BIB-VERSION:: CS-TR-v2.0
          ID:: STAN//CS-TR-73-351
       ENTRY:: September 25, 1995
ORGANIZATION:: Stanford University, Department of Computer Science
       TITLE:: Performance of an I/O channel with multiple paging drums
               (digest edition).
        TYPE:: Technical Report
      AUTHOR:: Fuller, Samuel H.
        DATE:: August 1972
       PAGES:: 9
    ABSTRACT:: For rotating storage units, a paging drum organization is
               known to offer substantially better response time to I/O
               requests than is a more conventional (file) organization
               [Abate and Dubner, 1969; Fuller and Baskett, 1972]. When
               several, asynchronous paging drums are attached to a single
               I/O channel, however, much of the gain in response time due
               to the paging organization is lost; this article investigates
               the reasons for this loss in performance.

               A model of an I/O channel with multiple paging drums is
               presented and we embed into the model a Markov chain that
               closely approximates the behavior of the I/O channel. The
               analysis then leads to the moment generating function of
               sector queue size and the Laplace-Stieltjes transform of the
               waiting time. A significant observation is that the expected
               waiting time for an I/O request to a drum can be divided into
               two terms: one independent of the load of I/O requests to the
               drum and another that monotonically increases with increasing
               load. Moreover, the load varying term of the waiting time is
               nearly proportional to (2 - l/k) where k is the number of
               drums connected to the I/O channel. The validity of the
               Markov chain approximation is examined in several cases by a
               comparison of the analytic results to the actual performance
               of an I/O channel with several paging drums.
       NOTES:: [Adminitrivia V1/Prg/19950925]
         END:: STAN//CS-TR-73-351