The most common type of hard drive found in computers today is the hard disk drive (HDD). HDDs have been around for decades and continue to be the storage device of choice for most desktop and laptop PCs. There are other types of drives available, like solid-state drives (SSDs), but HDDs remain the most widely used due to their lower cost per gigabyte and high capacities.
What is a Hard Disk Drive (HDD)?
A hard disk drive contains one or more rigid platters coated with magnetic material. These platters spin at high speeds while a read/write head floats just above the surface to access data. Data is stored magnetically in binary code across the platters in concentric tracks. When data is written, the head polarizes tiny magnetic domains on the platter surface. When data is read, the head detects the polarization of the domains to translate it back into binary.
HDDs record data mechanically with moving parts, making them the traditional magnetic storage device in computers. The main components of an HDD include:
- Platters – The disks that store data magnetically. At least one platter is required, but HDDs normally have multiple platters to increase capacity.
- Spindle – The central rod that rotates the platters.
- Read/write arm – The mechanical arm with a read/write head that moves across the platters to access data.
- Actuator – The mechanism that moves the read/write arm.
- Head – The small device on the read/write arm that reads and writes data as it moves over the platter surface.
HDDs are non-volatile storage, meaning they retain data even when powered off. They offer relatively inexpensive storage space and capacity compared to SSDs. HDD capacities range from a few hundred GB for portable drives up to 10+ TB for the latest high-capacity enterprise models. The platters spin at speeds between 5,400 and 15,000 RPM in consumer HDDs.
History of Hard Disk Drives
IBM introduced the first hard disk drive, the IBM 350, in 1956. It stood over 60 inches tall and weighed over a ton. The 350 stored 5 million characters (about 4.4MB) on fifty 24-inch platters. Access times were measured in thousandths of a second.
Throughout the 1960s and 1970s capacities steadily improved while prices dropped dramatically. HDDs started replacing reel-to-reel tape drives as the main storage device for computers, though they were still very large by today’s standards. By 1980, capacities reached upwards of 100MB.
The 1980s saw accelerating areal density, starting around 1 megabit per square inch and doubling annually. The 3.5-inch form factor debuted in 1983 and became popular in microcomputers. Drive capacities reached 20-40MB. Interface standards evolved from accessing HDDs through separate controllers to drive interfaces integrated on the motherboard.
areal density milestone was reached in 1991 with 1 gigabit per square inch. The same year, 2.5-inch HDDs entered the mobile computing market. Capacities of 80-340MB were common by the mid-1990s, with the first 1GB drive arriving in 1994. By the end of the decade, 17GB drives entered the enterprise space while 4-8GB drives were found in consumer PCs.
The 2000s brought exponential growth in HDD capacity through advances in technology like perpendicular recording and shingled magnetic recording. The 1 terabyte drive arrived in 2007, followed by 2TB in 2009. In the 2010s and beyond, capacities reached multiple terabytes on multiple platters with conventional recording. Helium filled drives provided efficiency improvements. SMR further increased areal density. Today’s consumer HDDs range from 1-5TB, with 10TB+ drives available for enterprise data centers.
Advantages of HDDs
Hard disk drives continue to be the most common type of storage in computers today for a number of reasons:
- Price per gigabyte – HDDs offer more storage capacity per dollar compared to SSDs. High capacity drives are affordable for consumers. This makes them ideal for bulk data storage needs.
- Established technology – First introduced in the 1950s, HDD tech is well proven and understood. Reliability has improved over decades of refinement.
- High capacities – With mature technology, HDDs can pack terabytes of storage space on multiple platters. The highest capacity HDDs top out above 10TB.
- Wide availability – HDD dominance means all computers support HDDs. Replacement and additional drives are easy to source.
- Technology refinements – Advancements like SMR boost capacity while innovations like helium reduce friction and power use, improving efficiency.
For general computing, gaming rigs, data storage servers, NAS devices, and other applications needing substantial, inexpensive drive space, HDDs cannot be beaten. Their combination of familiarity, capacity, and affordability means HDDs will continue to be the most common type of drive for the foreseeable future.
