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An HDD (hard disk drive) is non-volatile storage: it keeps data when power is off by recording it magnetically on spinning rigid disks called platters. HDDs remain useful for adding capacity, storing large files, and keeping a separate backup copy. Whether one is right for you depends on your device, storage needs, portability, and performance requirements.
How an HDD stores data
Inside a hard disk drive, one or more platters spin while an actuator positions read/write heads over the places where data is recorded. The heads read and write magnetic changes on the platters. Because the drive uses moving mechanical parts, it works differently from a solid-state drive (SSD), which stores data in flash memory and has no spinning platters. “Non-volatile” means data is retained without power; it does not mean a drive cannot fail or lose data.
Internal and external HDDs
Internal HDDs
An internal HDD is installed inside a computer to add storage or replace an existing drive. Compatibility is not universal: check that the computer has a suitable bay and supports the drive’s form factor, physical dimensions, and interface before buying. Seagate’s Internal Hard Drives page is a product reference, but the computer manufacturer’s documentation should guide compatibility decisions.
External HDDs
An external HDD connects to a computer or console, typically for portable storage, moving files, or keeping a backup. Check the device’s available port, the drive’s connection type, intended device support, and whether the drive needs separate power. Product specifications and compatibility vary by model, so consult the individual listing and your device documentation; Seagate’s Buy External Hard Drives (Data Storage) page shows one range of products.
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HDD or SSD: which suits the job?
Neither type is best for every use. Seagate describes HDDs as useful for high-capacity storage and SSDs as a fit for tasks that need higher performance. Consider what you will store and how quickly you need to access it: an HDD may suit a large media collection or backup, while an SSD may be preferable when performance is the priority. Compare the specific drive and device rather than assuming the technology alone determines the result. See Seagate’s Hard Drives and SSDs overview.
What to compare before choosing an HDD
- Capacity: Estimate the space your files and applications need, with room for growth. A smaller portable drive may suit file transfer or a limited backup set; a larger desktop drive may suit a large media library or whole-computer backup. Actual capacity needs depend on file sizes and how you use your devices.
- Reported capacity: The usable capacity shown by a computer may differ from the number printed on the drive. Seagate explains that manufacturers use decimal units—one gigabyte is one billion bytes—and that formatting and the operating environment affect accessible or reported capacity. Treat the displayed figure as an expected difference, not necessarily missing space.
- Portability and power: For an external drive, decide whether you need to carry it or leave it connected. Check the connection and power requirements for the particular model and device.
- Compatibility: For an internal drive, verify the bay or form factor, dimensions, interface, and system support. For an external one, verify the port, connection type, and device support.
- Performance: Rotational speed (RPM) is one factor in how quickly an HDD can find files, but it is not a complete measure of performance. Seagate’s consumer guide says a 7,200-RPM drive is faster than a 5,400-RPM drive, while noting that practical differences depend on use, file size, and whether the drive is external. Choose for the workload rather than RPM alone. See Everything You Want to Know About Hard Drives.
Using an external HDD for backup
An external HDD can hold a backup if it contains a separate copy of important files. Seagate defines the purpose of a backup as avoiding data loss by keeping important data in a second physical location. Copying files to another drive and then deleting the originals does not leave a backup; it leaves one copy. Seagate also cautions that RAID alone is not a self-contained backup. See its support article, “What is a backup?”.
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