Hard drives and hard disks refer to devices that are used for digital data storage in computers and other devices. While the terms are sometimes used interchangeably, there are some notable differences between hard drives and hard disks.
A hard drive is the complete physical assembly that houses one or more hard disks along with the other components like controller, motors, etc. Hard disks on the other hand are the platters inside the hard drive that are coated with magnetic material to store data. So hard disks are essentially the storage media inside hard drives.
While hard drives and hard disks are closely related, they have differences when it comes to factors like capacity, speed, portability and more. This article will take a deeper look at the distinctions between these two common digital storage technologies.
Definition of a Hard Drive
A hard drive is a data storage device that contains one or more hard disks and the hardware that reads and writes to those disks. Hard drives are used to store digital information in computers, servers, smartphones, tablets, and other devices. The primary function of a hard drive is to store data permanently
According to Crucial, a hard drive consists of rapidly spinning platters coated in magnetic material paired with read/write heads that move back and forth to access data on the platters. All of this is encased in an air-sealed enclosure. The hard drive hardware controls how data is written to and read from the platters using electromagnetism. This allows the drive to store and retrieve digital data.
Hard drives enable long-term storage of large amounts of data. The capacity of a hard drive, which is measured in gigabyte (GB) or terabytes (TB), determines how much data it can hold. Common consumer hard drive sizes range from 250GB to 4TB for desktop models and 500GB to 2TB for notebooks.
Definition of a Hard Disk
A hard disk is a non-removable magnetic disk that stores digitally encoded data. It is a key component of a computer that allows the long-term storage and retrieval of data. Hard disks use platters coated with magnetic material to store data, with read/write heads that can magnetize or detect the magnetism of these platters in order to write or read data (Crucial.com, 2022). The platters rotate at high speeds while the read/write heads move back and forth across the platters to access different regions, allowing data to be written and read in a random-access manner. Hard disks are non-volatile storage, meaning they retain stored data even when powered off. They have high storage capacity compared to other storage media like solid state drives and are able to store large amounts of data like the operating system, applications, files and more on a computer.
Primary Difference
The main difference between a hard drive and a hard disk is that a hard drive refers to the complete physical unit or device that stores data, while a hard disk refers specifically to the disks inside the hard drive that actually store the data. In other words:
- A hard drive is the full assembly including the disks, motor, drive controller, and external hardware like casing and cables.
- A hard disk refers only to the platters inside the drive that are coated with magnetic material to store data.
So a hard disk is a key component inside the fully assembled storage device called a hard drive. The hard drive includes the hard disk plus additional supporting hardware and electronics that allow the disks to spin, read/write heads to access data, and connectors to interface with the computer.
To summarize, a hard disk is a internal component and the hard drive is the complete external storage unit.
Other Differences
There are several other notable differences between hard drives and hard disks beyond their primary difference in physical hardware vs logical interface:
- Portability – Hard drives are designed to be portable and removable, allowing you to take your data with you or transfer it between devices. Hard disks are fixed inside a computer and not designed for portability.
- Capacity – Hard disk capacity is limited by the physical size of the platters inside, typically ranging from 250GB to 4TB for consumer models. External hard drives can have much higher capacities since size is less limited, currently reaching up to 16TB.
- Access speed – Hard disks rely on physical spinning disks for access, giving them slower speeds than SSD hard drives which use flash memory. The fastest hard disks have 7200 RPM spindle speeds.
- Failure rates – The mechanical nature of hard disks leads to higher failure rates compared to solid state hard drives. Annual failure rates are estimated around 2-3% for consumer hard disks.
Overall hard disks have greater size and speed limitations compared to removable hard drives. But modern externals have largely caught up in speed while offering vastly higher portability.
Use Cases
Hard drives are traditionally used for mass storage in desktop computers and servers. Their high capacity and low cost make them well-suited for storing large amounts of data that does not need fast access speeds. Common applications for hard drives include storing operating systems, programs, documents, media files, and backup data. They are the primary type of long-term data storage in most computers.
Hard disks excel at sequential data transfer, which makes them effective for storing and retrieving large files in order. This makes them ideal for workloads like media streaming, gaming, scientific data analysis, and database applications. Hard drives are still the most cost-effective solution for increasing a device’s storage capacity.
SSDs are better suited for applications requiring quick access to data and fast boot times. Their superior random read/write performance delivers much lower latency and higher input/output operations per second. This speed advantage makes SSDs the preferred choice for primary storage in laptops, high-performance desktops, and servers needing fast data access. Common SSD applications include booting operating systems, loading programs, launching applications, opening files, and running games.
