SIMPLE: An optimal disk system with two restricted heads

doi:10.1016/0020-0190(95)00112-P

Information Processing Letters

Volume 55, Issue 5, 15 September 1995, Pages 273-277

https://doi.org/10.1016/0020-0190(95)00112-P Get rights and content

Abstract

Two-headed disk systems are now commercially available. In this paper, we consider a two-headed disk system, named SIMPLE, whose two heads are locked in a fixed number of cylinders and must staid within the disk surface. We call these heads restricted. We analyze the amortized complexity of SIMPLE and find that it is an optimal disk system with two restricted heads. Moreover, compared with our previous results, we obtain that SIMPLE performs more than twice as well as a system with only one head. Our result matches the conclusion of the previous studies in which two-headed disk systems have been analyzed based on some probability models.

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The k-Client Problem
2001, Journal of Algorithms
Virtually all previous research in online algorithms has focused on single-threaded systems where only a single sequence of requests compete for system resources. To model multithreaded online systems, we define and analyze the k-client problem, a dual of the well-studied k-server problem. In the basic k-client problem, there is a single server and k clients, each of which generates a sequence of requests for service in a metric space. The crux of the problem is deciding which client's request the single server should service rather than which server should be used to service the current request. We also consider variations where requests have nonzero processing times and where there are multiple servers as well as multiple clients.
We evaluate the performance of algorithms using several cost functions including maximum completion time and average completion time. Two of the main results we derive are tight bounds on the performance of several commonly studied disk scheduling algorithms and lower bounds of $lg k 2 + 1$ on the competitive ratio of any online algorithm for the maximum completion time and average completion time cost functions when k is a power of 2. Most of our results are essentially identical for the maximum completion time and average completion time cost functions.

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Information Processing Letters

SIMPLE: An optimal disk system with two restricted heads

Abstract

Should the two-headed disk be greedy? — Yes, it should

Inform. Process. Lett.

Competitive algorithms for server problems

J. Algorithms

Optimum head separation in a disk system with two read/write heads

J. ACM

Sequencing problems in two-server systems

Math. Oper. Res.

Amortized analysis of some disk scheduling algorithms: SSTF, SCAN and N-step SCAN

BIT

Amortized analysis of disk scheduling algorithm V(R)

J. Inform. Sci. Engineering

The k-Client Problem