Disadvantages of HDDs
While HDDs excel when high capacity cheap storage is called for, they do have downsides that make other technologies preferable in some situations:
- Fragility – The mechanical nature of HDDs means they can suffer catastrophic failures from impacts, vibration, liquids, debris, etc. Data recovery is expensive.
- Noise – The spinning platters and moving heads create audible noise that can be distracting in quiet environments.
- Heat output – HDDs require more electricity than SSDs, producing more heat which requires cooling.
- Slower access – The moving parts limit data access speeds compared to pure electronic storage like SSDs.
- Larger size – The drive chassis and moving parts take up more physical space compared to compact SSDs.
While HDDs are suitable for most home and office uses, their limitations can make SSDs or other storage technologies preferable for things like portable devices, harsh environments, and mission-critical enterprise systems needing maximum speed.
Common HDD Form Factors
There are three common standard physical sizes, known as form factors, for hard disk drives as of 2023:
3.5-inch
The 3.5-inch form factor has been used in PCs since the 1980s. These drives are designed to mount in computer cases with a set of holes that match up with the holes on the bottom of the drive. They require both 5V and 12V power supplies. 3.5-inch HDDs offer the highest mainstream capacities of 4-5TB for a single drive, with 10TB+ for enterprise models. They are the most common type of HDD today due to their low cost per gigabyte and high capacities.
2.5-inch
Developed in the late 1980s for portable computers, 2.5-inch HDDs are smaller and use less power than 3.5-inch drives. They commonly appear in laptops, all-in-one desktop PCs, game consoles, and external hard drives. 2.5-inch drives max out around 2TB currently. While capacities are lower than 3.5-inch drives, the smaller size and power efficiency make 2.5-inch HDDs preferable for portable devices.
1.8-inch
Extremely small 1.8-inch HDDs were introduced in the late 1990s for early portable MP3 players. They max out around 500GB but have been largely superseded by flash storage in consumer devices. Some industrial applications still use 1.8-inch drives where a compact HDD is required.
Enterprise HDDs outside the standard form factors are also produced, like 1-inch microdrives. But for mainstream computing, 3.5-inch and 2.5-inch are by far the most common HDD sizes in use today.
HDD Interface Types
The interface connects the HDD to the computer. It carries power as well as data between the drive and system. There are several common hard drive interface types:
PATA
Parallel ATA, also known as IDE, is an early ribbon cable interface that was ubiquitous in PCs into the late 1990s and early 2000s. The parallel data transfer hits a maximum speed of 133 MB/s. PATA drives are obsolete today, having been replaced completely by SATA.
SATA
Serial ATA is now the most common HDD interface, used by 3.5-inch and 2.5-inch drives over the last decade. A single SATA cable connects the drive rather than the wide ribbon cable of older PATA/IDE drives. SATA interfaces transfer data serially rather than in parallel. Maximum speeds range from 150 MB/s for SATA 1.0 to 16 Gb/s for the latest SATA 3.3 specification.
SAS
Serial attached SCSI drives provide an enterprise interface designed for RAID arrays, servers, and storage systems where high reliability and performance are crucial. SAS HDDs are typically found in data centers but rarely in home computers. SAS offers duplex transfer up to 12 Gb/s.
USB
External portable hard disk drives use USB to interface with computers for data transfer. Most 2.5-inch HDDs in external enclosures connect via USB 2.0, USB 3.0, or USB 3.1 interfaces. While convenient for portable drives, USB HDDs are slower than internal SATA HDDs.
Network-attached storage devices may present internal SATA HDDs over Ethernet networks using protocols like SMB/CIFS or NFS to allow shared access from multiple computers.
Internal vs External Hard Drives
Internal HDDs mount directly inside desktop and laptop PCs to store the operating system and files. They connect via SATA or SAS cables within the computer case. External drives sit in enclosures outside the computer and use USB or other interfaces to connect for data transfer. There are key differences between internal and external hard drives.
