An SSD (solid-state drive) stores data electronically in flash memory, whereas an HDD (hard disk drive) stores data magnetically on rotating platters. SSDs are generally faster, quieter, more durable, and more energy-efficient, while HDDs usually provide more storage for the same price.
Both devices are forms of secondary storage. They are non-volatile, meaning stored data remains available when electrical power is removed.
An HDD contains magnetic platters that rotate at high speed. An actuator moves a read/write head to the correct track and sector. Its access time includes seek time, while the head moves, and rotational latency, while the required sector rotates into position.
An SSD has no moving mechanical components. It stores bits using electrical charge in NAND flash memory cells, while a controller manages reading, writing, and the physical location of data. This gives an SSD lower access latency, especially when retrieving data from many different locations.
| Factor | SSD | HDD |
|---|---|---|
| Storage mechanism | Electronic flash memory | Magnetic rotating platters |
| Access speed | Faster, with low latency | Slower because mechanical movement is required |
| Durability | More resistant to shock | Vulnerable to damage from impact while operating |
| Power and noise | Lower power use and silent operation | Higher power use, vibration, and audible noise |
| Cost per gigabyte | Usually higher | Usually lower |
| Typical advantage | Fast startup and application loading | Economical storage of large data volumes |
A common misconception is that an SSD is simply a faster type of HDD. It is not: the two technologies use fundamentally different storage mechanisms. SSD memory cells also have a limited number of write cycles, although controllers use techniques such as wear levelling to extend their useful life.
In an IB exam, a compare question requires similarities and differences. State that both are non-volatile secondary storage, then link each difference to its mechanism rather than merely asserting that one is “better.”
