Disk buffer

A disk cache is the cache server of a hard drive, which buffers read and write accesses to a disk in order to reduce the impact of latency and data transfer rate of the disk access to the system.

Details

2009 available hard drives and solid state drives usually have 8-128 MB RAM as temporary storage.

The cache is divided into pure read cache and write cache. For read cache only the data already loaded from disk for re-use are cached.

A write cache data can also be saved delayed, causing the disk write accesses executes faster from the perspective of the system. Here, the execution of the write request is already reported as soon as the data is in the cache. The actual access to the disk, however, takes place a little later. A power failure in the meantime has mostly the loss of uncommitted data result. For this case, use current RAID controller a BBU ( Battery Backup Unit ), which ensures the power supply until all data is written from the write cache. Another advantage besides lower latency in sporadic write accesses is the possibility of reordering of writes, so that the movements can be minimized within the hard drive.

In addition to this specialized storage in the hard disk itself, many operating systems use a portion of main memory as a cache to speed up access times further by communication over the relatively slow disks bus is eliminated. At the time of MS- DOS was on PCs for this purpose often the program SmartDrive used. In current operating systems, this functionality is normally set by the system depending on the available main memory, the user must make any special configuration in general.