What is a hard disk drive?
A hard disk drive (HDD) is a type of computer storage device that uses magnetic storage to store and retrieve digital data. HDDs are non-volatile storage, meaning they retain data even when powered off. An HDD consists of one or more rigid platters coated with a magnetic material, and a read/write head that floats just above the platter surface on an air bearing. Data is written to the platters by orienting the magnetization of the material. To read data, the read head detects the magnetization of the material passing under it. HDDs have been the dominant form of high capacity, non-volatile storage since the 1960s. While solid state drives (SSDs) have been gradually displacing HDDs in some markets due to advantages in performance, power consumption, size and reliability, HDDs continue to hold cost and capacity advantages over SSDs in most applications.
Key characteristics of HDDs
– High capacity – Modern HDDs can store many terabytes (TB) of data. Capacities up to 16 TB for consumer HDDs and 18 TB for enterprise HDDs are currently available.
– Non-volatile storage – HDDs retain data even when powered off. This contrasts with volatile random access memory (RAM).
– Sequential access – HDDs are best suited for sequential data transfers, rather than random access.
– Magnetic recording – Data is stored and retrieved using magnetization of a magnetic material coating the platters.
– Movable read/write heads – The read/write heads float just above the platter surface during operation.
– Mechanical components – The use of spinning platters and moving heads introduces physical constraints on size, shock resistance, power consumption, noise and access times.
Types of HDDs
There are a few main types of HDDs:
– Desktop HDDs – Designed to be used in desktop computers and external enclosures. Typically 3.5 inches in diameter. Offer high capacity and low cost per gigabyte.
– Laptop HDDs – Smaller 2.5 inch and 1.8 inch HDDs designed for use in laptops. Balance capacity, performance, power consumption and physical size.
– Enterprise HDDs – Optimized for performance, reliability and high workload ratings in server and storage environments. Use advanced technologies like helium sealing.
– Surveillance HDDs – Designed for constant writing in security camera recording applications. Tuned for write intense workloads.
Do you need an HDD?
Whether you need an HDD depends on your storage needs and use case. Here are some questions to consider:
How much capacity do you need?
If you need terabytes of storage space on a budget, HDDs remain the most cost effective option per gigabyte. For mass storage of photos, videos, games and other media files, HDDs are likely the best fit. SSD costs drop steadily, but HDDs retain a substantial price per TB advantage. A 4 TB HDD can be purchased for around $100, while a 4 TB SSD still costs over $400.
What will you use the storage for?
HDDs excel at sequential data transfer. This makes them well suited for:
– Storing and playing back media like music, videos and photos
– Gaming storage
– Performing backups
– Archiving large amounts of data
But for applications requiring many small, random data accesses, SSDs are typically better thanks to much faster access times. This includes uses like:
– Operating system drive
– Program and application storage
– Caching and temporary files
A hybrid approach is common, with OS and programs on a SDD and large media collections on a HDD.
How reliable does the storage need to be?
SSDs are inherently more reliable than HDDs since they have no moving parts. HDDs are susceptible to damage or failure from:
– Physical shock – Dropping a HDD can damage internal components
– Vibration – The platters and head require stable positioning
– Magnetism – Magnetic fields can erase data from the platters
– Contamination – Dust can interfere with the head floating over the platter
So for mission critical data or environments prone to vibration, contamination or instability, SSDs are a safer bet. But HDD reliability continues to improve, with modern drives often lasting 5 years or more even with daily use. And HDDs have the advantage that data loss from failures is often recoverable, while SSD damage is more likely to be complete.
How much performance do you require?
SSD performance is far ahead of HDDs, due to the high latency of moving HDD heads and spinning up platters. Average HDD access times are in the 10-20ms range, while SSDs access data almost instantly. SSDs have bandwidth of 500-600 MB/s, compared to 100-200 MB/s for HDDs. So for very high performance needs, SSDs are required. But for many common workloads and use cases, HDD speeds are sufficient.
When are HDDs the best choice?
Here are some common situations where HDDs shine:
– **Bulk storage** – When you need terabytes of storage to archive media, documents, backups, etc. HDDs offer unbeatable storage density per dollar.
– **Gaming library** – A high capacity HDD can store dozens of large modern games, which typically range from 25 GB to over 100 GB each. Loading times will be slower than an SSD, but maximum capacity is the priority for a gaming library.