SSDs are also preferable for read-intensive applications like boot drives, web servers, real-time analytics, and scientific computing. Their lack of moving parts enables better reliability and resilience against shocks/vibrations compared to hard drives. However, SSDs are more expensive per gigabyte than HDDs. For cost-effective mass storage, HDDs still reign supreme.
In summary, hard drives are better for archival storage and large capacity at lower costs. SSDs excel at speed-sensitive tasks requiring fast random access. HDDs and SSDs are often used together in hybrid configurations, with SSDs handling primary storage and HDDs providing secondary storage.
Form Factors
Hard drives and hard disks come in a variety of physical sizes known as form factors. Some common form factors include:
- 3.5-inch – The most common desktop hard drive size, typically found in desktop computers. 3.5-inch hard drives are about 4 inches wide and 5.8 inches long (101.6 x 147 mm).
- 2.5-inch – The most common laptop hard drive size, typically found in laptops. 2.5-inch hard drives are about 2.75 inches wide and 3.96 inches long (69.85 x 100.2 mm).
- 1.8-inch – A smaller form factor used in some ultraportable laptops and devices. 1.8-inch hard drives are about 1.7 inches wide and 2.1 inches long (54 x 78 mm).
- mSATA – A miniaturized Serial ATA form factor commonly used in laptops, all-in-one PCs, and embedded systems. mSATA drives are about 1.8 inches long and 1 inch wide (50.8 x 29 mm).
- M.2 – A small form factor connector standard designed as a replacement for mSATA. M.2 drives come in several lengths, with common sizes being 30mm, 42mm, 60mm, 80mm, and 110mm.
The form factor impacts the physical size and interface connectors of the drive. Most desktop hard drives use 3.5-inch form factors with SATA interfaces, while most laptop drives use 2.5-inch form factors. Smaller devices may use mSATA, M.2, or other compact form factors.
References:
https://www.techtarget.com/searchstorage/definition/HDD-form-factor-hard-disk-drive-form-factor
https://en.wikipedia.org/wiki/List_of_disk_drive_form_factors
Failure Rates
Research shows that failure rates for hard drives and hard disks can vary substantially based on the specific model and manufacturer. However, some general trends emerge when comparing the two.
According to Backblaze, the annualized failure rate (AFR) for hard drives was 1.54% in Q1 2023. This was higher than previous quarters due to aging drives. Backblaze also reported the lifetime AFR for hard drives at 1.39% in Q2 2022.
Hard disks, specifically SSDs, tend to have lower failure rates than traditional hard drives. A 2021 Backblaze study found the AFR for SSDs was just 0.92%, much lower than hard drives.
The primary factors affecting failure rates are the moving parts in traditional hard drives. SSDs with no moving parts tend to be more reliable over time. Hard drives also seem prone to higher failure rates as they age over several years of use.
In summary, hard disks like SSDs generally have lower annual failure rates, often under 1%. Hard drives exhibit failure rates of 1-2% per year, increasing with age. So hard disks tend to last longer without failing compared to hard drives.
Pricing
There are considerable differences in the typical pricing of standalone hard disks compared to enclosed hard drives. According to AWS, SSD storage can cost $0.08–0.10 per GB, while HDD storage is much more affordable at just a fraction of that cost. This aligns with current market pricing shown on sites like Disk Prices, where internal HDD storage starts under $0.01 per GB for lower capacities.
For example, a 1TB internal 2.5″ HDD can be purchased for around $40, while a 1TB internal 2.5″ SSD is typically over $80. As capacity increases, HDDs remain the more cost-effective option with 10TB+ models coming in below $0.02 per GB. SSD pricing also improves at higher capacities but is still several times more expensive per GB compared to HDDs.
When looking at external portable drive enclosures, SSDs still command a premium price, often 2-4x higher than a traditional HDD. Considering the additional benefits of SSDs like performance, power efficiency, and ruggedness, the extra cost may be justified for some users. However, those prioritizing high capacities and affordability will find HDDs to be better value.
Conclusion
In summary, while the terms “hard drive” and “hard disk” are sometimes used interchangeably, there are some notable differences between the two. The main difference is that a hard drive refers specifically to the complete physical storage device that contains the read/write heads, platters, and controller. A hard disk refers only to the actual disk platters that store the data inside the drive enclosure.
Hard drives are finalized products sold to end users that can be easily installed in computers and storage systems. Hard disks are components that go into the manufacturing of hard drives and solid state drives. Hard disks have higher failure rates compared to SSDs, while hard drives are generally cheaper per gigabyte for higher storage capacities.
The choice between a hard drive vs an SSD depends on performance needs, storage capacity requirements, and budget. Hard drives are better suited for secondary storage and backups due to their lower cost. SSDs are preferable for applications requiring faster load times or read/write speeds thanks to their lack of moving parts.
