Report Number: CS-TR-72-317
Institution: Stanford University, Department of Computer Science
Title: An analysis of drum storage units.
Author: Fuller, Samuel H.
Author: Baskett, Forest
Date: August 1972
Abstract: This article discusses the modeling and analysis of drum-like storage units. Two common forms of drum organizations and two common scheduling disciplines are considered: the file drum and the paging drum; first-in-first-out (FIFO) scheduling and shortest-latency-time-first (SLTF) scheduling. The modeling of the I/O requests to the drum is an important aspect of this analysis. Measurements are presented to indicate that it is realistic to model requests for records, or blocks of information to a file drum, as requests that have starting addresses uniformly distributed around the circumference of the drum and transfer times that are exponentially distributed with a mean of 1/2 to 1/3 of a drum revolution. The arrival of I/O requests is first assumed to be a Poisson process and then generalized to the case of a computer system with a finite degree of multiprogramming. An exact analysis of all the models except the SLTF file drum is presented; in this case the complexity of the drum organization has forced us to accept an approximate analysis. In order to examine the error introduced into the analysis of the SLTF file drum by our approximations, the results of the analytic models are compared to a simulation model of the SLTF file drum.