Ken W. Shirriff

Measurements of a distributed file system

We analyzed the user-level file access patterns and caching behavior of the Sprite distributed file system. The first part of our analysis repeated a study done in 1985 of the: BSD UNIX file system. We found that file throughput has increased by a factor of 20 to an average of 8 Kbytes per second per active user over 10-minute intervals, and that the use of process migration for load sharing increased burst rates by another factor of six. Also, many more very large (multi-megabyte) files are in use today than in 1985. The second part of our analysis measured the behavior of Sprites main-memory file caches. Client-level caches average about 7 Mbytes in size (about one-quarter to one-third of main memory) and filter out about 50% of the traffic between clients and servers. 35% of the remaining server traffic is caused by paging, even on workstations with large memories. We found that client cache consistency is needed to prevent stale data errors, but that it is not invoked often enough to degrade overall system performance.

Performance and design evaluation of the RAID-II storage server

RAID-II is a high-bandwidth, network-attached storage server designed and implemented at the University of California at Berkeley. In this paper, we measure the performance of RAID-II and evaluate various architectural decisions made during the design process. We first measure the end-to-end performance of the system to be approximately 20 MB/s for both disk array reads and writes. We then perform a bottleneck analysis by examining the performance of each individual subsystem and conclude that the disk subsystem limits performance. By adding a custom interconnect board with a high-speed memory and bus system and parity engine, we are able to achieve a performance speedup of 8 to 15 over a comparative system using only off-the-shelf hardware.

Generating fractals from Voronoi diagrams

Abstract This paper describes how to generate fractal patterns by recursively creating Voronoi diagrams on a set of points. These patterns resemble such things as leaf veins and roadmaps. By varying the degree of subdivision and the distribution of points, different output patterns can be obtained.

Fractals from Simple Polynomial Composite Functions

This paper describes a method of generating fractals by composing two simple polynomial functions. Many common fractals, such as the Mandelbrot set, the tricorn, and the forced logistic map, as well as new fractals can be generated with this technique. In many cases, the symmetry of the resulting fractal can be easily proved.

An investigation of fractals generated by z → 1z^n + c

Abstract This paper explores methods of generating fractals from the mapping z → z−n + c and discusses the structure of the resulting images. Lyapunov exponents and cycle periodicity show details of these fractals that are obscured by prior escape-time techniques. The resulting fractals are shown to have a hypocycloid shape. The associated Julia sets can be classified into a variety of types.

The RBW color model

Abstract This paper introduces a new color model, RBW, which can be used as an intuitive user-interface for selecting colors in computer graphics systems. It is based on the red-green, blue-yellow, and white-black color axes. These axes are similar to the axes in opponent color theory, but their semantics are different: In the RBW model, the white-black axis mixes white or black into the color rather than controlling the achromatic brightness. The RBW model has the advantages of opponent color models plus additional benefits: The color gamut has a simple cubical shape, color coordinates are assigned according to simple rules, and all basic colors are at gridpoints in the cube.

Chapter 4 – Generating fractals from Voronoi diagrams

Publisher Summary Voronoi diagrams can be used to generate interesting fractal patterns that resemble leaf veins, roadmaps, and cracked pottery glaze. The patterns are generated by recursively creating a Voronoi diagram inside each Voronoi polygon. A Voronoi diagram consists of nearest-neighbor polygons. To generate the fractal images, one starts with a small set of points and draws the Voronoi diagram of these points. Then, a denser set of points is used and a new Voronoi diagram is computed inside each region of the first diagramFor each region only the points inside that region are considered, and a Voronoi diagram is drawn clipped to that region. This process is repeated recursively, building a new Voronoi diagram inside each region of the higher-level diagram. The output can be varied in several ways. The most obvious parameters are the number of points at each level and the total recursion depth.

An investigation of fraclas generated by z→1/z∧n+c

Publisher Summary This chapter explores methods of generating fractals from the mapping z → z-n + c and discusses the structure of the resulting images. Lyapunov exponents and cycle periodicity show details of these fractals that are obscured by prior escape-time techniques. The resulting fractals are shown to have a hypocycloid shape. The associated Julia sets can be classified into a variety of types. In general, the Julia sets are not symmetrical by reflection unless c is real. A positive Lyapunov exponent indicates chaotic behavior and a negative Lyapunov exponent indicates stable behavior.

Decoding a VCR controller code

The VCR Plus+ is a remote control for programming video cassette recorders. It uses an encrypted 1 to 8 digit number that encodes the channel, start time, length, and day of the month of the television show to be recorded. This paper describes a procedure for decoding the 1 to 6 digit codes.