Microsoft Windows NT Server 4.0 Resource Kit offers a performance tool, PerfLog, similar to the Datalog service, that captures performance data and writes it to a file. Whereas datalog.exe saves the performance data in the Performance Monitor log format, PerfLog saves the information in a .csv or .tsv file. PerfLog also offers some flexibility in starting new logs at periodic intervals. If you plan to create graphs using a spreadsheet or database package, you might like PerfLog's features. However, if you plan to use Performance Monitor to chart the data, stick with the Datalog service.