OCCT

OCCT is a free hardware stress testing and monitoring tool for Windows. It runs intensive tests on your CPU, GPU, memory, and power supply to detect instability caused by overclocking, overheating, or failing components. The program monitors temperatures, voltages, and clock speeds in real time and automatically stops when it detects errors.

What it does

The CPU stress test pushes all cores to maximum load using either OCCT's own algorithm or Linpack. You set a duration and hit Play. During the test, the monitoring panel on the right shows live graphs of temperature, frequency, voltage, and power draw. If the CPU produces calculation errors or exceeds your temperature limit, the test stops immediately and flags the problem.

GPU testing renders a demanding 3D scene to stress the graphics card, while a separate GPU memory test writes patterns to VRAM to find defective memory cells. The Power test loads both CPU and GPU simultaneously to push the power supply to its limits. If your PSU cannot deliver clean, stable power under full load, this test will expose it. RAM testing checks physical memory for bit errors using read-write pattern verification.

After each test, OCCT saves detailed graphs as PNG files and a CSV log with all sensor readings. This gives you a complete record of how your hardware behaved under stress, useful for comparing before and after overclocking changes or diagnosing intermittent crashes.

Who it is for

I use OCCT after every overclocking change to verify stability before trusting the system for daily work. If you have built a new PC, adjusted voltages in BIOS, or experience random crashes, OCCT will tell you within minutes whether your hardware is stable. For users who never overclock and have no stability issues, there is little reason to run it.