Heat-Assisted Magnetic Recording

HAMR

Seagate’s Mozaic platform is the public face of HAMR in shipping nearline drives; other vendors discuss HAMR on roadmaps or in labs.

In one minute

HAMR briefly heats a nanoscale spot on the platter with a laser-assisted writer so the recording head can flip bits in high-coercivity media that would resist conventional perpendicular writes. The heat pulse is short; vendors use it to push areal density beyond prior PMR/CMR limits on the same 3.5-inch form factor.

Perpendicular recording ran into a materials wall: make bits smaller and the magnet becomes stubbornly stable—good for retention, bad for writing. HAMR’s answer is a staged heat pulse: momentarily soften the spot, write, cool, and lock. Done well, nothing next door notices.

Seagate spent years turning that lab trick into a factory line. Mozaic bundles media (superlattice platinum-alloy stacks in Seagate’s materials), plasmonic writers, and servo/thermal control into SKUs that still speak SATA/SAS to the host. From the rack’s point of view, it is still a hard drive—just more terabytes per slot.

Competitors are not standing still: Toshiba has demonstrated HAMR drives in the lab and discusses test samples on its own timeline. When you read capacity headlines, check whether you are looking at qualified production, customer sampling, or a technology demo.

Compared to neighbors

PMR/CMR widen tracks and improve signal processing without heating. MAMR uses microwave assistance rather than a thermal write pulse. SMR changes track layout; HAMR changes how small and stable each bit can be.

Strengths

Density headroom — Seagate describes Mozaic 3+ at roughly 3TB+ per platter with a path to higher areal density (Seagate HAMR innovation pages).
CMR-class host behavior on HAMR CMR SKUs — Seagate’s public CMR/SMR matrix lists Mozaic HAMR CMR drives alongside conventional Exos lines.
Designed for nearline scale — Seagate positions Mozaic for cloud and hyperscale capacity growth rather than laptop spinners.
ASTC industry view — Seagate cites the Advanced Storage Technology Consortium treating HAMR as the next major areal-density inflection for HDDs.

Limits

Manufacturing complexity — laser writers, thermal control, and new media stacks increase integration risk (Seagate Mozaic technical articles).
Vendor concentration in shipping products — public 2026 announcements emphasize Seagate production; cross-vendor parity is not uniform (see Toshiba/Western Digital roadmap commentary in trade press).
Not a latency revolution — HAMR solves density; seek times and rotational latency remain mechanical.
Roadmap figures are vendor claims — capacity per drive and per-platter targets change with qualification timelines.

Typical fits

Hyperscale and cloud nearline tiers optimizing $/TB and watts/TB
Large sequential pools where HDD economics still beat flash
Deployments that can qualify new drive generations on a controlled schedule

Uncertainty notes

firstSeen "2024" follows Seagate’s statement that Mozaic 3+ Exos 30TB+ drives began shipping to cloud customers in Q1 calendar 2024 — vendor claim.
Mozaic 4+ up to 44TB and hyperscale qualification statements are from Seagate March 2026 press materials — vendor claim.

Sources

01Seagate — Heat Assisted Magnetic Recording (HAMR) · accessed 2026-10-06
02Seagate — What is Mozaic 3+? (HAMR platform overview) · accessed 2026-10-06
03Seagate — Mozaic 4+ qualified and in production (press release, March 2026) · accessed 2026-10-06
04Seagate — CMR/SMR list (Mozaic HAMR CMR capacity rows) · accessed 2026-10-06
05Seagate — Gen 2 plasmonic writer (Mozaic thermal write path) · accessed 2026-10-06