ABB PM866K01 3BE050198R1 数字继电器输出模块

ABB PM866K01 3BE050198R1 数字继电器输出模块

In modern computers, hard disk drives (hard disks) or solid state disks (solid state disks) are usually used as auxiliary storage. This access time is usually in milliseconds (thousandths of a second) per byte of hard disk or solid state disk, while the access time per byte of main storage is in nanoseconds (billionths of a second). Therefore, secondary storage is much slower than primary storage. The access time of rotating optical storage devices, such as compact discs and digital disc drives, is even longer. Other examples of auxiliary storage technologies include usb flash drives, floppy disks, magnetic tapes, paper tapes, punched cards, and RAM disks.

Once the disk read/write head is on the HDD, it reaches the appropriate position, and the data and subsequent data on the track can be accessed very quickly. In order to reduce seek time and rotation delay, data is transferred to or from disk in the form of large continuous blocks. Sequential or block access on disk is several orders of magnitude faster than random access, and many complex paradigms have been developed to design efficient algorithms based on sequential and block access. Another way to reduce I/O bottleneck is to use multiple disks in parallel to increase the bandwidth between main memory and auxiliary memory. [5]

The concept of virtual memory used by most computer operating systems allows the use of more main storage capacity than the physical available capacity in the system. As the main memory fills up, the system will copy the least used blocks (pages) to the swap file or page file on the auxiliary memory, so as to retrieve them later when needed. If a large number of pages are moved to slower secondary storage, system performance will be degraded.