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A surface test is a scan of a hard drive that is performed to look for bad sectors. Data stored in a bad sector can be corrupted or lost, and identifying bad sectors allows them to be flagged so that the computer knows not to use them in the future. Many of the software programs for computer maintenance which come loaded with operating systems include a surface test feature, and it is also possible to use a program specifically designed for surface testing to scan a drive.
When a hard drive is manufactured, it usually contains some bad sectors. Over time, more can develop. These areas of the hard drive are damaged in a way which impairs their function, either partially or totally. A number of events can lead to a bad sector, from physical damage caused by faulty components to damage which is the result of a crash or unexpected shutdown. A surface test does what it implies — it scans the surface to check for bad sectors. It is important to note that having bad sectors is not necessarily dangerous or harmful, as long as they are identified and isolated.
The test identifies bad sectors by reviewing the hard drive and looking for disk read errors which indicate that there is a problem with a given sector. Some programs can attempt to repair bad hard drive sectors while performing a hard drive test. Others will mark those sectors so that the system knows not to use them. It may allow them to be read, in case the data stored on the bad sector is still accessible, but they cannot be written to.
It is advisable to run tools for computer maintenance, such as a surface test and hard drive defragmenter, on a regular basis. Checks for viruses, bad sectors, and other problems can allow people to identify them early, before they develop into a more serious issue. This can be scheduled to happen automatically, for computer users who are worried that they might forget otherwise. Software included with an operating system is usually up to the job, but users can also download specialty programs. It is important to use a program which is designed for the operating system and file system in use, and to obtain programs from reputable companies.
The term "surface test" is also used in other senses, such as materials testing, where the goal is to physically test a surface. Surface tests of this nature are performed for product quality control and to confirm that a surface is usable.