Prime95 vs Linpack: FFT Verification vs Floating-Point Load

Unlike the other comparisons on this site, Linpack is not a single program you download and open. It is a benchmark workload with a long history in measuring how fast computers solve dense floating-point problems, and its code and descendants show up inside other tools. When a tuning utility or testing suite offers a Linpack stress option, it is using that style of workload to load the processor. Understanding that helps set expectations: you are choosing a type of load, not just a brand.

Prime95, written by George Woltman for GIMPS and distributed as freeware, uses Fast Fourier Transform calculations drawn from prime number research. In Torture Test mode it runs those calculations continuously, in sizes chosen automatically from your CPU cache since version 29.8, and compares the output with known correct results. Smallest and Small FFTs keep data in cache and maximise CPU stress, Large FFTs reach into memory and stress the controller and RAM, and Blend, the default, mixes all of it. The test is therefore both a load and an audit.

Different loads, different lessons

A Linpack run teaches you about throughput and short-term behaviour under a particular kind of floating-point pressure: how the CPU handles dense mathematical work, how quickly heat builds, and whether an obviously unstable setting fails fast. Because the workload is also a benchmark at heart, its results can be compared across runs, which suits tuning sessions where you change one setting at a time.

A Prime95 run teaches you about correctness over duration. Heat soaking alone changes the picture: a cooler that handles a short burst may saturate over an hour, memory temperatures climb slowly, and marginal voltages that survive minutes can produce a wrong result much later. The official stress.txt guide is explicit that errors have surfaced after hours and occasionally far longer, which is why it recommends 6 to 24 hours for a thorough check. Neither lesson replaces the other, but only one of them is an audit of answers.

The AVX power question, labelled honestly

Both workload families can use AVX instructions on processors that support them, and AVX code paths are a large part of why modern stress loads run so hot. In Prime95, AVX optimisation entered the FFT code in the 27.x series, FMA support followed, and AVX-512 FFT support arrived in version 29.8, all recorded in the program’s own change history. The program also lets you turn those paths off by adding settings such as CpuSupportsAVX=0 to prime.txt, which lowers the intensity of the test and therefore changes what a pass proves.

Beyond those documented facts, treat temperature claims carefully. Community guides, including long-running enthusiast discussions around older Intel generations, have reported that AVX workloads can run markedly hotter than the older pre-AVX version 26.6 on those platforms. That is community-reported experience on specific older hardware, not an official figure and not a number to apply to a modern processor with different power limits and boost behaviour. We label it as community context here for exactly that reason. If AVX heat is your practical problem, our guide to the AVX offset explains the platform setting that lowers clocks under AVX load on Intel systems.

Side-by-side comparison

Dimension	Prime95	Linpack (as a workload)
What it is	A complete program whose Torture Test verifies FFT calculations	A floating-point benchmark workload embedded in tools such as Intel XTU and OCCT’s Linpack mode
Primary job	Long CPU and RAM stability verification	Performance measurement and short, heavy CPU load generation
How it detects problems	Compares every result against a known correct answer; a mismatch stops the worker	Problems appear as failures to complete, crashes or inconsistent run behaviour, depending on the host tool
Memory coverage	Large FFTs and Blend deliberately stress the memory controller and RAM	Memory load depends on the host tool’s configuration; not a dedicated memory verification method
Typical run style	Hours, following the official 6 to 24 hour guidance for a thorough check	Short runs and repeated bursts inside a tuning or screening session
Power and heat	Sustained maximum in Small FFTs by design; AVX paths can be disabled in prime.txt, which also weakens the test	Can draw very high power in bursts when AVX code paths are active; behaviour varies by host tool and settings
Best question it answers	Do CPU and memory stay correct under sustained load?	How does this CPU perform and behave under dense floating-point load right now?

When to use each approach

Use a Linpack mode when you are tuning and want a repeatable, intense load inside a tool you already use for monitoring or clock changes. It is a fast way to compare settings and to expose settings that are unstable in an obvious way. Keep runs supervised, because burst loads can push temperatures up quickly, and remember that the host tool, its version and its settings all shape the result.

Use Prime95 when you need the final word on a configuration you plan to keep. Run it long, run the preset that matches your worry, and take any worker error seriously: the program’s own documentation says an error usually points to hardware, cooling or settings, not to a software fault, unless the identical error repeats at the identical place every time. The best-known single-purpose wrapper of this workload is covered in our Prime95 vs IntelBurnTest comparison.

Bottom line

Linpack loads a CPU hard and measures it; Prime95 loads a CPU hard and audits it. Short tuning sessions benefit from the first, final stability decisions need the second. The wider tool landscape is mapped on the alternatives and comparisons hub, so you can place both approaches alongside suites, benchmarks and memory specialists before you test.