External article
MSDN
Creating Custom Timer Jobs in Windows SharePoint Services 3.0
Contents
- Introduction to Windows SharePoint Services Timer Jobs
- Creating Custom Timer Jobs
- Configuration Options
- Deploying Custom Timer Jobs
- Debugging Custom Timer Jobs
Many different types of applications require some variation of a scheduled process to run. These processes are used for complex calculations, notifications, and data validation checks, among many other tasks. Windows SharePoint Services is no exception. To return relevant and timely results to users’ search queries, the content within a server farm must be indexed ahead of time. This indexing is performed at scheduled intervals. Search is only one example; another example might be sending nightly or weekly e-mail messages to users who want to be notified when changes occur in a SharePoint list. These scheduled tasks are handled by the SharePoint Timer service, a Windows service that is set up as part of the installation process.
Read on MSDN
The publisher hosts the canonical version — this page is a pointer with the details.