Write-back cache is a caching technique common in most processor architectures since Intel 80486. When required, it copies data to higher level caches, backing store or memory. Write-back cache is also known as write-behind cache and copy-back cache.
Native command queuing (NCQ) is a technology enabling SATA hard drives to accept more than one command at a time by optimizing the order in which read and write commands are executed. This increases the performance of the drive by limiting the number of drive head movements when multiple read/write requests are queued.
NCQ replaces tagged command queuing (TCQ), which is used with parallel ATA (PATA). The manner in which TCQ interacts with the operating system (OS) taxes the CPU in return for little performance gain.Both in the hard drive and in the SATA host bus adapter, NCQ must be supported and enabled and the proper driver must be loaded into the OS. Some OSs include the required generic drivers (such as Windows Vista and Windows 7) whereas others require vendor-specific drivers to be loaded to enable NCQ, like Windows XP.NCQ may also be used in solid-state drives (SSDs), drives containing data in non-volatile memory chips and contain no moving parts. Here, latency (the delay in processing commands) is found on the host not on the drive. The drive uses NCQ to ensure it has commands to process while the host adapter is processing CPU tasks.
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