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.