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:
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.
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.
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