Festplattencache

Festplattencache designates the fast buffer of a non removable disk, which on the data medium buffers writing and read accesses, in order to reduce the influence of the latency and data transmission rate of the data medium access to the system.

All at present at the market available non removable disks usually possess several megabyte at fast RAM as buffers.

Cache buffer distinctive with respect to pure Lesecache and Schreibcache: With Lesecache only the data for a renewed use, already loaded from the data medium, become buffered.

With a Schreibcache data can be stored also retarded , whereby the non removable disk processes write accesses from view of the system faster. Here the execution of the write requirement is already announced, as soon as the data are in the Cache. The actual access to the data medium against it takes place only somewhat later. A power failure in this meantime entails usually the loss of the data not written yet. For this case current RAID uses - CONTROLLER a BBU (Battery Backup unit, which guarantees the current supply, until all data from the Schreibcache are written.

Beside this specialized memory in the non removable disk use many operating systems a part of main storage as Cache. For times of MS-DOS on PCs for this purpose the program Smartdrv was often used. In current operating systems this functionality is normally stopped by the system, depending upon existing main storage, the user must usually make no special configuration.

 

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