A hard disk drive (HDD) is a computer storage device that contains one or more hard disks inside for storing and retrieving digital data. The purpose of a hard drive is to store large amounts of data including the operating system, software programs, and user files on a permanent basis, even when the computer is turned off. Hard drives allow computers to have fast access to data as well as large storage capacities compared to other forms of storage like solid state drives or removable media (Source). The platter inside the hard drive spins at high speeds and the read/write head flies above it to read or write data onto the disk. Hard drives are considered non-volatile storage, meaning the data persists even when the drive has no power. Overall, the main role of a hard drive is to store and access large amounts of digital information reliably for computer systems.
HDD vs SSD
HDD stands for hard disk drive, while SSD stands for solid-state drive. Both are data storage devices used in computers, but they have some key differences.
In terms of storage capacity, there is not much difference between HDDs and SSDs. Both are available in capacities ranging from 128GB to 20TB or more (1). However, HDDs tend to offer more storage capacity per dollar compared to SSDs. It’s common to find 500GB to 1TB HDDs, while SSDs in the 64GB to 512GB range are more typical.
When it comes to speed, SSDs are much faster, with typical read/write speeds of around 500-550 MB/s compared to HDDs which average 80-160MB/s (2). This makes a noticeable difference in performance – programs and files load much quicker on an SSD.
SSDs are also lighter than HDDs because they don’t contain moving parts. This makes them better suited for portable devices. Additionally, SSDs are more durable because they are less susceptible to damage from drops or bumps.
The tradeoff is that SSDs have a higher cost per gigabyte compared to HDDs. You can get a 1TB HDD for around $40-50 while a 1TB SSD costs around $100-150 (1,3). So while SSDs are faster and more portable, HDDs allow you to get more storage capacity for your money.
Sources:
(1) https://www.avast.com/c-ssd-vs-hdd
(2) https://www.crucial.com/articles/about-ssd/ssd-vs-hdd
(3) https://www.diffen.com/difference/HDD_vs_SSD
HDD Storage Capacity
HDD storage capacity is measured in gigabytes (GB) or terabytes (TB). One terabyte is equal to 1,000 gigabytes.
The storage capacity of HDDs has increased dramatically over the years. In 1956, the first HDD held just 5MB of data. By the late 1990s, HDD capacities reached around 10GB. In the early 2000s, consumer HDDs reached around 120-160GB. In 2005, the first 1TB HDD was introduced.
Today, common HDD capacities for desktop computers include 1TB, 2TB, 4TB, 6TB, 8TB, 10TB, 12TB, 14TB, 16TB, 18TB, and 20TB. The highest capacity 3.5″ HDD currently available is 20TB (Horizon, 2023). However, HDD manufacturers like Seagate and Western Digital have roadmaps to develop even higher capacity HDDs up to 50TB in the coming years.
While HDD capacities have increased dramatically, the physical size of the drives has not. Higher capacity HDDs are achieved through greater areal density, meaning more bits can be stored in the same amount of disk space.
SSD Storage Capacity
SSD capacity is measured in gigabytes (GB) or terabytes (TB). SSDs use NAND flash memory to store data, which is different from the magnetic disks used in HDDs. The maximum capacity depends on the number of NAND flash chips on the SSD.
Currently, the largest consumer SSD is around 8TB for the M.2 form factor and 16TB for U.2 drives. On the enterprise side, the maximum capacity reaches up to 100TB for some newly released models like the Nimbus ExaDrive DC100. However, most average consumer SSDs max out between 1TB to 4TB.
SSD capacities have increased rapidly over the years as NAND flash memory density improves. The maximum capacity doubles approximately every 3 years. So we can expect to see consumer SSDs reach 16TB+ in the next few years.
Cost Comparison
When comparing the cost per gigabyte (GB) of hard disk drives (HDDs) versus solid state drives (SSDs), HDDs are generally much cheaper per GB. According to Disk Prices, consumer HDDs in early 2023 range from around $0.004 per GB for high capacity models up to $1.37 per GB for lower capacity drives. In contrast, consumer SSDs range from around $0.15 per GB for budget drives up to over $1 per GB for high performance models.
For example, a 16TB Seagate Exos HDD is around $0.004 per GB while a 2TB Samsung 870 QVO SSD is around $0.10 per GB. So the HDD offers 4000x more storage capacity per dollar spent. However, SSD prices have been dropping steadily over time while HDD prices have remained fairly flat. According to Backblaze, HDD prices have hovered around $0.02 per GB for the past decade but could reach $0.01 per GB soon.
