to diminish that amount

http://www.vistax64.com/tutorials/76227-system-restore-disk-space.html

http://www.vista4beginners.com/System-Restore-Space-Used

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Disk Cleanup:

Delete files using Disk Cleanup

http://windows.microsoft.com/en-US/windows-vista/Delete-files-using-Disk-Cleanup

The More Options tab is available when you choose to clean files from all users on the computer. This tab includes two additional ways to free even more disk space:

• Programs and Features. Opens Programs and Features in Control Panel, where you can uninstall programs that you no longer use. The Size column in Programs and Features shows how much disk space each program uses.

• System Restore and Shadow Copies. Prompts you to delete all but the most recent restore point on the disk.

  System Restore uses restore points to return your system files to an earlier point in time. If your computer is running normally, you can save disk space by deleting the earlier restore points.

  In some editions of Windows Vista, restore points can include previous versions of files, known as shadow copies, and backup images created with Windows Complete PC Backup. This information will also be deleted. For more information about System Restore, search Windows Help and Support for "system restore.

•  

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also  scan for malware

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and read this microsoft information on optimizing windows

http://windows.microsoft.com/en-US/windows-vista/Optimize-Windows-Vista-for-better-performance

thank you for taking the time to respond to my question.

the problem I have is that I deleted 55 GB worth of files from the HD, but only 30 GB were added to the HD free space.

Even when I did all of the above ( which I did before writing) I still did not see all the 55 GB added to mhy HD free space?

So the question is: what happened to the 25 GB?

did you use that program in my original reply to see WHAT is taking up that space??

see if this program helps you to ascertain what is taking up the space:

http://www.jam-software.com/treesize_personal/

and also this?

system restore by default will take up to 15% of the hard drive capacity

you may like to diminish that amount

http://www.vistax64.com/tutorials/76227-system-restore-disk-space.html

http://www.vista4beginners.com/System-Restore-Space-Used

Hello and thanks again for taking the time to respond.

Yeah, I used the jam application and scanned with malware bytes before writing here.

My Original Hard Drive is 350 GB, but it shows that 291 GB are only available due to space taken up by system restore etc...

Of the 291 GB,  there are 20 GB unaccounted for.

Changing the system restore capacity will not resolve the issue.

There's logical disk and physical disk

Physical disks correspond to the hardware. Physical disks have sectors,
tracks, cylinders, etc. Physical disks can be divided into logical drives.
For example one physical disk on a computer can be divided into logical
drives C: and D:. Users interact with logical drives. Logical drives have
properties like disk space.
Richard Mueller
MVP Directory Services
Hilltop Lab - http://www.rlmueller.net

"Think about the number of times you open a document file in MS Word but do not scroll all the way through it.) Lazy write deferred disk updates occur sometime after the original logical file request. The update needs to be applied to the physical disk, but the required physical disk operation is usually not performed right away. So what is happening at the physical disk right now, as expressed by the current logical and physical disk statistics, is usually not in sync with logical file requests. This is the influence of caching. Caching makes it almost impossible to determine which applications are causing a physical disk to be busy except under very limited conditions (when very few applications are using the disk, for example)."

http://technet.microsoft.com/en-us/library/bb742613.aspx

Does that help?

Unfortunatly all the posted answers are not relevant to my question, and I am sorry that my question was not very clear in the first place.

The issue simply is that I deleted 55 GB worth of files from my PC. I expected to see a corresponding increase of 55 GB on my HD free memory, but I only saw an increase of 30 GB. 

I performed several disk clean ups without any change.

When I right click properties of my C drive, I see 55 GB of free space however this space should be 75GB.

I am therfore worried that part of my hard drive is hijacked.

Unfortunatly all the posted answers are not relevant to my question, and I am sorry that my question was not very clear in the first place.

The issue simply is that I deleted 55 GB worth of files from my PC. I expected to see a corresponding increase of 55 GB on my HD free memory, but I only saw an increase of 30 GB. 

I performed several disk clean ups without any change.

When I right click properties of my C drive, I see 55 GB of free space however this space should be 75GB.

I am therfore worried that part of my hard drive is hijacked.

 

Maybe this will explain it better.

Why does space used by files on my harddrive show different numbers depending on how I look.

http://tinyurl.com/cgoj7g

And have you emptied your recycle bin, lol.