引言电子数字计算机在商业方面的广泛应用要求用相应的外部设备来存储由计算机产生并供其再次使用的大量数据。这些大量的外部数据在以前主要是用穿孔卡片和磁带来存储的。这些存储装置固有的缺点是:只能串行地取数以及缺乏从存储装置中联机取出全部数据的能力。由于上述缺点再加上对在计算机控制下的大容量、半随机取数、联机数据存储的需要,因此便发展了大型磁鼓、多条短磁带的磁带机以及开展了磁盘的初期研制工作。大型磁鼓能提供毫秒量级的取数时间,但存储容量有限;每一鼓只能存一百万或两百万位信 Introduction The widespread commercial use of electronic digital computers requires the use of appropriate external devices to store large amounts of data generated by the computer and reused. These large amounts of external data were previously stored mainly on punch cards and magnetic tapes. The inherent drawbacks of these storage devices are that they can only be accessed serially and lack the ability to pull all the data online from the storage device. Due to the above shortcomings, coupled with the need for large-capacity, semi-random access, and on-line data storage under the control of a computer, a large drum, a plurality of short tape tape drives, and an initial development of a magnetic disk have been developed. Large drums provide fetch times in the millisecond range but with limited storage capacity; each drum can only hold one million or two million bits