US How SSDs and HDDs store data
An HDD, or hard disk drive, stores data as magnetic patterns on one or more platters that spin at typically 5,400 to 7,200 rpm. A read/write head on an actuator arm floats a few nanometres above the surface and moves across it to find each track. An SSD, or solid-state drive, stores data as electrical charge in NAND flash cells and has no moving parts at all.
That one difference explains most of the comparison. A hard drive is a precision mechanical device, so its speed is limited by how fast the arm moves and the platter turns, and its reliability depends on keeping the head and platter apart. An SSD is limited by its controller and interface, and its main wear mechanism is the slow ageing of the flash cells as they are rewritten.
SSD vs HDD compared
The figures below are typical for current 2.5-inch and 3.5-inch hard drives and for SATA and NVMe SSDs. Datasheets vary, so check the exact model before relying on a number.
| Property | SSD | HDD |
|---|---|---|
| Random access time | Around 0.1 ms or less | Around 5 to 15 ms |
| Sequential read | Around 550 MB/s (SATA) to 7 GB/s or more (NVMe) | Around 150 to 280 MB/s |
| Random IOPS | Tens of thousands to over a million | Around 100 to 200 |
| Operating shock | Typically around 1,500 G | Typically tens to a few hundred G |
| Operating temperature | 0 to 70 °C, or −40 to 85 °C for industrial drives | Typically 0 or 5 to 55 or 60 °C |
| Altitude | Not affected | Air-filled drives typically rated to around 3,000 m |
| Noise | Silent | Spindle hum and seek noise |
| Cost per terabyte | Higher | Lower, especially above 8 TB |
The gap in random performance is the one users notice. Booting, loading applications and running a database all involve thousands of small reads scattered across the drive, which is exactly what IOPS measures and where a hard drive is slowest.
Vibration, shock and temperature
For industrial and mobile systems, the environmental rows of that table matter more than speed. A hard drive’s head flies so close to the platter that a sharp knock while it is writing can make it touch the surface, and steady vibration pushes the head off track, so the drive retries and slows down. In a chassis with several drives, the drives even shake each other, which is why enterprise hard drives carry rotational vibration sensors.
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Vehicles and mobile machines. Road shock, engine vibration and constant movement favor SSDs, which are the usual choice for in-vehicle computers.
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Heat and cold. Most hard drives are rated for a narrow operating band and need warming before they spin up in the cold. Industrial SSDs are qualified across the industrial temperature range, typically −40 to 85 °C.
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Height above sea level. Air-filled hard drives rely on a cushion of air under the head, so they have an altitude limit. That matters for airborne systems and high mountain sites.
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Sealed, fanless enclosures. An SSD draws less power and gives off less heat, which helps when the only cooling is the case itself.
Endurance and data retention
The two drive types wear out in different ways. An SSD’s flash survives a limited number of program/erase cycles, so its endurance is quoted in terabytes written (TBW) and depends on the flash type: TLC and pSLC drives last far longer than QLC SSDs under heavy writes. A hard drive’s platters do not wear from writing, but its bearings, motor and heads age, so it carries a workload rating in terabytes per year and an annual failure rate.
Retention when the power is off also differs. JEDEC’s JESD218 standard expects a client SSD at the end of its rated life to hold data for a year unpowered at 30 °C, and an enterprise SSD for three months at 40 °C. A new SSD holds data far longer than that, but neither type should be treated as an archive left on a shelf for a decade.
When an HDD still makes sense
Hard drives are no longer the default boot drive, but they still earn a place where capacity matters most and the system sits still. Video retention is the clearest example: industrial NVRs that keep weeks of multi-camera footage often pair an SSD for the operating system with surveillance-rated hard drives for recording, because those drives are built for continuous writes at a lower cost per terabyte.
The same split works in edge servers and archives: an SSD for the operating system, databases and anything that is read randomly, and hard drives for large sequential files that are written once and kept. Where the system moves, gets hot or cannot be serviced easily, choose solid state throughout.
Quick answers on SSD vs HDD
SSD vs HDD: common questions
What is a hard drive?
A storage drive that records data magnetically on spinning platters. HDD is short for hard disk drive. It keeps files and the operating system with the power off and is read by a head on a moving arm.
What does a hard drive do?
It stores data permanently. The hard drive, or its modern replacement the SSD, holds everything that must survive a restart: the operating system, programs and files. RAM only holds what is in use.
Is an SSD faster than an HDD?
Yes, by a wide margin. A SATA SSD reads sequentially two to three times faster and finds random data around a hundred times faster. An NVMe SSD widens the gap further.
Can a computer use both an SSD and an HDD?
Yes. A common layout is an SSD for the operating system and applications and a hard drive for bulk data, provided the board has the SATA ports and the case has the drive bays.
Which lasts longer, an SSD or an HDD?
It depends on the use. In vehicles, vibration and heat, an SSD usually lasts longer. Under very heavy continuous writes, check the SSD’s TBW rating against the data you write each day.
We choose the storage for every system we supply as standard, matching SSDs, hard drives or both to the workload, capacity and environment, then image and validate the system before it ships.