You are using the System Monitor tool on a Windows 2000 computer and you need to determine how much of the paging file (virtual memory) is currently being used during normal operation. Which performance counter should you add in System Monitor to measure the paging file usage percentage?

Introduction / Context:
System Monitor in Windows 2000 allows administrators to track performance counters that describe how memory, disk and processor resources are being used. The paging file is a critical part of virtual memory, and monitoring how full it becomes helps you identify memory pressure or the need to resize the paging file. Choosing the correct performance counter is essential for accurate diagnosis and capacity planning.

Given Data / Assumptions:

• The operating system is Windows 2000.
• You are using System Monitor (formerly Performance Monitor).
• You specifically want to know how much of the paging file is currently in use as a percentage.
• You are not interested in peak values or general memory activity like page faults per second.

Concept / Approach:
The Paging File object in System Monitor exposes two key percentage based counters: Percent Usage and Percent Usage Peak. Percent Usage shows the current percentage of the paging file that is utilized. Percent Usage Peak shows the highest percentage used since the last reboot or reset. Other memory related counters, such as Memory Pages per second or Pool Paged Bytes, refer to different aspects of virtual memory behavior and do not directly show the fraction of the paging file that is allocated at this moment.

Step-by-Step Solution:
Step 1: Open System Monitor and review the available performance objects.Step 2: Select the Paging File object, which contains counters specific to the pagefile.sys usage.Step 3: Inspect the counters under Paging File. Percent Usage displays the current usage as a percentage of the total paging file size.Step 4: Recognize that Percent Usage Peak only records the highest value reached over time, not the present usage.Step 5: Note that Memory Pages per second measures page in and page out operations and is more about activity rate than capacity usage.Step 6: Observe that Memory Pool Paged Bytes is a byte count of paged pool memory, which is different from total paging file utilization.Step 7: Conclude that Paging File Percent Usage is the correct counter to measure how much of the paging file is being used right now.

Verification / Alternative check:
You can verify this by adding both Percent Usage and Percent Usage Peak to the System Monitor graph. As the system runs, the Percent Usage counter fluctuates with current demand, while Percent Usage Peak remains at the highest value achieved. Additionally, Microsoft documentation describes Percent Usage as the correct counter for monitoring current paging file usage, confirming the choice.

Why Other Options Are Wrong:
Paging File Percent Usage Peak shows the maximum percentage used, which is useful for historical analysis but does not show current utilization. Memory Pages per second measures the rate of paging operations and is used to detect thrashing, not capacity. Memory Pool Paged Bytes reports the size of the paged pool, which is only one component of memory usage and does not directly indicate how full the paging file is.

Common Pitfalls:
Many administrators focus only on activity counters like Pages per second and misinterpret high activity as a full paging file, when in reality the paging file might be largely empty. Another pitfall is relying solely on Percent Usage Peak and failing to notice current spikes or trends. For accurate troubleshooting, it is best to view both usage and activity counters, but for the specific question of how full the paging file is at the moment, Percent Usage is the key metric.

Final Answer:
The System Monitor counter that shows how much of the paging file is being used is Paging File-% Usage.