Table 1: Important Performance Monitor Counters
Performance Object	Counter	Information Provided
Memory	Available Bytes	Shows the current available physical memory on the system. As this number gets lower, Windows starts aggressively paging to disk. When the number is very low (i.e., less than 5MB available), the system spends most of its time paging.
Memory	% Committed Bytes in Use	Shows the percentage of all allocated memory, compared with the maximum available. This metric includes the virtual memory footprint for all running applications, rather than just their physical memory usage. This counter is important because as the number reaches 90 percent, Windows attempts to grow the pagefile to accommodate the additional memory needs. Pagefile expansion degrades performance. If this counter is at or near its maximum during your system's usual operation, you should increase the minimum pagefile size.
Network Interface	Bytes Total/sec	Shows per-NIC statistics for how much traffic is flowing in and out of your server.
Physical Disk	% Busy Time	Shows how much time a physical disk is spending satisfying requests. If this counter is consistently high, either you don't have sufficient RAM on the system (i.e., the system is having to go to disk rather than cache) or your disks are too slow and can't keep up with the application's usage patterns.
Processor	% Processor Time	Shows the percentage of time the system isn't idle (i.e., is working), which can help identify the CPU as the bottleneck in an application.
Server Work Queues	Queue Length	Similar to % Processor Time, queue lengths of more than 4 to 6 for sustained periods might mean that the CPU is causing a bottleneck.
TCP	Segments Retransmitted/sec	For TCP-based applications and in conjunction with the Queue Length counter, large numbers of retransmissions indicate that the TCP/IP stack can't keep up with the flow of requests.