Internal hard drives, ranked by cost per terabyte

An internal hard drive is the workhorse of bulk storage: a sealed mechanical disk that slots straight into a desktop tower, a NAS bay or a server backplane over a SATA cable. Because spinning platters store data far more cheaply than flash memory, internal HDDs deliver the lowest cost per terabyte of any mainstream storage you can buy — typically a small fraction of what an equivalent SSD costs per terabyte. That makes them the default choice for media libraries, backups, surveillance footage, NAS pools and any archive where capacity matters more than raw speed.

The specs that actually decide value are capacity, recording technology (CMR vs SMR), rotational speed (5,400–7,200 RPM), cache size, and the drive’s rated workload in terabytes written per year. NAS and surveillance models add vibration tolerance and firmware tuned for 24/7 arrays. As a rule, the sweet spot for $/TB sits in the high-capacity 12–20 TB range, where the cost of the drive’s mechanics is spread across the most platters. Smaller 1–4 TB drives almost always cost more per terabyte. Used and recertified enterprise-class drives can undercut new consumer models substantially — a sound option for secondary tiers if you keep proper backups.

3.5-inch vs 2.5-inch, and CMR vs SMR

Two choices shape almost every internal-HDD purchase: physical size and recording method. 3.5-inch drives dominate desktops and NAS units and reach the highest capacities and the lowest $/TB. 2.5-inch drives are thinner and lower-power but cap out far lower and cost more per terabyte. Separately, how the drive writes tracks — conventional (CMR) or shingled (SMR) — affects sustained-write and rebuild behaviour.

For anything that sees regular writes — a NAS, a RAID array, a video capture target — prefer 3.5-inch CMR. SMR is fine for write-once archival disks. Check our CMR vs SMR guide for how to identify which method a model uses before you buy.