In short, solid state drives (SSDs) and regular hard disk drives (HDDs) store data differently. SSDs use flash memory chips to store data digitally while HDDs use magnetic disks to store data mechanically. This fundamental difference leads to significant performance advantages for SSDs over HDDs.
How do SSDs and HDDs differ in their physical construction?
SSDs consist solely of flash memory chips and a controller. Flash memory stores data in transistors that retain their on or off state even when power is removed. This is different from volatile RAM that loses its data when power is cut off.
Because they have no moving parts, SSDs are less prone to mechanical failure. SSDs are also much smaller and lighter than HDDs. However, flash memory cells have a limited lifespan and will eventually wear out after repeated write/erase cycles.
HDDs consist of one or more spinning magnetic disks called platters. These platters are coated with a magnetic recording material. A read/write head on an arm accesses data as the platters spin at high speed. HDDs also contain motors, electronic circuitry, and other mechanical components.
This complex mechanical construction makes HDDs bulkier and more prone to breakdowns. The moving parts consume more power compared to SSDs. HDD platters are also fragile and can be damaged by physical shocks.
How does data storage differ between SSDs and HDDs?
SSDs store data in memory cells made up of floating-gate transistors. These transistors can be electrically charged to store a 1 or 0 bit value. Data is stored in blocks containing thousands of cells.
To write new data, a block must be erased first before programming it. Erasing resets all cell values to 1. This process is called erase-before-write and is a key reason SSDs slow down as they fill up.
HDDs store data magnetically on the platter surface. The presence or absence of magnetism in a spot represents 1 or 0. New data can be directly written by changing the magnetism of a spot. There is no need to erase existing data first.
However, long term magnetic stability remains a challenge. HDDs can experience data loss over time as the magnetic domains destabilize. SSDs do not suffer from this problem.
What are the speed differences between SSDs and HDDs?
SSDs are much faster than HDDs at reading and writing data for several reasons:
- No moving parts – SSDs eliminate seek time for the head to move to data
- Lower access latency – data can be accessed directly and instantly
- Faster interface – SSDs use SATA/PCIe compared to HDDs’ SATA interface
Benchmarks show SSDs can achieve 500-550 MB/s sequential read/write speeds and up to 100,000 IOPS for random access. HDDs max out at around 200 MB/s transfer speed and 150 IOPS.
However, write speeds on SSDs slow down as more blocks fill up. Garbage collection to erase old blocks takes time and competes with new writes. HDD write speeds remain consistent regardless of disk usage.
What are the durability differences?
SSD endurance is measured in drive writes per day (DWPD). Mainstream consumer SSDs are typically rated for 0.3 to 1 DWPD for a 5 year lifespan. High-end models go up to 10 DWPD. This equals around 100GB to 300GB of data written per day.
Exceeding the rated DWPD will cause the drive to wear out quicker. However, light to moderate usage well within the DWPD rating should let an SSD last 5 or more years.
HDDs do not have a DWPD rating. But HDDs are considered more durable for heavy write workloads since they do not experience declining performance as they fill up.
Operating conditions also affect longevity. SSDs and HDDs can both wear out quicker in harsh environments with high temperatures, vibration, or shocks. SSDs are more resilient to physical shocks while HDDs are more prone to damage.
How do SSDs and HDDs compare for capacity?
HDDs are available in much larger capacities than SSDs. Typical capacities include:
| Drive Type | Capacities |
|---|---|
| HDD | 250GB to 18TB |
| SSD | 120GB to 8TB |
The highest capacity HDDs are over twice as large as the biggest SSDs. However, SSD capacities continue to grow rapidly as production costs decrease. A 16TB consumer SSD was recently unveiled by Micron.
For the average user, SATA SSDs up to 2TB and HDDs up to 6TB provide ample storage. Enthusiasts needing 10TB or more still require HDDs.
How do SSDs and HDDs compare on price?
HDDs are considerably cheaper per gigabyte compared to SSDs. A 1TB hard drive costs around $40 while a 1TB SATA SSD is around $80. High speed NVMe SSDs are even more expensive.
However, the price gap between HDDs and SSDs has shrunk over the years. The cost per GB for SSDs has plunged from around $2 in 2012 to under $0.10 now. HDD pricing has only fallen slightly in comparison.
With fewer moving parts, SSDs also help lower total cost of ownership through reduced power usage, cooling, and space requirements.
Which is better for gaming – SSD or HDD?
SSDs are strongly recommended over HDDs for gaming. Games have grown to occupy 50GB or more of storage space. Long loading times from slow HDDs can ruin the gaming experience.
Storing games on an SSD greatly speeds up boot times and load screens. Levels load in seconds rather than minutes. Games also benefit from faster texture and asset streaming from SSDs.
The downside is having enough room on costly SSDs for a large game library. A 1TB or 2TB SSD offers ample space for 10+ games. Otherwise, storing less frequently played games on HDDs is an option.
When should you use an HDD over SSD?
While SSDs are superior to HDDs in most usage scenarios, HDDs still have benefits making them suitable for certain use cases:
- Cold storage – HDDs work well as low cost cold storage for infrequently accessed data
- Backup drives – High capacity HDDs are ideal low cost storage for backups
- Bulk storage – Surveillance systems writing 24/7 rely on high capacity HDDs
- Budget conscious users – HDDs provide much more storage capacity per dollar spent
Gamers on a tight budget may use an SSD for their main system drive and couple it with a high capacity HDD to store games. Many desktop PCs also include both an SSD and an HDD to balance speed and storage capacity.
Conclusion
SSDs provide a massive speed boost over HDDs thanks to innovations like flash memory and lack of moving parts. HDDs cannot compete when it comes to performance. However, HDDs still win out on storage capacity and price per gigabyte.
For most users, an SSD provides the best overall experience as a boot drive. HDDs work well for bulk data storage at a lower cost. Gamers require SSDs for fast game load times but may store less frequently played titles on HDDs. With SSD pricing decreasing steadily, HDDs will likely be relegated to niche bulk storage uses in the future.