The Big Three
To bring up System Monitor, click Start > Administrative Tools > Performance. You should see a screen similar to the one shown in Figure 1.
Figure 1 Windows System Monitor.
Notice that there are counters for three objects already running (by default). An object is any system component (that is, service, software, or hardware) that can be measured statistically. A counter is a measurable characteristic of an object. Most objects have many counters. The pages/sec counter for the Memory object is useful to determine Random Access Memory (RAM) shortage in our system. In other words, if we see numerous and consistent spikes in pages/sec, we know that our system is writing memory pages to the hard drive instead of RAM, which results in noticeable slower system performance when accessing and processing instructions for applications or services.
The Avg. Disk Queue Length counter of the Physical Disk object indicates the number of I/O requests waiting for disk access. This number should be no more than 1.5 to 2 times the number of spindles (most disks have one) making up the physical disk. Here's an example: Suppose that you had a database server running on your system. If too many I/O requests are waiting for disk access during database activity, your drive is likely to become saturated, causing poor performance.
The CPU's processor time counter is probably the most straightforward of these three. It indicates the amount of stress on your CPU at any given time. A consistently high value here tells you that your CPU is overstressed. You can also monitor multiprocessor systems using system monitor.
In the Windows 2003 Server version of SM, there are six new counters for the processor object. The first three are %C1, %C2, and %C3 Time. The CPU can operate in any one of these power performance states (C1, C2, or C3). C0 is normal power state; and C1, C2, C3 are the low power states of operation. For example, when a system goes into sleep mode, the operating system will tell the CPU to go into the C3 low power operation state mode (lowest power state). The CPU will then reduce the voltage it's using in terms of power consumption. Although C3 is the lowest state, the other two states are often used by the CPU as well, based on what the operating system thinks it should be running at, relative to how much latency there is. Not all systems support these states, but most new servers are likely to. These counters tell the percentage of time the processor has spent in each state.
The second three counters are C1, C2, and C3 Transitions/sec. These counters indicate the rate at which the CPU enters any one of these states. Both sets of counters become important when monitoring the strain on your server's processor(s).
If your server is a Web server, you'll find the Web Service Performance object useful. This collection of counters mainly deals with user connections and requests relative to one or more Web sites you may be hosting on the said server.