Issues and problems in the I/O subsystem. I. The magnetic disk

For many years, processor cycle times have continued to increase at a very rapid rate. On top of this, advances in multiprocessor technology have allowed potential system performance to increase at an even faster rate. The result is that the performance of many of today's computer systems is limited by the I/O subsystem. In this paper, the authors attempt to do two things: (1) separate I/O space into three categories, based on their very different raisons d'etre and consequently very different characteristics, and (2) focus on the issues pertaining to improving the performance of one basic mechanism in the I/O subsystem, the magnetic disk. They do the former in order to set the framework of the I/O space. (If one is to improve the performance of the I/O subsystem, one, first has to understand the nature of I/O and not cloud one's efforts by treating I/O as one homogeneous structure.) They do the latter as the first step in dealing with the various mechanisms that make up the I/O space.<>