Although computing hardware has become increasingly more powerful, computer responsiveness is still an important issue due to multi-tasking and software bloat. We propose a holistic approach for improving computer responsiveness through user focus-aware resource management for CPU, memory, disk I/O, and graphics processing. Previous approaches only address one or two of these problems simultaneously. To the best of our knowledge, our work is the first to address disk I/O scheduling for better responsiveness. It also offers better solutions for the other problems. We also exploit the user-perceived latency to perform dynamic voltage scaling of the CPU to reduce power consumption at run-time without sacrificing responsiveness. We implemented our approach in the Linux/X Window system (henceforth referred to as Linux/X) on an IBM Thinkpad R32 laptop with mobile Pentium 4-M processor, which has two performance levels with different frequency/supply voltage settings: high (30.0W at 1.8GHZ/1.3V) and low (20.8W at 1.2GHz/1.2V). Experimental results show that user focus-aware resource management achieves a significant improvement in computer responsiveness and some in energy efficiency. For example, for TuxRacer, a video racing game, with GpsDrive, a navigation system, running in the background, it provides a reduction of 42.0% in user-perceived latency and 7.5% in energy consumption with respect to the Linux/X system.