Conventional Magnetic Recording

CMR

Non-overlapping tracks on rotating platters—the default HDD write model for random I/O.

In one minute

CMR lays down magnetic tracks side by side without overlap. Modern drives still use perpendicular magnetic recording under the hood; vendors label the product behavior “CMR” to distinguish it from shingled (SMR) layouts.

If you grew up on hard drives, CMR is the mental model you already carry: each track is its own lane, and rewriting a sector does not require reshuffling neighboring tracks. That simplicity is why CMR remains the conservative choice for NAS boxes, RAID arrays, and any workload with unpredictable rewrites.

Areal density still climbs through tighter track pitch, better heads, and signal processing—but the recording topology stays “conventional.” When density pressure became painful, the industry split: keep CMR for general-purpose drives, and introduce SMR where sequential writes dominate.

High-capacity nearline lines now mix classic CMR, SMR, and newer heat-assisted (HAMR) or microwave-assisted (MAMR) variants. Reading a datasheet row that says “Recording Technology: CMR” is really asking: can I treat this like a normal random-write disk?

Compared to neighbors

SMR overlaps tracks like shingles, boosting density but changing rewrite paths. HAMR and MAMR attack the physics limit of smaller bit cells on CMR-class layouts rather than changing the shingle topology.

Strengths

Predictable random writes — non-overlapping tracks avoid the rewrite amplification and host-managed quirks that SMR can introduce.
Broad compatibility — Seagate positions CMR drives as plug-and-play across typical NAS, DAS, and server backplanes without SMR-specific zoning.
Mature ecosystem — decades of firmware, SMART telemetry, and recovery tooling target conventional track layouts.

Limits

Density ceiling vs SMR — CMR trades some areal density for simpler rewrite behavior.
Not a flash substitute — latency and IOPS remain bounded by spinning media and mechanical seeks.
Labeling varies by vendor — older manuals say “perpendicular recording” while newer sheets say “CMR”.

Typical fits

General-purpose desktop and NAS pools with mixed read/write
RAID or ZFS pools where rewrite amplification is costly
Boot/data disks when SMR host support is unknown
Archive tiers that still need occasional in-place updates

Uncertainty notes

Capacity figures and Mozaic HAMR rows on Seagate’s public list are vendor-published; cross-check before quoting exact TB SKUs.

Sources

01Seagate — CMR and SMR hard drive list · accessed 2026-10-06
02Seagate BarraCuda 3.5 HDD datasheet (CMR vs SMR by SKU) · accessed 2026-10-06
03Seagate SkyHawk CMR product manual — recording method row · accessed 2026-10-06
04Seagate Exos X24 SATA manual — perpendicular recording technology note · accessed 2026-10-06