中央处理机的速度已经高到这样的程度,使得整机的性能取决于存储器的速度。然而,提供一个高性能大容量的主存储器是不经济的。于是,在计算机系统存储器的设计中便出观了从快速而昂贵到慢速而造价较低的不同装置的存储器体系。在存储器体系中最重要的子系统是电-磁旋转式存储器,如磁盘驱动器。计算机系统的可靠性和联机的磁盘存储器的可靠性有着直接的关系。在计算机系统中,像任何高速数据传输系统一样,最严重的问题之一是发生数据错误。磁盘存储器的数据错误有两种表现形式:“软”的和“硬”的。前者是由系统中的电磁干扰引起的,其性质是间断的,并且这种错误可通过把数据再次传送操作的方法得到校正。后者是由记录介质固有的缺陷以 Central processing speed has been so high, so that the performance of the machine depends on the memory speed. However, it is uneconomical to provide a main memory of high performance and large capacity. Thus, in the design of computer system memory, a memory system from different devices that are fast and expensive to slow and at a lower cost is presented. The most important subsystem in the memory system is electro-magnetic rotary memory such as disk drives. The reliability of computer systems is directly related to the reliability of online disk storage. In computer systems, like any high-speed data transfer system, one of the most serious problems is the occurrence of data errors. There are two manifestations of disk storage data errors: “soft ” and “hard ”. The former is caused by electromagnetic interference in the system, its nature is intermittent, and this error can be corrected by sending the data again. The latter is caused by the inherent defect of the recording medium