An Analysis of Drum Storage Units

摘要

The report 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. (Author)