Given the following characteristics, tuning which resource will provide the greatest benefit? CPU=80% busy Physical Memory=90% used Disks=80% busy Network=80% used File systems are 90%full.

While memory at 90% is high and causes paging, adding memory addresses only the paging component of disk I/O; the remaining disk busy load from filesystem operations and application I/O would keep disks heavily utilized.

Network at 80% utilization is not the highest single metric and does not compound with other subsystems in the way disk I/O and filesystem fullness interact.

Disks at 80% busy combined with filesystems at 90% full represents a compounded I/O bottleneck - near-full filesystems cause fragmentation and inefficient allocation, increasing the I/O burden on already-saturated disks. Additionally, physical memory at 90% used drives active paging to disk, meaning disk improvements simultaneously relieve paging pressure, reducing the impact of the memory constraint as well.

Filesystem fullness at 90% is a capacity symptom of the disk subsystem; tuning the disk subsystem directly (choice C) addresses both the I/O busy percentage and the capacity issue simultaneously.