Solid state drives (SSDs) and hard disk drives (HDDs) are two of the most common types of storage devices used in computers today. Both have their own advantages and disadvantages when it comes to factors like speed, capacity, durability and cost. But when it comes to raw speed, SSDs are much faster than HDDs.
What is a SSD?
A solid state drive (SSD) is a type of storage device that uses flash memory to store data persistently. Unlike a traditional hard disk drive (HDD), a SSD has no moving mechanical components. Data is stored in microchips rather than on magnetic platters like on a HDD. This gives SSDs some key advantages over HDDs:
- Faster read/write speeds – SSDs can read and write data very quickly thanks to direct access to stored data on the flash memory chips.
- Lower latency – No moving parts means no seek time for the read/write heads, which gives SSDs much lower access latency.
- Better durability – With no moving parts, SSDs are less prone to damage or failure from shock, vibration, etc.
- Completely silent operation – No noise from spinning platters or moving heads.
- Lower power consumption – SSDs are more energy efficient than HDDs.
The lack of moving parts gives SSDs a big speed advantage over traditional HDDs. But SSDs also have downsides like lower capacities and higher costs per gigabyte compared to HDDs.
What is a hard disk drive (HDD)?
A hard disk drive (HDD) is a traditional storage device that uses magnetic storage to store and retrieve digital data. It stores data on quickly rotating platters coated with magnetic material. A read/write head flies just above each platter to read or write data as the platters spin:
- Data is accessed by moving the heads to the correct location on the drive platters.
- Heads can move to different positions while the platters spin.
- The platters spin at speeds typically between 5,400 RPM to 15,000 RPM.
HDDs have much higher capacities than SSDs today, with consumer models upwards of 10TB. But the moving parts introduce mechanical limitations compared to SSDs. The physical read/write heads are limited in speed and require time to move into position.
Comparing SSD and HDD speeds
When comparing the speeds of SSDs and HDDs, there are several metrics to consider:
- Sequential read/write speed – The maximum sequential throughput reading or writing large contiguous blocks of data.
- Random read/write speed – The speed reading or writing small, random blocks of data.
- Latency – The time required to initiate a read or write operation.
Sequential read/write speeds
For large sequential transfers, SATA SSDs can have read/write speeds of around 500-550 MB/s, while HDDs max out at around 100-200 MB/s. High performance NVMe SSDs can reach sequential read/write speeds over 3,000 MB/s.
| Storage Type | Interface | Sequential Read | Sequential Write |
|---|---|---|---|
| HDD (7200 RPM) | SATA 3 | 100-200 MB/s | 100-200 MB/s |
| SATA SSD | SATA 3 | 500-550 MB/s | 500-550 MB/s |
| NVMe SSD | PCIe 3.0 x4 | 3,000-3,500 MB/s | 2,000-2,500 MB/s |
For large sequential reads or writes, SSDs can be up to 5-10x faster than HDDs. The faster interface and lack of mechanical moving parts give SSDs their edge.
Random read/write speeds
For random access, SSDs really shine compared to HDDs. While HDD random read/write speeds typically max out below 1 MB/s, SATA SSDs can handle 30-100 MB/s for 4K random operations. Top NVMe SSDs exceed 1,000 MB/s for random reads and writes.
| Storage Type | 4K Random Read | 4K Random Write |
|---|---|---|
| HDD (7200 RPM) | 0.5-1 MB/s | 0.5-1 MB/s |
| SATA SSD | 30-100 MB/s | 50-90 MB/s |
| NVMe SSD | 250-600 MB/s | 200-400 MB/s |
For random access, SSDs provide up to 100x faster read/write speeds compared to HDDs. Avoiding the need to physically move heads makes SSDs tremendously faster for small random IO.
Access latency
Access latency measures the delay or time it takes for a storage device to start reading or writing data. HDDs have much higher latencies due to the need to move the physical heads, while SSD latencies are near instantaneous:
| Storage Type | Read Latency | Write Latency |
|---|---|---|
| HDD (7200 RPM) | 5-10 ms | 5-10 ms |
| SATA SSD | 0.02 ms | 0.2 ms |
| NVMe SSD | 0.015 ms | 0.1 ms |
SSD latencies are sub-millisecond, while HDD latencies are in the range of single digit milliseconds. This makes SSDs feel much more responsive for things like booting an operating system or loading applications.
Real-world performance differences
Synthetic benchmarks provide a glimpse into the raw speed differences, but how do SSDs and HDDs compare in real world consumer use cases? Here are some examples:
Boot times
Using an SSD can significantly reduce OS boot times compared to a HDD. Windows boot time can be cut from 30-90 seconds with a HDD down to 10-25 seconds with a SATA SSD. And NVMe SSDs can boot Windows in sub-10 second times.
Game/app loading
Games and applications load much faster from an SSD compared to a HDD. Level load times in games can be cut from 20-40 seconds on a HDD down to 5-15 seconds on a SATA SSD. NVMe SSDs drop load times even further to 1-5 seconds.
File transfers
Transferring files like photos, videos, ISO files, etc can take 2-3x longer on a mechanical HDD compared to SSD. Large sequential file transfers reach maximum interface speeds on both HDDs and SSDs. But SSDs maintain high speeds with small random transfers while HDD performance suffers.
Video editing
When editing and working with large video files, source material will load faster on SSDs while scratch disks will accelerate project render times. This improves workflow productivity and efficiency compared to solely using HDDs.
When do HDDs make more sense than SSDs?
SSDs are much faster, but HDDs have use cases where they still excel over SSDs:
- Cold storage/archival – HDDs better for infrequently accessed data due to lower cost per GB.
- Bulk storage – For terabytes of storage, HDD arrays are more cost effective.
- Write-intensive workloads – HDDs sustain higher continuous write workloads than early SSDs.
- Hot swappability – HDDs can be easily hot swapped without loss of data.
The introduction of new technologies like QLC NAND flash with higher endurance and capacities up to 16TB narrow the gap with HDDs. But HDDs still have advantages for high capacity bulk storage use cases.
SSD vs HDD: Quick Takeaways
- SSDs have no moving parts, resulting in faster speeds, lower latencies, and greater resilience against physical shocks/vibration.
- HDDs use moving platters and heads, limiting speeds but providing much higher storage capacities.
- SSD sequential read speeds exceed 500 MB/s and NVMe SSDs surpass 3,000 MB/s, compared to 100-200 MB/s max on HDDs.
- SSD random read/write performance is up to 100x faster than HDDs.
- SSD access latencies are in the microsecond range, while HDD latencies are in the millisecond range.
- Real world use cases like boot times, game/app load times, and file transfers are significantly faster on SSDs.
- HDDs are still preferred for some use cases like cold storage and bulk storage servers due to higher capacities and lower cost per gigabyte.
Conclusion
SSDs provide tremendous improvements in speed and performance compared to hard disk drives. The gap has narrowed with new SSD technologies that close the capacity difference while boosting endurance. For uses cases focused on speed like booting an OS, loading applications, transferring files, and running intensive workloads, SSDs are the clear choice. Their physical advantages of no moving parts also makes them more durable and shock-resistant than traditional HDDs. While HDDs are still useful for bulk storage needs, SSDs have become the standard for client and consumer storage requiring performance.