How much hard drive you actually need

A hard drive is no longer the drive your system runs on. That job went to the SSD, which answers fast enough that the whole machine feels quicker for it. What a mechanical drive still does better than anything is hold a lot for a little, so size it for the pile you are moving off the fast drive, not for a machine you plan to run from it.

What a hard drive is for now

The split is between what you work from and what you keep. The operating system, your applications, and the files you have open want the SSD, because every one of those is read constantly and a delay in reading them is a delay you feel. A media library you play from, a photo archive you dip into, last year's projects, a backup you hope never to need — those are read occasionally, and the slower drive holding them costs a fraction per terabyte.

So the question is not whether a hard drive is fast enough to run a machine. It is not, and it does not need to be. The question is how much of the cold pile you have, and how fast that pile is growing.

Size for the pile you are moving off

Measure what you would actually put on it. Walk the fast drive and the external disks and the folders you have stopped importing to, and add up what is bulk rather than working data: the video, the raw photos, the game installs you rotate in and out, the archives you keep but rarely open. That total, plus the growth you can already see, is the drive you are sizing.

A backup is its own case, and it asks for more room than the data it protects. A backup worth keeping holds more than one copy in time, so that a file deleted or corrupted last week can still be recovered from the week before. That history is the point of it, and it wants headroom the size of the source several times over, not once.

One larger drive is usually cheaper per terabyte than two smaller ones, up to the top of a range, where the newest and densest drive carries a premium for being the hardest to build — the same arithmetic as any storage. Divide each price by its capacity and compare before you assume the biggest is the best value.

Why a cheap large drive can be slow

Two drives at the same capacity and a very different price are usually two different ways of writing the platter. The cheaper one is often SMR, shingled magnetic recording, which overlaps its tracks like roof tiles to fit more data on the same disk. The catch is in rewriting: because the tracks overlap, changing data in one means re-laying the whole band around it, so sustained or random writes slow sharply once the drive's small fast buffer fills. The dearer one is CMR, which writes each track on its own and keeps a steady write speed.

That difference decides what a drive is good for, not whether it is good. SMR is fine for what a hard drive mostly does — written once in long runs, read many times after: a media library, a cold archive, a disk you fill and leave. It is poor at exactly the jobs that write and rewrite constantly: a backup target taking daily changes, or a drive rebuilding into a NAS array, where the slowdown can stretch a job from hours into days. Manufacturers do not always print which one a drive is, and an unusually low price per terabyte is often the tell. It is worth knowing before you buy, because it is not something the capacity number shows.

What RPM and cache do, and do not

A drive's spin speed — commonly 5400 or 7200 RPM — and its cache set how quickly it reaches data and how well it absorbs bursts. Faster is better on both, but the gap between them is small next to the gap to an SSD, and on a drive you read occasionally it is smaller still. For a bulk drive, capacity and cost per terabyte decide the purchase; paying up for the faster spin on a disk that mostly sits and stores is spending on a number you will rarely feel. Where the spin speed earns its premium is a drive being actively worked — edited from, or serving several readers at once — which is a different drive from the one this guide is about.

How we track a drive's capacities

A drive sold at several capacities is one product with several sizes here, not several unrelated products. Each size is tracked on its own, with its own current price and its own price history. The sizes move independently — a run on 8 TB drives does not touch what 4 TB sells for — so folding them into one figure would misprice every one of them.

The drive's own page is where the sizes separate. The price that leads the page is the cheapest size currently tracked; below it, each size is listed with its own price, and the chart draws one line per size. Decide the capacity you are sizing for before you read the price.

Every hard drive in our catalog is on one page.