This code is a companion to the paper "Sequential File Programming Patterns and Performance with .NET" by Peter Kukol and Jim Gray, MSR-TR-2004-136. It contains 4 projects. (1) IOexamples shows the simple design patterns for doing sequential file access in .NET. (2) AsyncIO shows how to do unbuffered AsyncIO in .NET (3) FragDisk is a utility that creates many files on a volume and so leaves it fragmented. (4) IOspeed is a utility used to measure the speed of file access from a disk. It was used to generate the performance numbers in the technical report. All the code is in C# and uses VisualStudio2005 and the .NET 1.8 runtime.