CPU

Step-by-step CPU check when buying or for yourself. Works for new and used processors.

1

Quick check

5 minutes

  1. Device Manager

    The CPU is detected correctly, no hidden devices with errors.

  2. Basic info

    Match the model and base frequency via System Information or CPU-Z.

  3. Load test

    Run the online CPU test — check compute speed, stability and possible performance drops.

    Open online test →
2

Medium check

10–15 minutes

  1. Monitoring

    Run HWMonitor: check core temperatures at idle and the voltage (Vcore).

  2. Load

    Compress a large file or run a heavy render. The frequencies must not drop.

3

Full check

30–45 minutes, special utilities required

  1. Stress test

    AIDA64 (System Stability Test) or OCCT: 100% load on all cores for 15–20 minutes.

  2. Throttling check

    Make sure the temperature graph is flat and frequencies do not drop from overheating.

  3. Benchmark

    Cinebench (R23 or 2024): compare the score with results of the same CPU online.

Related checklists

Graphics cardRAMPower supply

How to test a CPU before buying — full guide

Testing a CPU before buying is one of the most important steps when picking a used computer or laptop. Processors rarely fail completely, but they can have hidden issues: overheating from dried thermal paste, throttling from a dust-clogged heatsink, power limits in BIOS or mismatched specs. This checklist will help you test a processor step by step, from a quick visual check to a full stress test.

The quick check takes 5 minutes and requires no software. Open System Information in Windows (Win + R → msinfo32) and match the CPU model and base frequency to what the seller claims. Open Device Manager → Processors — the number of entries should match the thread count. For example, a Core i5-12400 has 6 cores and 12 threads, so there should be 12 entries. If the count does not match, the system may not see all cores, which points to a problem. Run the online CPU test right in the browser — it will show compute speed and stability under load.

The medium check takes 10–15 minutes and includes temperature monitoring and real load. Install HWMonitor or HWiNFO64 — free sensor reading tools. At idle, core temperatures should be 30–50°C, up to 60°C on laptops. Run a heavy task: compress a large file, render video, or run the FullTestPC CPU stress test. Watch the temperatures: if they exceed 85–90°C and the CPU starts dropping frequencies — that is throttling, a sign of overheating. Also check the Vcore voltage: a significant deviation from typical values for your model may indicate a motherboard or BIOS problem.

The full check takes 30–45 minutes and requires specialised tools. Run OCCT or AIDA64 System Stability Test — they create maximum load on all cores. Run the test for 15–20 minutes and watch the temperature graph: it should be flat or rise smoothly, with no sharp spikes. If the temperature jumps by 10–15°C in a second — there is a contact issue between the CPU lid and the cooler. In parallel, run Cinebench R23 or 2024 and compare your score with online results for the same CPU — a difference of more than 10% indicates a problem.

Common CPU issues to watch for. Dried thermal paste is the most common cause of overheating in used tech, fixed by repasting for a small cost. A dust-clogged heatsink is cleaned with compressed air. Power issues on the motherboard show up as unstable frequencies and require a board replacement. Mismatched specs — selling a lower-end CPU disguised as a higher-end one — is checked by core and thread count. Avoid processors with damaged contacts (AMD AM4/AM5) or cracks on the PCB — these cannot be fixed. If all tests pass and specs match — the CPU is healthy and ready to work.