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Higher performance in hard disk drives comes from devices which have better performance characteristics.〔〔 These devices include those with rotating media, hereby called ''rotating drives'', i.e., hard disk drives (HDD), floppy disk drives (FDD), optical discs (DVD-RW / CD-RW), and it also covers devices without moving parts like solid-state drives (SSD). For SSDs, most of the attributes related to the movement of mechanical components are not applicable, but the device is actually affected by some other electrically based element that still causes a measurable delay when isolating and measuring that attribute.〔 These performance characteristics can be grouped into two categories: access time and data transfer time (or rate).〔 ==Access time== The ''access time'' or ''response time'' of a rotating drive is a measure of the time it takes before the drive can actually transfer data. The factors that control this time on a rotating drive are mostly related to the mechanical nature of the rotating disks and moving heads. It is composed of a few independently measurable elements that are added together to get a single value when evaluating the performance of a storage device. The access time can vary significantly, so it is typically provided by manufacturers or measured in benchmarks as an average.〔〔 For SSDs this time is not dependent on moving parts, but rather electrical connections to solid state memory, so the access time is very quick and consistent.〔 Most testing and benchmark applications do not draw a distinction between rotating drives and SSDs so they both go through the same measurement process. The key components that are typically added together to obtain the access time are:〔〔 *Seek time *Rotational latency *Other * *Command processing time * *Settle time 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Hard disk drive performance characteristics」の詳細全文を読む スポンサード リンク
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