How To Fix Disk Surface Errors

Hard disk drives in your computer system use a small circular plate coated with a magnetic surface. This disk rotates at speeds in excess of 5,000 rpm. The machine's operating system uses a circular grid layout to index positions on the disk surface. The disk indexing system consists of:

• Tracks, which are circular and concentric.
• Disc sectors, which are radial blocks.

The overall storage size of the disk, the number of tracks and sectors explains the minimum storage block size on any individual disk, and this dictates propensity for file fragmentation. See my other HowToDoThings article on improving your computer's hard disk response. Small HDD's have smaller minimum storage blocks than larger capacity units, making storage more efficient for small data files. However, disk storage space costs progressively less with time and no one seems to bother about this.

Modern hard disk drives store upwards of 500GB of data (GB = Gigabyte - 1 Thousand Million bytes) so it is no surprise to find small, minor imperfections on the magnetic surface, which will not record reliably. These small errors are usually found at the factory when an initial 'format' operation is performed.

The location of any disk surface errors can be recorded by the operating system once installed in a machine, so these locations are not used to store data (the technical term for this is that they are 'mapped out' of use).

Once the disk is installed and used normally reliability is good – most disks have a mean time before failure time rated in 100,000's of hours. So hopefully yours will be in the half where the time to failure is longer than the mean! Smaller-size disks (both in storage and physical dimensions) are fitted to most laptop machines – so they require less work to spin the platter around, and the small size is less prone to damage from external forces.

Once running, the disk is designed to be maintenance-free. However, surface coating imperfections are still possible and most operating systems provide disk utility software to allow any faults to be re-assessed and the location information used to avoid using these areas in the future.

1. Run the checkdisk process. Windows includes a checkdisk utility – 'Chkdsk'. This provides a tool which will 'map out' bad disk areas. The term 'bad sectors' is applied to locations on the disk with surface imperfections.
2. From the Command Screen – choose 'Run' from the Start button and type 'cmd' to obtain a terminal screen/window. At the prompt, type 'chkdsk'. There are a number of options – for further information, type '? chkdsk' at the prompt.

   Alternatively:

   From 'My Computer' – select the hard disk with a right mouse click; select 'Properties'; and in the properties window, look under the 'Tools' tab pane. Alternatively you can find this under Programs>Accessories>Scan Disk.

3. The checkdisk software utility will only scan a hard disk provided the disk is not being used for any other purpose. Windows, like all operating systems, is a very complex piece of software, and it may not be obvious that other applications and programs are running, maybe in the background. Even if you try quitting all programs you may find, the 'chkdsk' utility fails to run. It may report this and offer to run during the next re-boot (start-up). This is the safest option – select 'Close' from the Start button and then select Restart. 'Chkdsk' will run before other processes and applications as the machine restarts itself.
4. The utility can simply report what it finds, or you can ask it to 'fix' any problems if possible. If you know the problem you may go straight to 'fix', but if there are any doubts about the causes of problems, it will be safer to ask for a surface scan and check the report before continuing.

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