.NET news » Performance 
Identifying NHibernate-Related Bottlenecks through Performance Monitoring
Simple Performance Chart
Optimizing integer divisions with Multiply Shift in C#
Speed Testing and the Stopwatch Class
Improving ASP.NET Application Performance and Scalability
Some Useful Concurrency Classes and A Small Testbench
Implementing the CLR Asynchronous Programming Model
Slow and unpredictable are words that typically characterize I/O operations. When an application performs a synchronous I/O operation, the application is basically giving up control to the device that is doing the actual work. For example, if an application calls the StreamRead method to read some bytes from a FileStream or NetworkStream, there is no telling how much time will pass before that method returns. If the file being read is on a local hard drive, then Read may return almost immediately. If the remote server housing the file is offline, then the Read method may wait several minutes before timing out and throwing an exception. During this time, the thread making the synchronous request is tied up. If that thread is the UI thread, the application is frozen and stops responding to user input.
A thread waiting for synchronous I/O to complete is blocked, which means that thread is idle but is not allowed to perform useful work. To improve scalability, many application developers create more threads. Unfortunately, each thread introduces significant overhead such as its kernel object, user-mode and kernel-mode stacks, increased context switching, the calling of DllMain methods with thread attach/detach notifications, and so on. The result is actually reduced scalability.
An application that wishes to remain responsive to the user, improve scalability and throughput, and increase reliability should not perform I/O operations synchronously. Instead, the application should use the common language runtime (CLR) Asynchronous Programming Model (APM) to perform asynchronous I/O operations..