Speed Comparison
SSDs are significantly faster than HDDs when it comes to read/write speeds. HDDs rely on spinning disks and moving heads to store and retrieve data, which has physical limitations. In contrast, SSDs use flash memory and have no moving parts, allowing for faster access.
For sequential read/write performance, a typical SATA SSD will have transfer speeds around 500-550 MB/s (megabytes per second), while a HDD maxes out below 200 MB/s. Comparing random access speeds, SSDs again are 10 times faster at around 100K IOPS versus 10-12K IOPS for HDDs. Even the slowest SATA SSD can deliver hundreds of megabytes per second while the fastest HDD hardly goes above 200 MB/s.(1)
NVMe SSDs connected over PCIe bring even faster potential speeds, ranging from 1,500 MB/s up to 3,500 MB/s for premium models. Top-end NVMe drives can hit nearly 1 million IOPS. So for tasks like booting an OS, loading games, or working with large files, SSDs provide a dramatic advantage over HDDs when it comes to transfer speeds.
Reliability
SSDs tend to be more reliable and durable than traditional HDDs according to research by cloud storage provider Backblaze. In their study of over 100,000 drives, they found SSDs had a failure rate of 1.5% over 4 years compared to 6.2% for HDDs over the same period [1]. The lack of moving parts in SSDs contributes to their improved reliability.
However, HDD reliability has improved over the years as well. One HDD from Western Digital had a mean time between failures (MTBF) of 2.5 million hours compared to 1.5 million hours for a Samsung SSD [2]. So while SSDs still tend to edge out HDDs in reliability tests, modern HDDs have very respectable MTBF ratings.
For most mainstream home and office use, both SSDs and HDDs are sufficiently reliable. But for mission-critical applications demanding maximum uptime, SSDs tend to be the safer choice currently.
Form Factors
HDDs and SSDs come in different physical form factors and sizes. The most common HDD form factors are 3.5″ and 2.5″ while SSDs come in 2.5″, M.2, and mSATA form factors.
3.5″ HDDs are the largest and are mostly used in desktop PCs while 2.5″ HDDs are smaller and used mainly in laptops. The larger 3.5″ HDDs allow for more platters and heads which enables higher storage capacities. Common 3.5″ HDD sizes range from 250GB to 10TB while 2.5″ HDDs range from 250GB to 2TB. [1]
2.5″ SSDs are the same dimensions as 2.5″ HDDs and are used to replace HDDs in laptops. However, SSDs like M.2 and mSATA are smaller and optimized to save space in compact devices. M.2 SSDs are about the size of a stick of gum and mSATA SSDs are about the size of a postage stamp. The smaller form factors allow SSDs to be used in ultra-thin laptops and tablets. [2]
So while HDDs offer larger 3.5″ form factors for maximum capacity, SSDs come in much smaller sizes that are optimal for portable devices where space is limited.
Use Cases
When choosing between an HDD and SSD, it’s important to consider the use case. HDDs tend to be better suited for secondary storage and backups due to their larger capacities and lower cost per gigabyte. SSDs, on the other hand, are better for applications that require faster read/write speeds thanks to their lack of moving parts.
According to AWS, HDDs are ideal for “data archiving, backups, and other write-once, read-many workloads.” The lower cost per GB makes HDDs a budget-friendly option for storing large amounts of infrequently accessed data like media files, documents, etc.
SSDs excel at use cases like boot drives, gaming, and running demanding applications. Their higher performance reduces boot times and load times within games and programs. SSDs are especially beneficial for read-intensive workloads since they can access data almost instantly.
Overall, if your priority is large storage capacity at a low cost, HDDs are likely the better choice. But for optimal speed and responsiveness, SSDs are superior, albeit at a higher price point. Consider your specific needs and workload patterns when deciding between HDD vs SSD.
Conclusion
In summary, when comparing hard disk drives (HDDs) and solid state drives (SSDs) in terms of storage capacity, cost, speed, reliability, and use cases, there are advantages and disadvantages to both. HDDs generally offer more storage capacity for less money, while SSDs are faster, more reliable, and better suited for portable devices. However, HDD capacities and speeds continue to improve while SSD prices continue to decline. For most general computing uses, an HDD or a hybrid HDD/SSD configuration provides a good balance of capacity, performance and cost. For tasks that demand faster access like gaming or running intensive software, SSDs are the ideal choice.
When deciding between an HDD or SSD, consider your budget, performance needs, and use case. HDDs are better for budget builds focused on storage capacity. SSDs are recommended for performance-driven builds where speed is essential. For a versatile option, use an SSD for your operating system and main applications, paired with an HDD for documents and media files. With the right combination chosen for your specific needs, you can build a PC that maximizes both speed and storage capacity.