How SSD HCTM Adjusts Power States in Laptop Benchmarking

This article explains how Solid State Drive (SSD) Host-Controlled Thermal Management (HCTM) dynamically adjusts NVMe power states during intensive laptop hardware benchmarking. It covers the mechanics of operational NVMe power states, the role of host-defined temperature thresholds, and how a laptop’s system firmware uses these metrics to balance peak storage performance with thermal safety in a confined mobile chassis.

What is Host-Controlled Thermal Management (HCTM)?

Introduced in the NVMe 1.3 specification, Host-Controlled Thermal Management (HCTM) is a feature that allows the host system (the laptop's BIOS and operating system) to dictate how an SSD manages its temperature. Instead of relying solely on the SSD's internal firmware to panic-throttle when it gets too hot, the laptop sets two specific temperature thresholds on the drive:

• Thermal Management Temperature 1 (TMT1): The threshold for light thermal throttling.
• Thermal Management Temperature 2 (TMT2): The threshold for heavy thermal throttling.

Understanding NVMe Operational Power States

To control heat, HCTM forces the SSD to transition between different NVMe Power States (PS). During an active hardware benchmark, the SSD only uses operational power states, as non-operational states (PS3 and PS4) are reserved for idle or sleep modes.

• PS0 (Maximum Performance): The drive operates at its highest power limit (often 5W to 9W+ in laptops) and delivers maximum read and write speeds.
• PS1 (Light Throttling): Power consumption is capped (typically around 3W to 4W). Performance drops moderately to slow heat generation.
• PS2 (Heavy Throttling): Power consumption is strictly limited (often 1.5W to 2.5W). Performance is significantly reduced to actively cool the drive while maintaining basic I/O functionality.

How HCTM Adjusts Power States During a Benchmark

Laptop benchmarking tools—such as CrystalDiskMark, 3DMark Storage, or PCMark—subject the SSD to sustained read and write queues. In a thin laptop with limited airflow, this causes rapid heat buildup. HCTM manages this stress in four distinct phases:

1. Benchmark Initiation (PS0)

When the benchmark begins, the SSD is in PS0. The controller and NAND flash draw maximum power to deliver peak sequential and random I/O speeds. Because laptops often share heat pipes or thermal zones between the CPU, GPU, and SSD, the ambient temperature inside the chassis rises quickly alongside the SSD's composite temperature.

2. Crossing the TMT1 Threshold (Transition to PS1)

As sustained writes continue, the SSD's temperature sensor hits the host-defined TMT1 limit (commonly set between 70°C and 75°C by laptop manufacturers). HCTM immediately commands the SSD controller to drop from PS0 to PS1. The drive reduces its clock speeds and limits the number of active NAND channels. During the benchmark, you will see a noticeable plateau or a slight dip in megabytes per second (MB/s) and IOPS, preventing the drive from overheating further.

3. Crossing the TMT2 Threshold (Transition to PS2)

If the benchmark is exceptionally long or the laptop’s cooling system is saturated by simultaneous CPU/GPU tests, PS1 may not be enough to stop the temperature from rising. Once the SSD hits the TMT2 limit (often set between 78°C and 83°C), HCTM forces the drive into PS2. Power draw is slashed drastically. Benchmark speeds will plummet—sometimes below SATA SSD levels—to ensure the drive does not reach its critical shutdown temperature (usually 85°C+), which would otherwise crash the benchmark or cause data corruption.

4. Thermal Hysteresis (Returning to PS0)

HCTM uses a mechanism called hysteresis to prevent the SSD from rapidly bouncing between power states. If the drive is in PS2, it will not immediately return to PS1 the moment it drops 1°C below the TMT2 threshold. Instead, the drive must cool down by a predetermined margin (often 3°C to 5°C below the threshold) before HCTM allows it to step back up to PS1, and eventually PS0. This usually occurs during the brief idle pauses between different phases of a benchmark suite.

Why Laptops Rely on HCTM Over Autonomous Throttling

Without HCTM, an SSD relies on autonomous thermal throttling, which only triggers when the drive itself is about to suffer physical damage. In a laptop, waiting that long is dangerous. A blazing-hot SSD running in PS0 can heat-soak the nearby battery, warp thin plastic chassis components, or make the laptop's palm rest uncomfortably hot.

By using HCTM to preemptively step down to PS1 and PS2 during heavy benchmarking, the laptop sacrifices peak synthetic storage scores in favor of system-wide thermal stability and hardware longevity.