Internal HDDs
- Mount directly into drive bays
- Faster speeds with SATA/SAS interfaces
- Typically higher capacities
- Not portable for use between systems
- Allow custom builds and upgrades
External HDDs
- Portable drives to move between systems
- Protective enclosure provides durability
- Typically 2.5-inch form factors
- Lower capacities than internal drives
- Use USB or other external interfaces
Both internal and external HDDs provide inexpensive bulk storage. Internal HDDs maximize performance while external HDDs provide convenient portability. For a computer’s primary storage, internal HDDs are generally preferred. External HDDs serve as easily moveable backup storage or expanded capacity.
HDD Manufacturers
There are three major companies that produce hard drives today, in order of market share:
Western Digital
Western Digital (WD) is the top selling HDD brand, with over 25% market share in 2022. They produce a full range of storage devices including hard drives, SSDs, and memory cards. WD acquired noted HDD maker Hitachi in 2012. Their hard drives span all common form factors and interfaces under brands like WD Blue and WD Black for consumers and WD Gold for enterprises.
Seagate
Another huge player in the storage market, Seagate holds around 25% of the HDD market. Seagate makes drives for desktops, laptops, NAS devices, and enterprise storage systems. Their HDD products include the Barracuda, Firecuda, Ironwolf, and Exos drive families. They produce 3.5-inch and 2.5-inch HDDs with SATA and SAS interfaces.
Toshiba
Toshiba is a leader in flash storage and also manufactures around 17% of the world’s hard drives after acquiring Fujitsu’s HDD division. Their drives serve consumer and enterprise segments with SATA, SAS, and USB interfaces. Toshiba HDD product lines include the N300, X300, P300, and MG series.
Other companies producing HDDs include Samsung and Micron, though at lower shipment numbers than the big three manufacturers.
Hybrid Hard Drives
Hybrid hard drives (HHDs), also known as hybrid drives or solid-state hybrid drives (SSHDs), combine flash memory with traditional HDDs for improved performance. A small amount of high-speed NAND flash, usually 8-16GB worth, is paired with a standard spinning hard drive through an integrated controller.
The HHD controller uses algorithms to monitor data requests and learns what data is accessed most frequently. This “hot” data gets copied over to the flash memory side for ultra-fast access times approaching SSD speeds. Everything else stays stored on the HDD side. The end result aims to approach SSD performance for the most oft-used files while providing tons of HDD capacity for bulk storage.
HHDs sell at slightly higher prices than normal HDDs but significantly less than SSDs. They can boost system performance over HDDs in many workflows while providing way more capacity than SSDs. However, they lag pure SSD speeds, and the flash portion does essentially just cache data rather than provide primary storage.
HHD use cases include budget gaming rigs needing better loading times or typical desktops where a full SSD would be prohibitively expensive compared to the minor speed gains. In most systems, either a pure HDD or SSD usually makes more sense than a hybrid drive.
Solid State Drives vs. Hard Disk Drives
The other major type of storage device today is solid state drives (SSDs). Comparing SSDs vs HDDs shows the pros and cons of each technology.
SSD Advantages
- Faster read/write speeds (up to 550/500 MB/s for SATA III SSDs)
- Silent with no moving parts
- Lower heat output and power draw
- Higher max G-force shock resistance
- Smaller size and often lighter weight
HDD Advantages
- Significantly cheaper per gigabyte
- Higher storage capacities available
- Mature, well-proven technology
- Easy to source replacements/upgrades
SSDs excel at speed while HDDs win at capacity and affordability. For systems needing top performance like gaming PCs or quick booting drives, SSDs are the clear choice. When bulk storage and low cost are priorities, HDDs carry the day.
Conclusions
Hard disk drives remain the most common internal storage component in desktop and laptop PCs today. HDD technology offers a compelling mix of performance and very high capacities at affordable prices. Their moving parts mean HDDs are limited in speed compared to SSDs, but the low cost per gigabyte makes them ideal for bulk storage needs.
3.5-inch and 2.5-inch form factors with SATA interfaces dominate the HDD market. Advancements like SMR boost densities while helium drives improve efficiency. HDDs will continue to serve critical roles in PCs and data centers into the future, coexisting and complementing SSDs as a fundamental storage technology.