– **External storage** – External HDDs provide cheap, convenient storage that can be easily transported or shared between devices. Capacities up to 16 TB allow storing enormous media collections.
– **NAS devices** – Network attached storage devices commonly populated with multiple HDDs provide shared access to huge pools of storage. Reliability can be enhanced through RAID configurations.
– **Surveillance recording** – Constant writing of video surveillance footage is better handled by surveillance tuned HDDs rather than SSDs. High write endurance is critical.
– **Boot drives for secondary computers** – When performance needs are moderate, HDDs can serve as inexpensive boot drives for older systems. For your main computer, an SSD is still recommended for boot.
When are SSDs a better choice than HDDs?
SSDs outperform HDDs in these key areas:
– **OS & application drive** – The speed boost provided by an SSD is most impactful as the primary drive. Boot, loading and response times are vastly improved over even the fastest HDDs.
– **External portable storage** – External SSDs have less capacity than portable HDDs, but the durability, silence, speed, size and power efficiency make them better suited for on-the-go use.
– **Mission critical storage** – In environments where data integrity is paramount, SSD reliability and resilience makes them the storage media of choice over HDDs.
– **Servers & high performance workstations** – HDD bottlenecks are unacceptable in high performance computing environments, making SSDs the standard for maximizing storage throughput and access latency.
– **Noise & vibration sensitive applications** – The mechanical nature of HDDs generates noise and vibration, making SSDs better suited for use in sound recording, environments that require silence, or where vibration needs to be minimized.
– **Mobile computing** – The light weight, compact size, durability and power efficiency of SSDs are crucial advantages in laptops and other mobile devices where HDDs aren’t practical to use.
Key advantages of HDDs
HDDs have maintained their dominance over SSDs in specific areas:
Price per gigabyte
HDD – $0.02/GB (4TB for $100)
SSD – $0.20/GB (4TB for $400)
While SSD prices fall each year, HDDs continue to offer far lower cost per terabyte. For mass storage needs, HDDs provide the most storage capacity within a limited budget.
Maximum capacity
HDD – 16TB maximum for consumer models
SSD – 10TB max for consumer models
For storing truly vast quantities of data, HDDs are the only option. Data center and enterprise class HDDs scale even higher, up to 18TB per drive.
Rewritability and longevity
HDDs can withstand the rewrite of data hundreds of thousands or even millions of times on the same platter surfaces. SSDs gradually deteriorate after tens of thousands of writes to a given block of storage cells. HDDs have proven reliability over decades of consumer use.
Key advantages of SSDs
Where HDDs fall short, SSDs deliver huge benefits:
Performance
HDD – 100-200 MB/s sequential read/write speeds
SSD – 500-600 MB/s sequential read/write speeds
SSD speeds can reach into the gigabytes per second for high end drives on fast interfaces like PCIe. Access times are magnitudes faster than HDDs.
Shock and vibration resistance
HDDs rely on delicate mechanical components like drive heads floating barely off the platters on a cushion of air. Sudden shock or vibration can cause catastrophic failures. SSDs have no moving parts and are far more tolerant of harsh conditions.
Noise
HDDs require spinning platters and moving heads, producing noise that is audible to users during disk accesses. SSDs are completely silent as they have no physical moving parts.
Power efficiency
HDD motors consume power even while idling. SSDs only use power when data is actively being read or written. For mobile devices, SSDs extend battery life vs. HDDs.
Conclusion
While HDDs still dominate as the primary form of high capacity consumer storage, SSDs continue to grow in popularity and affordability. For many, a combination of a smaller SSD for OS, programs and high performance tasks paired with a larger HDD for media storage provides an ideal blend of speed, responsiveness and capacity.
In the consumer SSD vs. HDD decision, the key considerations are performance needs, capacity requirements, reliability concerns, power and noise profiles, form factors and budget. Applications requiring ultimate speed, ruggedness and power efficiency favor SSDs, while sheer capacity and cost efficiency remain the domains of the venerable HDD. Moving forward, expect HDD capacities and costs to remain low, and SSD prices to continue to close the gap as adoption increases. With their strengths combined, both HDD and SSDs look to remain vital storage technologies for the foreseeable future.